Stale gas, still good?


With the price of gas, I’m bicycling a lot and driving less…so gas sits in the tank a long time…sometime 3-5 weeks or more! Should I use some gas stablizer to keep it from going bad, or would that harm my engine? ( a V-6 chev. S-10, 1999)


Gas stabilizer must be put into currently good fuel, it will not make bad gas good. Definitely put some stabilizer in your truck. I use it in my 79 and it starts up great each summer.


As long as the fuel system is still properly sealed, the gas should be fine.


Gas stabilizer is quite unnecessary in this situation. Gasoline in a sealed system, replaced every month, requires no special treatment. No more than does air stabilizer for your bicycle’s tires.


I only use nitrogen in my bicycle tires. ANd I drink water when I ride it. Coincidence? You decide…


3 - 5 weeks is nothing for gasoline. I would not bother with stabilizer with 3 - 5 months, I would start using it when I knew the gas would be there for over 6 months and certainly over a year. Generally you can get by for up to two years depending on a number of facts, but I consider 6 months safe.

However that is for the age of the gas, not how often you drive it. How long does a tank last you? You might even want to consider not filling the tank, so you will not have to use up a full tank before it goes bad.

Gasoline goes bad not by evaporating, but by chemically changing from smaller to longer chemical chains. For example butane (4 carbons) which is often in gasoline car form into octane (I don’t believe this is a common example, but it can happen) forming octane (8 carbons) that may recombine to form say 10 carbon chains etc. The stabilizer works to slow down this process.

If you are using say half a tank every 6 weeks and refilling then, there is no reason to worry. If you are only driving it a couple of miles every 3 - 5 weeks and refilling it once every two years, then you need to use the stabilizer and I would not “fill” the tank.


Thanks to all yous guys…I didn’t reaize I could learn so much so quick, from so many responces…I’m still wondering whether it would be better to leave the tank full (and avoid condensation) or to, as Joseph suggested, use less in the tank, and refresh it more often? Any opinions?


There are a great many automotive myths. One of them is that a fuel tank picks up condensation. Taint so! Doesn’t occur.

On a cool morning you will find dew condensate on the outside metal of your car. Now lift the trunk and see that the underside of the trunk lid is perfectly dry. Why so? Can you discuss radiation cooling? Will you accept my statement that a sealed fuel tank does not acquire water by condensation.

But back to your little-used car. There is not much you can do that will affect its fuel one way or another. Full tank, half tank, frequent or widely-spaced additions, stabilizer or not – no difference. Your time scale is too short for fuel problems to occur. Do what pleases you the most.


Gas tanks do condense internally. This is why you find a drain in all airplane fuel tanks and it’s a required pre-flight function to drain a bit of fuel into the special tool we use and inspect for water. Water is heavier than gas and settles to the bottom, the inspection tool is a narrow vial that you push up under the drain valve allowing a squirt of fuel into it. you simply look at the vial and if when you see some water settled in it you drain some more untill you see no more water. I must assume that automotive systems aren’t as sensitive as airplanes so this is why the subject never comes up. ( and if your car engine sputters you’re already on the ground ) The airplane is always parked with full tanks to lessen the air space and potential condensation and that system works great at preventing it. Stored fuel WILL condense water in a partially full tank but in cars I guess it makes little difference to function so for aoutomotive purposes it’s a mute point.


I’ve experienced frozen condensate in gas at -30 degree weather in Potsdam, NY (pretty much Canada). Maybe it’s rare, but in my experience, it is possible.

I don’t think I’d worry about keeping the tank full unless it’s winter AND it regularly gets very cold. But in that case, you’re probably not biking to work often anyways. I like Joseph’s plan to keep the tank half full and fill it regularly. Don’t run it dry, though - fill it at a quarter tank. It’s better for the fuel pump.