What does my oil actually do?

An engine oils job is primarily to stop all the metal surfaces in your engine from grinding together. But it
also has to dissipate the heat generated from this friction too. It also transfers heat away from the
combustion cycle. Another function is that a good oil must be able to hold in suspension the nasty
by-products of fuel combustion, such as silica and acids, whilst also cleaning the engine of such nasties.
And it must do all of these things under tremendous heat and pressure.

What if I don't use the OEM recommended oil, will my warranty be voided?

When choosing a two stroke snowmobile injector oil, most owners are inclined to follow the advice of
their dealer and their owners manual. This is the best practice and will give the owner of a new sled
peace of mind.
But snowmobile owners should be aware that NONE of the snowmobile manufacturers
warranties are contingent on the use of the manufacturers brand oil.

Aftermarket oil, are they really the same as the O.E.M. oil?

OEM manufacturers oils are produced by specialty lubricant manufacturers, not the OEM, (as far as we know:
Yamaha=Torco, Skidoo=Castrol, Arctic Cat and Polaris=LubeTech), and these
formulas are tested and approved by the manufacturer for use in their sleds (standards vary).

What do the Oil Manufacturer Ratings mean?

Some different ratings you may see are: API TC, TC-W3, JASO and ISO-L-EGD.

In North America oil is usually given a rating from the American Petroleum Institute (API) of "TC", the
Boating Industry Association (BIA) rating of "TC-W", or the National Marine
Manufacturers Association (NMMA) rating of "TC-W II."

To prevent carbon buildup in the piston ring grooves, these TC oils used metal
based detergents that were very effective in motorcycle engines but caused
some problems in outboard engines operated at long periods of time at
one throttle setting.

When the BIA developed the TC-W rating, they excluded the use
of these metal-based detergents in favor of organic detergents to eliminate this
problem in outboard engines.
These TC-W oils (two-cycle, water cooled) also contained
lighter base oils. For engines operating in the 4,000 rpm to 5,000 rpm range,
it had no affect on piston and bearing life.
However, off-road motorcyclists testing these new TC-W oils were disappointed with
the bearing life of their engines operating at 10,000 - 11,000 rpm and quickly returned to
using the TC oils.

The BIA evolved into the National Marine Manufacturers Association (NMMA).
The need for a clean two-stroke outboard oil was recognized when piston ring groove
carbonization was seen
as a primary cause for engine failure and a new formula designated
TC-W II was developed.
While this oil was significantly better for outboard use and was phosphate free, it still was
not the optimum two-stroke oil for engines operating above 8,000 rpm

In Europe and the Far East, 2 stroke engine manufacturers have determined that
they need still higher quality levels for two-stroke lubricants.

In Japan, manufacturers have developed a series of strenuous engine tests. They tested
over 250 samples of two-stroke oils worldwide and used the survey results to
establish these engine tests. This became the JASO classification system.

The tests include a detergency test, lubricity test, initial torque test, exhaust smoke test
and exhaust blocking test.
These tests have a much closer connection to actual snowmobile engine applications
compared to TC-W3 tests which are all conducted on raw-water cooled outboard engines.
And for the first time ever, an oil can fail the test if it smokes too much!

The detergency test evaluates the oil's ability to maintain the cleanliness of critical engine
parts, including exhaust power valves. This is very important on power valve equipped
Rotax,Yamaha and Polaris engines.

The lubricity test measures two things:

* First, the engine is run with a load for 50 minutes then the cooling system is disconnected
for ten minutes and the resulting drop in horsepower is recorded. This cycle is repeated
several times and each drop in power is compared and it must not vary more than a specified
amount or be more than a specified amount.
* Then the engine is run with increasingly leaner oil ratios: 60:1, 100:1 then 150:1. If no
seizure occurs and power is maintained within a specified percentage, the oil passes.
The initial torque test measures the engine's startability when cold, an important
consideration for 3-cylinder 800cc sleds.

The exhaust blocking and smoking tests are run by mixing the test oil at an over-rich
10:1 ratio and running it in a two-stroke portable generator. The exhaust blocking test
simply examines the pencil sized exhaust outlet for carbon blocking.
At a 10:1 ratio, these tests are very hard to pass.
The highest JASO rating is FD. Lower ratings are "FC", "FB" and "FA."

In Europe, two-cycle engine manufacturers were simultaneously working on
two-cycle oil tests to separate the cheap, poor quality oils from the top quality oils.
They tested the JASO reference oils in European engines and their top reference oils in
Japanese engines.
They found that European two-stroke high performance engines
needed an oil with a better detergency and higher temperature performance than
the best JASO "FD" oils.

In April, 1997, they published their ISO global standards for two-stroke oils with two
quality level categories: ISO-L-EGB and ISO-L-EGC.
The ISO-L-EGB aligns closely with JASO "FB" and the
ISO-L-EGC aligns closely with JASO "FD" for minimum test standards.

Running these tests is a very expensive and time consuming effort but in the end, a
bottle of oil with one of these JASO FD/ISO- L-EGD certified ratings means that the oil
meets the highest quality tests set by the engine manufacturer in Japan and Europe.

Polaris has recognized the "all-in-one" advantages of TC-W3 two-stroke oil and recommends
the use of TC-W3 oils in their watercraft and snowmobiles.
Interestingly, their new synthetic "gold" oil is not TC-W3 approved, it is the new JASO FD/ISO-L-EGD approved oil!

Ski-Doo, however, specifically prohibits the use of TC-W3 oils in their snowmobiles
and Sea-Doo watercraft, they recommended ISO-L-EGD oils while Yamaha recommends
JASO "FD." All of this may seem confusing and will probably make the choice of
snowmobile lubricants even more difficult.

In short, TC-W3 oils have a 10% higher level of lubricity than TC-W II oils and are
a better choice for snowmobiles than any previous outboard oils.

However, specially formulated snowmobile oils that pass JASO FD/ISO-L-EGD
and do not follow NMMA restrictions will provide much better protection for higher
rpm applications (snowmobiles/motorcycles) and still provide a superior lubricity
and detergency than TC-W3 oils at the same cost with less smoke.
So, use snowmobile oil in your snowmobile and outboard oil in your outboard engine.

What are the Base Oil types?

Base oils compose from 50% to 95% of the total weight of the 2-stroke engine oil.  They fall into 2
general categories: synthetic and petroleum based.

  • Petrolium/mineral oils are based on oil that comes from Mother Earth which has been refined.
  • Pure Synthetic oils are entirely concocted by chemists in oil company laboratories.

    The only other type is semi-synthetic, sometimes called premium, which is a blend of the two.

What are Pure Synthetic oils?

Pure synthetic oils are the types concocted by chemists. They break apart the molecules that make up a
variety of substances and then recombine the individual atoms that make up those molecules to build
new, synthetic molecules. This process allows the chemists to actually "fine tune" the molecules as they
build them.

  • Synthetics will not decompose as easily at high engine temperatures as petroleum. This added
    stability at high temperature means that the engine wont burn as much oil and that means less
    sludge and fewer varnish deposits in the engine.
  • Added lubricity is another attribute of synthetics. Regular petrolium/mineral-based oil will not
    remain as a boundary layer on metal surfaces when an engine is turned off.
    Petrolium/mineral-based oil drains off parts and out of passageways.
    Additionally, mineral-based oils contain waxes and paraffins that come out of the earth and
    solidify when it gets colder outside, therefore making it even harder to pump the oil when cold.
  • Higher film strength is one of the major benefits of synthetics. Film strength is what keeps oil
    molecules from being pushed away from each other under pressure. Mineral based oil has a film
    strength of about 400 psi, while synthetics usually exceed 3000 psi. In an area where two metal
    surfaces meet, the film of oil between them prevents them from rubbing and wearing away at each
  • Synthetic base oils reduce carbon buildup, smoke output and help lower the pour point
    (pour temperature).

Are all synthetics the same?

NO. There are wide differences in quality and protection provided by the various synthetics.
Additionally, not all synthetics are 100% synthetic. Many are partial synthetics marketed under the
perception of full synthetics to the unsuspecting consumer. There has been a lot of litigation flying
around about what really constitutes a ‘true synthetic’ oil in the last several years. There is no
universally accepted definition for synthetic oil. Each manufacturer is free to label their product
‘synthetic’ by whatever rules the manufacturer chooses.
Read the labels and compare ratings.

Is the extra cost over the petroleum based oils worth it in the long run?

Synthetic base oils used in two-stroke formulas reduce carbon buildup, smoke output and help lower
the pour point (that's the temperature at which a fluid changes from a solid state to a flow able liquid)
of the finished formula. Less carbon buildup on the piston top and sparkplug translates to less chance
for stuck power valves and detonation, and detonation is known to be the #1 killer of snowmobile engines!
The #2 killer of snowmobile engines is overly lean carburetion and the #1 cause of overly
lean carburetion is usually clogged or iced pilot or main jets.
When snowmobiles are stored during the summer, it is very common for the fuel remaining in the
float bowls to oxidize and form corrosion or varnish on the main and pilot jets.
If these jets are not cleaned or replaced in the fall, the engine will run lean off idle and at full throttle
leading to an eventual burn down. I've noticed that these jets rarely have these
problems in motocross bikes where oil is premixed with the gas since the
oil and the anti-corrosion additives in the oil prevent these problems.
Before storing my sled I always make a batch of gas/oil mix and run it in the sled to make
sure that the carburetor internals are protected from corrosion.
A mix ratio of 50:1 to 100:1 is all it takes.

If your sled smokes excessively while trail riding (you know who you are!) you might consider trying
one of the synthetic snowmobile oils available instead of the petroleum OEM oils. These oils are
going to cost more money but the benefits will be reduced carbon deposits and much less smoke.
Your friends will be thanking you!

Synthetic and synthetic blend oils offer advantages over conventional mineral oil products.
They are better in extremes of heat and cold. They provide better oxidation resistance and
thermal stability. Their extra cost is offset by the benefits a properly formulated product
provides to your motorcycle engine. Compared to mineral-based engine oils, as we've
stated, the oxidation resistance is far superior, the friction in both the application and the
fluid, itself, is less and the synthetic products have much better low-temperature properties.
The film strength of synthetic products is also better as is the natural detergency of synthetic
base fluids, in particular, the diesters. They cost more but in most cases can be cost effective
if increases in fuel economy, engine longevity, extended drain intervals and decreased operating
temperatures, particularly, are taken into account.

Benefits of synthetic blends and synthetic oils can be summarized as follows:
* Extended drain intervals possible due to greater resistance to oxidation
* Increase in fuel economy due to the lower internal friction due to even molecular structure.
* Reduced wear in the engine due to greater film strength of the synthetic compared with mineral oils.
* Cooler running engine since less friction causes less heat. This relates to oil temperature and not
water temperature, which is controlled.
* Better cold flow characteristics due to less internal friction and very low pour points
* Faster oil flow on start up due to low pour points/less internal friction
* Cleaner engine since PAO and diesters have a high natural detergency plus
detergent/dispersant additive use.
The oils are blended according to a formula that has been developed for two-stroke engines.

What is Carbon Residue and ASH?

Ash is the non-combustible residue of a lubrication oil or fuel. Detergent additives contain metallic
derivatives, such as calcium, barium and magnesium sulfonates that are common sources of ash. Ash
deposits can impair engine efficiency and power. 

But, detergents are an important component of engine oil that help control varnish deposits, piston ring
deposits and rust (yes, rust) by keeping insoluble combustion particles from adhering to metal surfaces.
In some cases, detergents neutralize acids formed from combustion of the fuel mixture. Ash deposits
may have a grayish color, whereas carbon residue is usually black and sooty.

Carbon residue, on the other hand, is different from ash. Carbon residue is formed from unburned and
partially burned fuel, and from burning of the crankcase lubricant. Water from condensation of
combustion products along with carbon residue from fuel contribute to engine piston deposits. Carbon
de posits are normally black and have a sooty appearance.

What are oil additives?

Additives are combined with the base oil to fix certain faults with the base oil or stretch the limits of the
base oil in some cases. Additives are complex chemicals that account for most of the cost of a bottle of
2-stroke oil.

Additives for 2-stroke oils fall into several general categories:
1) Detergents,
2) Antiwear agents,
3) Biodegradability components,
4) antioxidants.

Since the lubricating oil must burn as part of the
combustion process in a 2-stroke engine, the residue resulting from this combustion process must be
swept away after each firing stroke. Detergents must be added to the oil to prevent build up and plug the
exhaust port and stick the rings and power valve(s). The two types of detergents most commonly used
in 2-stoke oil formations are Ashless and Low Ash.

  • Ashless detergents work well in engines where an excess of cooling capacity is available and
    power valves are not used.  
  • Low Ash detergent are used in most API-TC, JASO and ISO certified 2-stroke oils. These oils are
    designed for high performance engines that operate under severe load/temperature conditions.

It is important to note that oil designed to meet TC-W3 specs only (Ashless) will not protect an
engine requiring API-TC (Low Ash) type oil.

When 2-stroke oil is kept within its temperature limits, it provides an adequate protective film between
all moving parts. When that maximum temperature is exceeded, the oil film breaks down and usually
seizure occurs unless another line of defense is added to the oil mixture. These are the Antiwear
agents. These Zinc compounds flow in with the oil and are never used unless the base oil breaks down.
If the base oil breaks down, they form a protective barrier between the moving parts.

Switching Oils(?)

When switching to a synthetic oil, it is important to keep several things in mind.
Although many synthetic oil manufacturers tout the compatibility of their oils with
petrolium/mineral-based oils, adding petrolium/mineral oil to synthetic oil will drastically
reduce the level of engine protection that was initially designed into the synthetic oil.
Also, as the petrolium/mineral oil breaks down it will contaminate the
rest of the oil, leaving sludge and varnish deposits in the engine.

  • If you've been driving around with petrolium/mineral oil in your engine for years, it may not be a
    good idea to switch to synthetic oil without preparation. Synthetic oils have been known to dislodge
    the baked-on deposits from petrolium/mineral oils and leave them floating around your engine.
    It's wise to use a flushing oil first.
  • If you do decide to change, only go up the scale. If you've been running around on synthetic, don't
    change down to a petrolium/mineral-based oil, your engine might not be able to cope with the
    degradation in lubrication. Consequently, if you've been using petrolium/mineral oil, try a semi
    or a full synthetic oil. Be aware that thicker petrolium/mineral oils mean thicker layers of oil
    coating the moving parts, switching to a thinner synthetic oil can cause piston rings to leak and in
    some very rare cases, piston slap or crank vibration.
  • With the makeup of synthetic oils being different from petrolium/mineral oils,
    petrolium/mineral oil soaked gaskets and seals have been known to
    leak when exposed to synthetic oils. Perhaps not that common an occurrence,
    but worth bearing in mind nevertheless.
  • Special precautions should be taken when changing from a product
    designed primarily for water-cooled engines to an air-cooled product,
    particularly in oil injection systems where the undiluted oils would be
    mixed together. It is recommended that the oil reservoir and lines be
    drained when changing to another formulation. In applications where the
    oil is premixed with the fuel, it is recommended the fuel tank(s) be drained.

What should I do to prevent oil-related problems?

  • It is recommended that you follow the proper procedures when switching oils,
    see Switching Oils above.
  • It may sound very simple but whenever filling or topping up your oil reservoir,
    be extremely careful not to let snow or rain enter the tank. The slightest
    amount of moisture in the oil reservoir could eventually lead to a blockage in the oil
    pickup or feed line.
  • Also, remember to tighten the fill cap! I’ve seen this happen before where the cap
    comes lose and is lost somewhere in the belly pan of the snowmobile and a
    major mess is sure to follow. Oil on the disc brake rotor is no joke!
  • Remember, adjusting throttle cables at the carburetor significantly changes the
    oil mixing ratio!
  • Get accustomed to your sleds thirst for oil and if you notice a sudden reduction
    in consumption (less than 500ml after a 40 litre fill-up), take immediate action!
  • A worthwhile precaution in the above mentioned scenario is to empty 500ml of
    two-stroke oil into a friends machine, add 300ml of gasoline to the remaining
    500ml of oil, shake and pour directly into your fuel tank. This will get you home
    on roughly an 80:1 mix. If your autolube system failed or became blocked with ice,
    this should save some major expenses and headaches!

Engine Oil Shelf Life Information

In general, liquid lubricants (ie. oils, not greases) will remain intact for a number of years.
The main factor affecting the life of the oil is the storage condition for the products.
Exposure to extreme temperature changes,
and moisture will reduce the shelf life of the lubricants. Best to keep them sealed and unopened.

As a general rule, the simpler the oil formulation, the longer the shelf life. The following is a guideline under
protected conditions:

  • Base Oils, Process Oils - 3 years
  • Hydraulic Oils, Compressor Oils, General Purpose Lubricating Oils - 2 years
  • Engine Oils and Transmission Oils - 3 years
  • Industrial and Automotive Gear Oils - 2 years
  • Metal Working and Cutting Oils - 1 year

The following are signs of storage instability in a lubricant:

  • Settling out of the additives as a gel or sticky liquid
  • Floc or haze
  • Precipitates/solid material
  • Color change or haziness

Water contamination in a lubricant can be detected by a "milky" appearance of the product.

All of the above information obtained from various web sites, if you are unsure or require more
information your OEM is always a reliable source of info.

Oil Information
Spark Plug Information
Top of Page

Regardless of what type of fuel you use, it only has a shelf life of about 2 months!

The fuel left in your tank at the end of last season is NO GOOD this season!
It is not worth your while to burn it. Drain it out of your carbs (if you have them),
and start with a topped up tank of new fuel.



Use a regular unleaded gasoline with a minimum octane rating of 87. In many areas, oxygenates
(either ethanol or MTBE) are added to the gasoline. Oxygenated gasolines, containing up to 10%
ethanol or up to 15% MTBE, are acceptable gasolines. Arctic Cat suggests that whenever using
oxygenated gasolines, the carburetor main jet must be one size larger than the main jet required
for regular unleaded gasoline. When using ethanol blended gasoline, it is not necessary to add a
gasoline antifreeze since ethanol will prevent the accumulation of moisture.


Do not use white gas or gasolines containing methanol. Only Arctic Cat approved gasoline additives
should be used.



Use regular unleaded gasoline, available from most service stations, or oxygenated fuel containing
less than 10% of ethanol or methanol. The gasoline used must have an octane number of 87 or higher.
There’s a great deal of variability in the quality of the 87 octane gasoline available across the country.
So we encourage the use of premium fuel when possible.

CAUTION: Never experiment with other fuels or fuel ratios. Never use fuel containing more than
10% alcohol, (ethanol or methanol). The use of non-recommended fuel can result in snowmobile
performance deterioration and damage to critical parts in the fuel system and engine components.



Most Polaris engines are designed to run on 87 octane non-oxygenated or 89 oxygenated pump gasoline.
There’s a great deal of variability in the quality of the 87 octane gasoline available across the country.
So we encourage the use of premium fuel when possible.

NOTE: Some Polaris snowmobiles require premium gasoline. Check your Owners Manual Supplement
to determine what type of fuel your machine needs.

Premium Fuel Switch

Some Polaris snowmobiles are equipped with a key function to adjust the timing on the machine as
you change fuels. It’s very important to the life of your engine that you use this feature. When using
fuels with a pump-posted octane rating of 91 or higher, turn the key switch to “ON/PREM.” When the
engine is started, a yellow “Premium Fuel” light
illuminates on the instrument panel. When the key is in this position, the fuel must be a minimum
of 91 octane. Most high performance machines require the use of premium fuels. Substituting other
fuels may cause engine damage.


Using lower than recommended octane fuels or operating with obstructed fuel systems will lead to
costly engine damage. If you are uncertain about the quality or octane rating of the fuel you use,
turn your key switch to “ ON/REG.” The Premium Fuel light will go out. This setting will adjust the
timing of your engine to run on fuels with 87 octane or higher.

Fuel System De-icers

If you use non-oxygenated fuel, Polaris recommends the regular use of isopropylbased fuel
system de-icer. Never use de-icers or additives containing methanol. If you use oxygenated
fuel containing ethanol, additional alcohol deicers or water absorbing additives are not required
and should not be used.



Unleaded gasoline Pump octane 88 or higher


Oxygenated fuels (gasohol) containing a maximum 5% of ethanol can be used, although
richer jetting may be required to prevent engine damage. For details consult a Yamaha dealer.
Gasohol containing methanol is not recommended. Make sure that snow or ice does not enter
the fuel tank when refueling. Do not use alcohol deicers or water absorbing additives with
oxygenated fuel. The fuel tank should be filled with straight gasoline as specified.

Spark Plug
Oil Information
Fuel Information
Top of Page
Spark Plug FAQs

Q: How often should I replace my spark plugs?

A: Unfortunately, there is no single answer to this question. As spark plugs grow older, they lose their sharp edges as material from the center and ground electrodes is slowly eroded away. As the gap between these two points grows, the voltage required to bridge the gap increases proportionately. Even the best ignition systems will be strained to supply enough voltage to completely burn the fuel. It is at this point, when fuel is being left unburned, that the time has come to change spark plugs.

Replacing worn out spark plugs with new ones (with sharp new edges) effectively restores the ignition systems efficiency. Misfires are reduced, power is restored, economy of operation is enhanced and emissions are reduced.

The best guide is the manufacturers recommendation for your vehicle, as this particular service varies from brand to brand and model to model. In the absence of this information or in conjunction with it, you can rely on the advice of a mechanic who is familiar with your type of vehicle.

Q: How do I choose the right spark plug?

A: There are several factors such as thread reach, thread diameter, the insulator nose projection and whether the spark plug incorporates a gasket or is of the conical type, to consider when choosing the correct spark plug for your needs.

In most cases, it is not until the engine is modified, or the compression is raised significantly, that stock ignition systems and spark plugs begin to show signs of being inadequate. At this point, a variety of factors determine which spark plug will be best suited for a particular configuration. In these modified engines, specific electrode/tip combinations, electrode materials and colder heat ranges can provide measurable gains in power. If your vehicle has had extensive modifications, it would be best to seek the advice of the manufacturer of your vehicle, the aftermarket supplier who manufactured your modifications, or your mechanic.

Q: How do I "read" a spark plug?

A: Being able to "read" a spark plug can be a valuable tuning aid. By examining the insulator firing nose color, an experienced engine tuner can determine a great deal about the engines overall operating condition.

In general, a light tan/gray color tells you that the spark plug is operating at optimum temperature and that the engine is in good condition. Dark coloring, such as heavy black wet or dry deposits can indicate an overly-rich condition, too cold a heat range spark plug, a possible vacuum leak, low compression, overly retarded timing or too large a plug gap. If the deposits are wet, it can be an indication of a breached head gasket, poor oil control from ring or valvetrain problems or an extremely rich condition - depending on the nature of the liquid present at the firing tip.

Signs of fouling or excessive heat must be traced quickly to prevent further deterioration of performance and possible engine damage.

Q: How much of a performance improvement can I expect from changing plugs?

A: A common misconception is that changing spark plugs will result in a large power increase. In most cases, removing even seriously worn out spark plugs will only result in very modest power gains, typically about 1-2% of total engine output. This could be even less for computer-controlled vehicles, primarily because most newer vehicles have more powerful ignition systems and the vehicles computer can make adjustments so that vehicle operation seems smoother and more seamless.

Many people think that simply supplying more spark to the firing tip can and will combust more fuel. What they don't understand is that most newer engines are so efficient that they are already burning all of the available fuel. Simply adding more spark voltage can't burn more fuel because there is no more fuel to burn.

When a stock or near-stock engine is given a fresh set of spark plugs, peak efficiency is restored. The power gains that come from this restored state of tune are usually minimal. Any company that tells you that their spark plug will provide significant gains in power in a stock or near-stock engine is making blanket statements that may not be supportable.

Q: What is a "fouled" spark plug?

A: A spark plug is considered fouled when the insulator nose at the firing tip becomes coated with a foreign substance such as fuel, oil or carbon. This coating makes it easier for the voltage to follow along the insulator nose, leach back down into the metal shell and ground out rather than bridging the gap and firing normally.

Many factors can contribute to spark plug fouling. The air/fuel ratio may be too rich as a result of incorrect carburetor adjustment or a poorly performing fuel injection system. Worn piston rings may allow too much oil to leak into the combustion chamber, leading to oil fouling. The ignition system may not be performing properly. Prolonged idling or continuous low-speed driving may keep the spark plug from reaching its optimum operating temperature. Using too cold a spark plug can lead to the same problem. Finally, a dirty air filter can create a too-rich condition which can lead to fouling.

Fuel, oil and carbon fouling can all be the result of different causes but, once a spark plug is fouled, it will not provide adequate voltage to the firing tip and that cylinder will not fire properly. In many cases, the spark plug cannot be cleaned sufficiently to restore normal operation. Therefore, it is recommended that a plug be replaced once it is fouled.

Q: How do I install spark plugs correctly?

A: It is essential to tighten a spark plug to the specified turning angle or torque setting. First, screw in the plug finger tight until the gasket meets the cylinder head. Then seat the plug/gasket with a torque or turning angle wrench as specified in your manual.

This is very important, as excessive tightening of a spark plug can cause breakage of the metal shell and damage to the interior seals. At the same time, insufficient tightening can lead to overheating of the spark plug and potential detonation.

Q: Why are there different heat ranges?

A: It is a common misconception that spark plugs create heat. They don't. A heat range refers to how much heat a spark plug is capable of removing from the combustion chamber.

Selecting a spark plug with the proper heat range will insure that the tip will maintain a temperature high enough to prevent fouling yet be cool enough to prevent pre-ignition. While there are many things that can cause pre-ignition, selecting a spark plug in the proper heat range will ensure that the spark plug itself is not a hot spot source.

Q: What do the numbers and letters in a part number represent?

Each manufacturers have their own numbering system.
Here is an example of NGKs Spark Plug Number Breakdown:

plug info

Q: Does compression ratio affect firing end temperature?

A: Yes, the by-product of increased compression is the elevation in cylinder temperatures. This is why it is recommended to choose a spark plug suitable for your application. NGK Spark Plugs recommends dropping heat ranges and altering Air/Fuel mixtures and timing as needed. It is very important to dissipate the excess heat from the combustion chamber in order to prevent pre-ignition.

Q: Can old spark plugs be cleaned?

A: Yes, you can clean spark plugs. However, it is good to remember that spark plugs are a wearable item, so it's important to make sure you check to see if it's worth cleaning before you go through the following steps.
• If the firing end is wet, make sure you clean the spark plug with
a quick drying cleaner. (Examples: contact cleaner or brake cleaner).

• Sand blast the spark plug using low air pressure
and use a dry compound.

• Completely blow all the sand from the spark plug.

• Using a wire brush clean the threads and re-gap.

NOTE: Insufficient cleaning of the spark plug may lead to spark plug failure in a very short period of time. Clean the spark plug thoroughly to avoid problems later. Remember, if a spark plug is fouling it's usually a result of engine side factors or incorrect heat range selection.

Q: What is pre-ignition?

A: Pre-ignition is defined as the ignition of the air/fuel mixture before desired ignition timing.

Q: What is detonation?

A: Detonation is a spark plugs worst enemy. It can break insulators and ground electrodes. Spark plug temperatures can reach in excess of 3000 °F.

Detonation, in simple terms, is a violent uncontrolled burn of the air/fuel mixture, which occurs when excessive heat and cylinder pressure causes the air/fuel mixture to spontaneously ignite.


Installing spark plugs:

Torque is one of the most critical aspects of spark plug installation. Torque directly affects the spark plugs' ability to transfer heat out of the combustion chamber. A spark plug that is under-torqued will not be fully seated on the cylinder head, hence heat transfer will be slowed. This will tend to elevate combustion chamber temperatures to unsafe levels, and pre-ignition and detonation will usually follow. Serious engine damage is not far behind.

An over-torqued spark plug can suffer from severe stress to the Metal Shell which in turn can distort the spark plugs inner gas seals or even cause a hairline fracture to the spark plugs either case, heat transfer can again be slowed and the above mentioned conditions can occur.

The spark plug holes must always be cleaned prior to installation, otherwise you may be torquing against dirt or debris and the spark plug may actually end up under-torqued, even though your torque wrench says otherwise. Of course, you should only install spark plugs in a cool engine, because metal expands when its hot and installation may prove difficult.

Please refer to the owners manual to find your specific plug type & size and torque figures.


Since the gap size has a direct affect on the spark plugs tip temperature and on the voltage necessary to ionize (light) the air/fuel mixture, careful attention is required. While it is a popular misconception that plugs are pre-gapped from the factory, the fact remains that the gap must be adjusted for the snowmobile that the spark plug is intended for. Those with modified engines must remember that a modified engine with higher compression will typically require a smaller gap settings (to ensure ignitability in these denser air/fuel mixtures). As a rule, the more power you are making, the smaller the gap you will need.

A spark plugs voltage requirement is directly proportionate to the gap size. The larger the gap, the more voltage is needed to bridge the gap. Most experienced tuners know that opening gaps up to present a larger spark to the air/fuel mixture maximizes burn efficiency. It is for this reason that most racers add high power ignition systems. The added power allows them to open the gap yet still provide a strong spark.

With this mind, many think the larger the gap the better. In fact, some aftermarket ignition systems boast that their systems can tolerate gaps that are extreme. Be wary of such claims. In most cases, the largest gap you can run may still be smaller than you think.

Heat Range selection:

Let's make this really simple: when you need your engine to run a little cooler, run a colder plug. When you need your engine to run a little hotter, run a hotter spark plug. However, people that going to a hotter spark plug can sometimes mask a serious symptom of another problem that can lead to engine damage. Be very careful with heat ranges. Seek professional guidance if you are unsure.

With modified engines (those engines that have increased their compression) more heat is a by-product of the added power that normally comes with increased compression. In short, select one heat range colder for every 75-100 hp you add, or when you significantly raise compression. Also remember to retard the timing a little and to increase fuel enrichment and octane. These tips are critical when adding some major performance mods (turbos or nitrous kits), and failure to address ALL of these areas will virtually guarantee engine damage.

Spark plugs are one of the most misunderstood components of an engine. Numerous questions have surfaced over the years, leaving many people confused.

This guide was designed to assist the technician, hobbyist, or race mechanic in understanding, using, and troubleshooting spark plugs.

The information contained in this guide applies to all types of internal combustion engines: two stroke engines, rotary engines, high performance/racing engines and street vehicles.

Spark plugs are the "window" into your engine (your only eyewitness to the combustion chamber), and can be used as a valuable diagnostic tool. Like a patients thermometer, the spark plug displays symptoms and conditions of the engines performance.

The experienced tuner can analyze these symptoms to track down the root cause of many problems, or to determine air/fuel ratios.


The spark plug has two primary functions:

1. To ignite the air/fuel mixture
2. To remove heat from the combustion chamber

Spark plugs transmit electrical energy that turns fuel into working energy. A sufficient amount of voltage must be supplied by the ignition system to cause it to spark across the spark plugs gap. This is called "Electrical Performance."

The temperature of the spark plugs firing end must be kept low enough to prevent pre-ignition, but high enough to prevent fouling. This is called "Thermal Performance", and is determined by the heat range selected.

It is important to remember that spark plugs do not create heat, they can only remove heat. The spark plug works as a heat exchanger by pulling unwanted thermal energy away from the combustion chamber, and transferring the heat to the engines cooling system. The heat range is defined as a plugs ability to dissipate heat.

The rate of heat transfer is determined by:

1. The insulator nose length
2. Gas volume around the insulator nose
3. The materials/construction of the center electrode and porcelain insulator

A spark plugs heat range has no relationship to the actual voltage transferred though the spark plug. Rather, the heat range is a measure of the spark plugs ability to remove heat from the combustion chamber. The heat range measurement is determined by several factors; the length of the ceramic center insulator nose and its' ability to absorb and transfer combustion heat, the material composition of the insulator and center electrode material.
The insulator nose length is the distance from the firing tip of the insulator to the point where insulator meets the metal shell. Since the insulator tip is the hottest part of the spark plug, the tip temperature is a primary factor in pre-ignition and fouling. Whether the spark plugs are fitted in a lawn mower, boat, or a race car, the spark plug tip temperature must remain between 500C-850°C. If the tip temperature is lower than 500°C, the insulator area surrounding the center electrode will not be hot enough to burn off carbon and combustion chamber deposits. These accumulated deposits can result in spark plug fouling leading to misfire. If the tip temperature is higher than 850°C the spark plug will overheat which may cause the ceramic around the center electrode to blister and the electrodes to melt. This may lead to pre-ignition/detonation and expensive engine damage. In identical spark plug types, the difference from one heat range to the next is the ability to remove approximately 70°C to 100°C from the combustion chamber. A projected style spark plug firing tip temperature is increased by 10°C to 20°C.

Tip Temperature and Firing End Appearance

The firing end appearance also depends on the spark plug tip temperature. There are three basic diagnostic criteria for spark plugs: good, fouled and overheated. The borderline between the fouling and optimum operating regions is called the spark plug self-cleaning temperature. The temperature at this point is where the accumulated carbon and combustion deposits are burned off.

Bearing in mind that the insulator nose length is a determining factor in the heat range of a spark plug, the longer the insulator nose, the less heat is absorbed, and the further the heat must travel into the cylinder head water journals. This means the plug has a higher internal temperature, and is said to be a hot plug. A hot spark plug maintains a higher internal operating temperature to burn off oil and carbon deposits, and has no relationship to spark quality or intensity.

Conversely, a cold spark plug has a shorter insulator nose and absorbs more combustion chamber heat. This heat travels a shorter distance, and allows the plug to operate at a lower internal temperature. A colder heat range is necessary when the engine is modified for performance, subjected to heavy loads, or is run at high rpms for a significant period of time. The colder type removes heat more quickly, and will reduce the chance of pre-ignition/detonation and melting or damage to the firing end. (Engine temperature can affect the spark plugs operating temperature, but not the spark plugs heat range).

Below is a list of some of the possible external influences on a spark plugs operating temperatures. The following symptoms or conditions may have an effect on the actual temperature of the spark plug. The spark plug cannot create these conditions, but it must be able to cope with the levels of heat...if not, the performance will suffer and engine damage can occur.

Air/Fuel Mixtures seriously affect engine performance and spark plug operating temperatures:

1. Lean air/fuel mixtures cause plug tip and cylinder temperature to increase, resulting in pre-ignition, detonation, and possibly serious spark plug and engine damage.

2. Rich air/fuel mixtures cause tip temperature to drop, causing fouling and poor driveability.

Higher Compression Ratios will elevate spark plug tip and in-cylinder temperatures. Compression can be increased by performing any one of the following modifications:

1. Reducing combustion chamber volume (i.e.: domed pistons, smaller chamber heads, milling heads, etc.)

2. Adding forced induction (Nitrous, Turbocharging or Supercharging).

It is important to read spark plugs many times during the tuning process to achieve the optimum air/fuel mixture. As compression increases, a colder heat range plug, higher fuel octane, and careful attention to ignition timing and air/fuel ratios are necessary. Failure to select a colder spark plug can lead to spark plug/engine damage.

Advancing Ignition Timing

Advancing ignition timing can cause tip temperature to increase dramatically.

Engine Speed and Load

Increases in firing-end temperature are proportional to engine speed and load. When traveling at a consistent high rate of speed, or carrying/pushing very heavy loads, a colder heat range spark plug should be installed.

Ambient Air Temperature

As air temperature falls, air density/air volume becomes greater, resulting in leaner air/fuel mixtures. This creates higher cylinder pressures or temperatures and causes an increase in the spark plugs tip temperature. So, fuel delivery should be increased. As temperature increases, air density decreases, as does intake volume, and fuel delivery should be decreased.


As humidity increases, air intake volume decreases. This results in lower combustion pressures and temperatures, causing a decrease in the spark plugs temperature and a reduction in available power. Air/fuel mixture should be leaner, depending upon ambient temperature.

Barometric Pressure/Altitude

Also affects the spark plugs tip temperature. The higher the altitude, the lower cylinder pressure becomes. As the cylinder temperature decreases, so does the plug tip temperature. Many mechanics attempt to "chase" tuning by changing spark plug heat ranges. The real answer is to adjust jetting or air/fuel mixtures in an effort to put more air back into the engine.

Types of Abnormal Combustion


Defined as: ignition of the air/fuel mixture before the pre-set ignition timing mark. Caused by hot spots in the combustion chamber...can be caused (or amplified) by over advanced timing, too hot a spark plug, low octane fuel, lean air/fuel mixture, too high compression, or insufficient engine cooling. A change to a higher octane fuel, a colder plug, richer fuel mixture, or lower compression may be in order. You may also need to retard ignition timing, and check vehicles cooling system

Pre-ignition usually leads to detonation; pre-ignition an detonation are two separate events.


The spark plugs worst enemy! (Besides fouling). Detonation can cause insulators or ground electrodes to break off. Pre-ignition most often leads to detonation. Plug tip temperatures can spike to over 3000°F during the combustion process. Detonation is most frequently caused by hot spots in the combustion chamber. Hot spots will allow the air/fuel mixture to pre-ignite. As the piston is being forced upward by mechanical action of the connecting rod, the pre-ignited explosion will try to force the piston downward. If the piston can't go up (because of the force of the premature explosion) and it can't go down (because of the upward motion of the connecting rod), the piston will rattle from side to side. The resulting shock wave causes an audible pinging sound. This is detonation.

Most of the damage than an engine sustains when "detonating" is from excessive heat. The spark plug is damaged by both the elevated temperatures and the accompanying shock wave, or concussion.


A spark plug is said to have misfired when enough voltage has not been delivered to light off all fuel present in the combustion chamber at the proper moment of the power stroke (a few degrees before top dead center). A spark plug can deliver a weak spark (or no spark at all) for a variety of reasons...defective coil, too much compression with incorrect plug gap, dry fouled or wet fouled spark plugs, insufficient ignition timing, etc.

Slight misfires can cause a loss of performance for obvious reasons (if fuel is not lit, no energy is be-ing created). Severe misfires will cause poor fuel economy, poor driveability, and can lead to engine damage.


Fouling will occur when spark plug tip temperature is insufficient to burn off carbon, fuel, oil or other deposits. This will cause the spark to leach to the metal spark across plug gap will cause a misfire.

Wet-fouled spark plugs must be changed...spark plugs will not fire.
Dry-fouled spark plugs can sometimes be cleaned by bringing engine up to operating temperature.

Before changing fouled spark plugs, be sure to eliminate root cause of fouling.

NGK Spark Plug Guide for snowmobiles.

Spark Plug information courtesy of Snowmobile World