When is "old gas" too old to use?

[MetroMPG]

An article on Autospeed got me wondering about this.

I was surprised to read the experts giving answers that were much shorter than I would have expected.

Depending on whom you ask, gasoline is good for ...

• 6 months - in a sealed container, after which it starts to degrade
• up to 12 months in a sealed container
• "several months" old fuel in your tank risks fuel system problems
• "several weeks" is enough to detect octane degradation, based on dyno testing

Read more from: The Life of Fuel - How long does fuel last in your car's tank?

When I got the Firefly, it had been sitting, the tank nearly full, for seven years. The engine started normally on the old gasoline, and it ran apparently fine when I test-drove it around the block.


7 year old gas

7 years seemed pretty extreme, though, and I was warned that old gas could gum up the intake valves and make them stick. So I drained the fuel tank to nearly empty, drove straight to a gas station and filled up with fresh gas before driving it home.

OK, so if 7 years is too much, how about four years? That's how old the gas is in this 1990 Swift GTi:


4 year old gas

... and with a boost, it started right up after sitting in a field for that long.

On the other hand, I have had trouble running a 2-stroke boat motor with fuel that was 2 years old. Maybe it depends on the engine, or the oil mix causes things to go wonky sooner.

Autospeed: The Life of Fuel - How long does fuel last in your car's tank?

[Daox]

I have a 1993 Toyota Tercel sitting in the driveway. I know the gas is at least 4 years old. I fire it up a few times a year to keep things oiled. Never has any issues...

[gone-ot]

...my lawn-mower sits all winter, and seems to start OK each spring.

[Ryland]

Most modern cars have sealed gas tanks so very little fuel vapor leaks out, they also have fuel injection so there is little to no air in the rest of the fuel system.
Motorcycles that have gasoline that is 9 months old or more tend to have issues because there are so many vents in the carburetors and the gas cap is more or less an open vent, because of this the volatile part of the gasoline evaporates and escapes leaving behind varnish, this is often made worse with ethanol in the gasoline because the alcohol sucks up water out of the air the ethanol then easily evaporates leading to water in the gas.

So I figure if gasoline is in a can or tank that is vented it has a shelf life of 6 months before issues start to show up, if it's sealed in a safety can, or the gas tank of a vehicle with fuel injection it's good for a year or more.

The motorcycle shop that I used to work part time at has a lot of motorcycles come in every spring with bad gasoline and I still get calls from friends who have lawn mowers that have year old gas from a gas can put in them and don't want to run, change the gas and they run, put that old gas in a fuel injected car and it will run as well.

[Thymeclock]

Originally Posted by Old Tele man

...my lawn-mower sits all winter, and seems to start OK each spring.

I store quite a bit of gasoline in proper 5 gallon storage containers. I've had some of it for up to 2-3 years, still usable, with no bad effects. The worst part is that some of the volume will be lost to evaporation, no matter how you store it.

Gasoline contains additives. If you are going to leave gas in a snow blower or lawnmower, either drain the tank completely (preferably) or keep it entirely full. Gasoline contains additives. If you've ever had to rebuild a lawnmower carb you might find it full of goo from someone who left it sitting for several years with gas still in it. The gas evaporates and leaves a lot of residue that clogs the carb.

[MetroMPG]

That must be why several old-timers that I know with outboard boat motors will disconnect or shut off the fuel line to the engine -- while it is running -- several minutes before they plan to stop it. Then let it run out and stall when they've docked, with the carb dry. They do this if it's going to be sitting even for a week or more.

[darcane]

My 1968 Chevy pickup had gas in it that was about four years old. It ran just fine, but the filter clogged pretty quickly. No sealed tank here.

I've since drained the rest of the gas out until I can more regularly drive it.

[Clev]

Originally Posted by MetroMPG

That must be why several old-timers that I know with outboard boat motors will disconnect or shut off the fuel line to the engine -- while it is running -- several minutes before they plan to stop it. Then let it run out and stall when they've docked, with the carb dry. They do this if it's going to be sitting even for a week or more.

I've known of several cars that ran fine with 4+ year old gas in the tank. On the other hand, we run our outboards dry as well. (It's amazing how long a Honda 5 hp 4-stroke will run after you disconnect the fuel line.)

[Ryland]

The issues with old gas include varnish and varnish flakes that clog up jets in smaller engine carburetors, so a 1.5L carburetor is going to clog up more easily then a 6 litter engine on a truck would, so a string trimmer is going to be fussy while a tractor might not be, and on something like a 2 stroke out board engine that is sensitive and will burn a piston if you run it lean it's best not to risk a partial clogged carburetor, where an old single cylinder John Deere tractor doesn't even care if there is water in the gasoline.

[Thymeclock]

Originally Posted by MetroMPG

That must be why several old-timers that I know with outboard boat motors will disconnect or shut off the fuel line to the engine -- while it is running -- several minutes before they plan to stop it. Then let it run out and stall when they've docked, with the carb dry. They do this if it's going to be sitting even for a week or more.

Exactly. I'm "on the wrong side of fifty" and I always do this with my snowblowers. They are 50 and 40 years old, respectively. (I bought both of them used and have had each of them for "only" about 25 years.) One had a gas tank that was full of rust and crud when I got it, and I had to put a replacement tank on it.

Some winters are mild and you might only need to use the blower a few times. No matter. I installed a shut off valve in the fuel line and let it run until stalling out whenever I use it. Then I empty the gas tank fully at the end of the season. With the lawnmower I only empty the tank out when putting it away for the winter. You'll never go wrong in doing that.