Can Gas Really Go Bad?

Does gasoline really go “bad” if you leave it unused for a period of time? Some people are convinced this is just another urban legend, and that people who worry about “old gas” and spend money on stabilizer are wasting psychic energy as well as cash.
But in fact, gasoline can degrade over time, which can lead to a number of problems, ranging from hard starting and rough running, to not starting at all.

Here’s why

Unlike crude 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 efficiency burned in your engine.

The most highly volatile components in gasoline tend to evaporate over time. As they do, the remaining fuel’s volatility and ability to combust properly degrades. The less volatile the fuel, the less effectively it burns in your engine. The result is diminished engine performance. Your engine may still start and run, but it probably won’t run as well.

Sometimes, it only takes is getting rid if the old gas and putting in fresh gas to run well again.

When the volatile components in the gas evaporate the hydrocarbons which remain 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 as the small orifices in a carburetor and the even smaller orifices in a fuel injector. Removing these deposits can be expensive and your engine may not run at all or run very poorly until the are removed.

Evaporation of volatile compounds can be limited by using a gas stabilizer, which should be used in a portable gas container right from the pump so it doesn’t go bad while waiting to be put in the machine. In addition make sure the gas cap is securely tightened, both on the machine and the portable gas container. Remember gas goes bad quicker in hot weather.

Water contamination

Condensation can form inside your gas tank and lines from heat cycling. Fuels such as E85, which have a high concentration of ethanol alcohol, may be even more susceptible to water contamination, as ethanol has a tendency to draw moisture out of the surrounding air.

Water contamination can be a problem at gas stations with light traffic due to a slightly different kind of heat cycling. The underground storage tanks experience increases and decreases in temperature. This can cause moisture to form and contaminate the fuel. When you fill up at such a station, you’re plumping water along with gas. Such low-traffic stations may have other contaminates in their underground storage tanks, such as rust. They are best avoided when possible.

Water, of course, does not work 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.

You can reduce the chances of water contamination by keeping your equipment’s gas tank as close to full as possible, especially if the equipment is going to be left idle for an extended period.

How do you identify bad gas?

One way is to eyeball it. Oxidized fuel often turns darker over time and may even smell sour. You can check stored gasoline by pouring some into a clear gas container and comparing side-by-side with known fresh gasoline. If your old sample looks noticeably darker than the fresh gas, you have strong evidence the gas has gone bad.

How long does it take for gas to go bad?

That depends on a number of factors. Age: 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.
Quality: Some gasoline has better inhibitors than others. Air temperature: Gas goes bad quicker in hot weather.

It’s a good rule of thumb to avoid leaving gas in your tank for more than a couple of months, and a storage container for less time. The higher volume of gas, the slower the rate of evaporation.

If you know gas will sit in your tank or a storage container for a long period, then it’s a wise move to buy some fuel system stabilizer and mix it in with the gasoline. Do it before you put the vehicle into long-term storage or before storing your lawn equipment fuel containers for any period of time. The stabilizer helps prevent oxidation, the biggie that can turn gas into garbage that gunks up your system and leads to expensive repair work.

Using fuel system stabilizer for storage is preferable to draining the tank and leaving the system dry. This can cause rubber hoses, gaskets and seals to dry rot and crack, possibly leading to leaks and even a fire. In addition, a dry system can expose the inside of metal fuel lines and your gas tank to air and moisture, which can lead to or accelerate the formation of rust.

Fuel system stabilizer is not a cure-all and it doesn’t last forever. It must be mixed with fresh gas before the equipment is stored, not added to already old gas. It can slow down the oxidation process and keep gas fresh for as long as 12 to 15 months. If you’re going to leave the vehicle parked for longer than that, you may want to drain the tank and refill with fresh fuel before returning the vehicle to service.