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Whatever gas still in the tank isn't gasoline anymore after 3 years.
Drain
it and replace the fuel filter.
I forgot about the fuel. Generally, gasoline should be consumed
within a month of purchase. Gasoline is formulated for a
cradle-to-grave consumption period of 6 weeks. If a vehicle is to be
stored for longer periods, have the gas cap checked (and check the
rubber seal), drain the gas tank, and run the car until it stops.
Gasoline in sealed containers remains at good quality for 6 months,
and that would include the closed fuel system in a car but good
quality in a car is not the same as pump quality. Again, it all
depends on HOW the vehicle was stored, like outside or in a garage.
If the gas in the tank is not used soon, if the vehicle is exposed to
direct sunlight, or the vehicle is stored at temperatures above 80° F
then a fuel stabilizer should be added to the gasoline prior to
storage. Fuel stabilizers contain antioxidants that prevent gum and
other compounds from forming in gasoline, biocides that prevent
microbial growth, and corrosion inhibitors that prevent the formation
of rust and corrosion. We use a fuel stabilizer for lawn or snow
equipment that gets stored during the off-season with their tanks
topped off at 95% (5% for liquid expansion) and add stabilizer;
however, I'm talking about storing gas for maybe 6 to 12 months, not
36 months. Stabilizer should allow the fuel to be usable (but not as
energetic) for a year. While not noticeable in a lawnmower or
snowblower, you will notice a lot more knock in a car running on old
fuel. 2-year old fuel with stabilizer is okay for lawnmowers
(probably a bit more smoky) but not for cars. While diesel fuel lasts
longer and there are additives that will make it good for 18 to 24
months, stabilized gasoline for a car better get burned off in under 6
months.
In non-sealed tanks, like on lawnmowers, the lighter solvents
(aromatics) will evaporate away which lowers the octane rating. Car
fuel systems are closed. The gas cap has a pressure-relief valve to
prevent too much pressure building up in the tank when the fuel gets
hot. If the car was left outside to get hot and because of the gas
cap with its relief valve, the aromatics could've evaporated out of
the fuel and been released to the outside. A working gas cap will NOT
let outside air into the tank (so when hot and then later cooled there
could be a vacuum in the tank). If the gas cap is defective, like a
cracked or non-flexible rubber seal or the valve doesn't work then
atmosphere could get into the tank. If the old fuel had ethanol then
it is possible that water got absorbed if the gas cap was defective.
You can't add fuel stabilizer to old fuel to repair deterioration.
Don't bother with an octane booster since most contain tetra-ethyl
lead which could screw up your catalytic converter or oxygen sensor.
Some say they are catalytic safe but I don't trust them. When you
drain the gas tank, be sure to use a pump qualified for transferring
flammable liquids. One spark and BOOM! You could use the old
hose-and-suck siphon method to drain if you don't mind the taste.
Make sure the area is well ventilated or outdoors. Depending on the
capacity of the tank and how much old fuel was left in it, you might
need a LOT of containers approved for flammable liquids.
I'm not sure what you'll want to use that 3-year old gasoline for.
You probably don't even want it in your lawnmower as it is when
drained. You could filter it using a coffee filter and then mix a cup
in at a time with *fresh* fuel into your lawnmower. To recondition
old fuel, filter it and mix 1 part old with 5 parts *fresh* fuel.
Fill the gas tank to 3/4 full with fresh fuel and then top off with
the reconditioned fuel. If there is water in the old fuel, pour into
a glass jug and let the water settle to the bottom, then carefully
pour off the gasoline to leave the water in the jug. Pour the
contaminated water into a tray with sand or cat litter, let sit
outside until air dried and away from ignition sources, and then trash
the sand or cat litter.
