How long does it take for gas to get old? I've been lazy and have half a tank of 91octane mixed with 2 stroke in my car. 3 gallons are about a year old, and 5 gallons are about 3 months old.

 

You should be ok....

A few weeks ago i read something about this. Some dutch organisation filled a drum with fuel 25 years ago and they opened it a few weeks ago, tested it and it was still good. Nowadays the manufacturers mix all kind of stuff through the fuel which causes it to go bad after more then a year and better not to use it then.

 

Fill it with fresh, some decent over-the-counter fuel system cleaner and drive.

 

Whats this mean? Fresh fuel and the cleaner or just the cleaner?
One guy I know says just throw a octane booster bottle in.
Im in the same position as the OP.

 

It's been sitting underground somewhere for 65 million years ^___^ a few years old would still be ok i guess.

 

Yes, fresh fuel with cleaner.
You can add octane booster if you want, but they don't do much. They only raise the octane rating a couple of TENTHS....say from 91 to 91.3.

 

There are a lot of variables involved, but generally fuel will stay good for about a year. You can add fuel stabilizer to help rejuvenate the fuel, but you would need to drain the fuel or at least remove the fuel pump/cover in order to stir in the stabilizer. If your engine is non-turbo then it will probably run fine as-is just as long as the fuel did not absorb a lot of water or corrosion while it was sitting in the tank.

 

No, crude oil has been sitting underground. Refined gasoline is not the same thing.

Fuel stabilizer is not the same thing as octane booster.

 

In my experience between 1 and 2 years is fine. More than that and it starts to degrade and varnish the tank and lines.

 

nobody ever hear of STABIL?(fuel stabilizer)

 

I would personally replace gas and add some fuel injector cleaner in the tank just to be safe cause unless you relieved fuel pressure old gas can possibly keep your car from starting that's what happened to me. Unless all gas is only a month old it should be fine.

 

If the fuel is older than 18 months get new fuel