(ED-This tip comes from the folks at Yamaha Motor Corp. and while it
was written for its dealers, the information is applicable to almost all
snowmobile models. It's timely, as well, because we're all ready to get our
sleds out of storage and prep them for the coming winter season.)
Storing gasoline does not automatically change its basic
properties or performance characteristics. When done properly, gasoline can be
stored for extended periods of time.
Even the manufacturers say you can store their gasoline for
up to a year "provided you use a sealed, non-vented container and store it in a
cool, dry location that does not experience wide temperature changes."
You can see that a snowmobile's fuel tank and fuel system doesn't
meet the above requirements. Those same manufacturers say that the maximum
storage period falls to about 30 days when stored in your average snowmobile.
This is due to the fact that the snowmobile's fuel system is not sealed. Sleds
are usually stored from spring through fall in warm and humid conditions and
often under wide temperature changes. Consequently, a snowmobile experiences
some of the worst possible conditions of any type of motorsport product when
fuel is left in it for more than 30 days.
The situations below explain some of the bad affects that
can happen to gasoline that is left sitting in a snowmobile too long. The
information comes directly from gasoline manufacturers and sheds some light on
why it is so important to drain the fuel system if the unit will not be used
for a length of time.
Volatility And Light Ends
Volatility describes a gasoline's ability to form vapors.
Liquid gasoline does not burn; only gasoline vapors burn. So, gasoline
manufacturers must include a mixture of components called "light ends" that
promote vaporization of the fuel. The light ends are what allow the fuel to
ignite easily at first start-up whenever the engine is cold. As temperatures
get colder, more light ends are needed to ignite the fuel.
This is one reason why the volatility of gasoline is
tailored for the range of temperatures expected in the region where it is sold.
"Winter gasoline" has a higher volatility or more light ends for easy starting
in cold weather. Conversely, "summer gasoline" has a lower volatility because
less light ends are needed. Using less light ends also reduces the amount of
vapors that escape to the atmosphere and contribute to smog formation.
In order to start a cold engine, enough light ends must be
present in the gasoline to vaporize at the engine's temperature and form a
combustible vapor-air mixture. The colder the engine's temperature at start-up,
the more light ends are needed to ignite easily when the engine is cranked.
When temperatures drop to snowmobile season levels, light ends become critical
for cold starting.
Evaporation-Loss Of Light Ends
The gasoline light ends needed for easy starting vaporize
during storage just as they do during normal use. If the storage container is
not sealed tightly, some of the light ends will gradually be lost. Too great a
loss decreases the gasoline's ability to start an engine again, especially in
During storage, evaporation of gasoline from a vented fuel
tank can be minimized if the temperature of the vehicle is kept constant.
Temperature changes can cause the temperature of the tank to cycle. The heating
portion of the cycle raises the pressure of the gasoline vapor and air above
the liquid gasoline, which, in turn, drives some of the vapor-air mixture out
through the vent system. The succeeding cooling cycle lowers the pressure vapor
and air, drawing fresh air back into the fuel tank. Light ends evaporate from
the gasoline and saturate the new air. The repetition of the cycle gradually
pumps light ends out of the gasoline inside the tank. Since the fresh air being
drawn into the fuel tank also contains moisture, especially during periods of
high humidity, the cycling of the air also brings water vapor into the fuel
tank. If the water vapor condenses during the cooling cycle, it ends up as
water in the fuel. Since high humidity is common, during the summer storage
season, water in the gas and corrosion in the fuel system is another potential
The larger the surface area of the gasoline exposed to the
air, the more vaporization occurs and the more light ends will be lost. Higher
temperature and wider changes in temperature also increase light end loss. So,
keeping the container full and controlling the temperature fluctuations will
minimize the loss of light ends, the exposure of gasoline to the air, and the
contamination of the gasoline with water.
Oxidation-Formation Of Gum
Except for added oxygenates, gasoline is made up almost
entirely of hydrocarbons-molecules that are constructed from hydrogen and
carbon. Hydrocarbons, as a class, are chemically stable molecules. However,
there are types of hydrocarbons in gasoline (olefins and diolefins) that can
combine slowly with the oxygen in the air and cause oxidation. The products of
this reaction are larger molecules called "gum."
Warmer temperature also accelerates formations of gum. This
is another reason why it is recommended to control the temperature of stored
gasoline. Most gasoline contains negligible amounts of gum when they are
manufactured and most contain chemicals called "stabilizers" that retard gum
formation. It is the stabilizers that make it possible to store gasoline for a
considerable time period when the conditions are good.
The gum formed by oxidation is usually soluble in gasoline. However,
it remains behind as a sticky residue when the gasoline evaporates. Since
gasoline begins to evaporate in the carburetor of a carbureted engine or in the
injector of a fuel-injected engine, a gasoline containing soluble gum may leave
a deposit on these parts and on the intake valves. These gum deposits will be
in addition to the normal deposits formed by gasoline which are triggered by
higher engine temperatures.
Engines run best when vital engine parts are clean.
Carburetor and fuel injector deposits can cause hesitation and stumbling on
acceleration, lower fuel economy, lower power output and higher emissions of
hydrocarbons and carbon monoxide. Excessive intake valve deposits can cause
many of the same performance problems, plus higher emissions of hydrocarbons,
carbon monoxide, and nitrogen oxides. The EPA recognizes that fuel system
deposits increase emissions, so they require all gasoline to contain a
deposit-control additive. All deposit-control additives keep deposits from
forming; the best ones clean up deposits formed by lower-quality gasoline.
If the gasoline contains a lot of soluble gum, the normal
level of deposit-control additive may not be sufficient. This is why it is
sometimes recommended to treat a tank of gasoline with an extra dose of
deposit-control additive if a vehicle displays driveability problems after
being stored. The gum-forming reactions become faster as the temperature of the
Severe oxidation of gasoline may produce insoluble gum. The insoluble
gum will take the form of brown or black particles which float in the gasoline
or settle to the bottom of the container.
When an engine is fueled with gasoline containing insoluble
gum, the fuel filter will remove the gum. If the engine has an in-tank fuel
pump, the screen on the pump's feed also may capture some of the gum. However,
these devices can become plugged if the gasoline contains too much insoluble
gum. This will cause the engine to lose power or stall because it is starved
for fuel. Adding a deposit-control additive will not keep insoluble gum from
plugging filters and screens.
The information above makes clear the following
Avoid leaving fuel in a snowmobile for more than
30 days unless it is in a cool and dry location and won't see wide temperature
If fuel must be left in the sled, use fuel
stabilizer in the tank and be sure to run it through the system. Fill the tank
with fuel and drain the carburetors.
Warm and humid weather is the worst possible
condition for storage, Anytime the sled is parked, it should be in a cool and
dry location that won't experience wide temperature fluctuations.