The Effects of Gas in Your Tank Over Long Periods of Time

Does gas get old? This question is debated in many a garage. Recently, I wrote a post on storing your classic car for the winter. Keeping gas in your tank over a long period of time is a cause for concern. There are some actual chemical changes that happen to gasoline over time, but some issues can be fixed with a fill-up of fresh gas. Make the best plan for the least amount of fuel damage.

STA-BIL Storage Family Shot

Adding a fantastic product like STA-BIL® Fuel Stabilizer will help keep your fuel fresh even if it’s stored for up to a year. It works with all types of gasoline and it eliminates the need to drain your tank before you store your vehicle.

First, you will need to fill up your tank and add the STA-BIL® Fuel Stabilizer, drive your car for a little while to circulate the product and get it into your carburetor or fuel injectors. STA-BIL® Fuel Stabilizer will protect any steel or aluminum below the fuel line from corrosion.

Loss of Volatility

The most common issue with old gas is that it has lost many of the volatile compounds. These compounds are the first to evaporate, but they are also the most powerful components when ignited in your engine. Using up your old tank of gas before adding new gasoline can have a reduction in fuel efficiency for the remainder of the tank. Three things can help prevent this from becoming a big problem. If you add new gas before driving, this resolves much of the problem. Second, make sure that you leave your gas tank full when you aren’t using your car. Less air in the system gives these compounds less space in which to evaporate. Third, make sure your gas cap is tight and there is no place for an exchange of air.


Air plus time along with the metals in your fuel system can cause oxidation. This means that the hydrocarbons in the gasoline will change because of their interaction with the oxygen molecules. The change will result in varnish or gum that will require a cleaning compound to remove.


fuel tank leakAnother issue with a leaking fuel tank is the addition of water. Added water can cause incomplete combustion of gasoline and lead to several problems. If there is enough water, your gasoline will not ignite. This can cause irregular ignition and foul spark plugs, rust the metals in your fuel system, destroy the lubrication of fuel injectors and clog lines.

To keep gasoline from becoming a problem when unused, make sure the fuel system is clean and intact If dust or dirt isn’t present to change the fuel’s chemistry, you won’t have issues. This is also true for holes letting in water and oxygen. Second, plan ahead. This is true whether you are trying to drive a car that you have purchased with an old tank of gas or if you’re putting a car into storage.

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