Does gasoline really go "bad" if you leave it unused for a period of
gasoline degrades over time leading to a number of
problems, ranging from hard starting, to rough running, to stuck
oil, gasoline is a highly refined product brewed to a certain
chemical composition with very specific characteristics. One
characteristic of gas is volatility, a term used to describe how
easily and under what conditions the gas vaporizes so it can be
efficiently burned in your car's engine.
The most highly volatile components in gasoline also tend to
evaporate over time. As they do, the remaining fuel's volatility and
ability to combust properly degrades. The result is diminished
engine performance. Your engine may still start and run, but it
probably won't run as well.
A Serious Problem: Oxidation – Varnish / Gum
Hydrocarbons in the gas react with oxygen to produce new compounds
that eventually change the chemical composition of the fuel. This
leads to gum and varnish deposits in the fuel system.
These deposits and impurities can clog up gas lines and filters, as
well the small orifices in a carburetor and the even smaller
orifices in a fuel injector. Removing these deposits can be
expensive and your vehicle may not run at all or run very poorly
until they are removed.
Condensation can form inside your gas tank and lines from heat
cycling when we store our cars in unheated areas, inside or outside.
Fuels such as E10 or E85, contain ethanol alcohol which increase water
contamination, as ethanol likes to draw moisture out of the
Water, of course, does not work too well as a fuel in an internal
combustion engine. It will cause hard starting and rough running
until it's purged from the system. It can also contribute to
internal rusting of the gas lines and tank.
The resultant scale
and small particles can create a true nightmare, sometimes requiring
the replacement of the gas lines and tank at considerable expense.
How Long Does it Take for Gas to Go Bad?
That depends on a number of factors. For one, it's hard to know how
old the gas you just bought actually is. It may be fresh from the
refinery, or it may be a month old already by the time you top off
your tank. Some gasoline is mixed with better or more oxidation
inhibitors than others.
Want to do?
It's a good rule of thumb to avoid leaving gas in your tank or a
storage container for more than a couple of months.
And if You Can't?
To prevent or reduce water contamination:
You can reduce the chances of water contamination by keeping your
car's gas tank as close to full as possible, especially if the
vehicle is going to be left idle for an extended period.
Or Evaporation of volatile compounds can be limited by making sure
the gas cap is secured tightly. For the same reason, be sure all
portable gas containers are sealed tightly as well.
Draining the tank and lines will reduce but not eliminate water
damage as a dry system can expose the insides of metal fuel lines
and your gas tank to air and moisture, leading to accelerate
formation of rust.
To prevent or reduce fuel oxidation:
If you know gas will sit in your tank or a storage container for
more than a couple months, then it's a wise move to buy some fuel
system stabilizer and mix it in with the gasoline. Run the car
long enough to be sure the stabilizer has gone through the fuel
The stabilizer helps prevent oxidation, the biggie that can turn gas
into garbage that gunk's up your system and leads to expensive repair
Using fuel system stabilizer for extended storage is preferable to
draining the tank and leaving the system dry.
will keep fuel fresh for 12 to 15 months.
If you're going to leave the vehicle parked for and extend period of
time then draining the tank may be the only option even with its