I have been intrigued by conflicting information in this NG regarding the
degradation of gasoline over time.
This is what Chevron has to say on the subject and this makes good sense.
22. How long can I store gasoline without it going bad?
Gasoline stored in a tightly closed container in a cool place will stay good
for at least one year. It is better if the container or fuel tank is almost
(95 percent) full. If the container or fuel tank will be in the direct sun
or will be heated above 30°C (80°F) much of the time, add an aftermarket
fuel stabilizer to the gasoline when you first buy it. Gasoline-oil blends
for two-stroke cycle engines stored under the proper conditions will keep as
well as gasoline itself.
Someone like Chevron has to give conservative advice, since they don't
want anyone claiming engine damage etc as a result of the advice.
The only petrol I've had go so bad that the engine wouldn't start is
two-stroke stored in small fuel tanks in things like chain-saws and
It has taken probably >3 years of non-use for this two stroke fuel to
go this bad.
Stored in larger tanks and larger quantities and just normal fuel (not
two-stroke mix) I've never had fuel go bad so the engine wouldn't
start, and I've left some cars for years with the same fuel in the
tank/carby bowl. One tow car I own hasn't actually been refueled since
2002 and it still started just fine the last time I started it about a
Obviously if you follow the Chevron redcommendations, which btw are
similar to the instructions you will find in an outboard motor manual,
then you don't have any fuel trouble.
If you don't follow the recomendations then you empty out the bad
fuel, add good fuel, and the thing usually then starts promptly.
I've started old lawnmowers I own (mower kept as a spare) many years
after the last use, and all the old fuel had actually evaporated away,
and with fresh fuel and maybe blow out the carby bowl with compressed
air they are soon running again as good as new.
(To get email address ROT 13)
Whatever about Chevron's advice, I had a Harley that sat for about 1.5 years
while I went overseas. I came back and it wouldn't start to save my life.
Drained the fuel, added fresh and it started right up. I'm a believer
that without stabilizer, fuel does go bad quicker than 3 years.
Exactly! You would expect them to say that gas goes bad in a few months so
that no one sues them claiming they followed their advice and 1 year old gas
ruined their car.
Think about it; you have backwards.
The question just above it on the Chevron website, about premium gas, is
interesting. I have a friend who kept careful records for several years and
is convinced that premium gives him 10% better mileage than regular. Just
goes to show that anecdotal evidence is inaccurate, cause all authorities
say he is wrong.
It's entirely possible. If you have a car that requires premium and the
computer is adjusting (retarding the spark or whatever it does) to avoid
knock on lower grade gas it could impact mileage. This will be affected by
how the car is driven and how much its being put in situations where these
compensations are being made. Years ago I had an old hand-me-down Pontiac
that should have been getting premium but I used regular and it would knock
on heavy acceleration.
A tank that is not perfectly sealed will exhale gas as it warms and inhale
air as it cools, along with water vapor which condenses. Keeping it full
reduces the volume of air exchanged when this happens, and shading it
reduces the amplitude and frequency of temperature changes.
Check a few motor manufacturer sites Sthil recommends not using gas
more than 30 days old. Who cares what Chevron says, they sell it but we
have use it and know it lifespan. Plastic containers do allow minute
amounts of gasolenes components to leach out. You can smell bad gas, it
does not take it that long to go stale. Chevron wont pay for that
clogged up carb, you will.
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