View Full Version : What happens to old gasoline?

05-29-2002, 11:47 AM
I have an old pickup truck that I'd like to revitalize. The gas tank is more than half full, but the gas has been sitting in there for more than two years. Is the gas still good? should I shake the truck to maybe mix it if contents have settled? Would adding new gas help at all?

05-29-2002, 01:25 PM
You may have lost some volatile components of the gas, and it may have absorbed some water. So it wouldn't hurt to fill the tank and add some gas-line anti-freeze stuff to remove the water.
It may run poorly for a tank or two. You may have to clean the plugs and do some other random engine maintenance to get it to run well.

Here's a corollary question. I have a few 2-cycle appliances (weed whacker, etc) that require an oil-gas mix. The instructions say to use the oil-gas mixture before a certain amount of time (a couple of months). What happens if I don't? And if I have to discard the gas/oil mixture, what do I do with it?

05-29-2002, 01:27 PM
I wouldn't recommend mixing up the contents of the gas tank. After two years, there's bound to be some water (from condensation) in the bottom of the tank. You want to avoid getting that water in your fuel line. (Auto gas tanks have a "low point" below where the fuel line enters the tank, to trap water and sediment.)

I've never heard of a shelf life for gasoline. The components of gasoline (octane, benzene, toluene, etc, maybe some ethanol) don't separate, as far as I know.

05-29-2002, 04:14 PM
I'm not a chemist, but yeah, old gas loses its volatility. Is there a way to drain your tank? Kamandi is right in that there may be too much condensation that has occurred in the tank.

05-29-2002, 04:39 PM
Old gasoline can deteriorate and get gummy or turn into "varnish". I've had it happen to an old motorcycle. I had to disassemble and clean the carburetor whenever I tried to restart it, the gasoline that was left gummed up the works.

That's why there are products like this (http://www.amsoil.com/products/ast.html) It is likely that you will need to clean out the carb before the thing will start again. If you can drain the tank and put in fresh gas, that would be best. I'm not sure if old gas is bad outside of the whole gumming up factor, but it does change over time.

05-29-2002, 05:25 PM

The EPA has some tips on how to "recondition" that old gas. IT requires draining the tank though. the recommend a 5:1 new gas/old gas mixture, which is kind of tough since the tank is half full. I'd try some octone boost and new gas. Then don't let the tank go below 3/4 tank, just keep adding new gas. Not the optimal solution, but the other solutions all involve removal of the gas. That's a pain in the butt. If the truck is carborated rather than injected life is a little easier, just get a few cans of carb cleaner and spray the heck out of it.

This is by no means the correct approach, it is the lazy ass approach a.k.a. probably good enough to work approach. If you are considering fully restoring the truck, I wouldn't do it this way. If you are looking for a beater to bang around with this may be your approach. I might also be wary of dried out gaskets, seized rings, deteriorating hoses if the thing has sat for a while.

Johnny L.A.
05-29-2002, 06:15 PM
You know what they say: "There's no fuel like an old fuel!"


05-29-2002, 06:28 PM
...and I'll vouch for my old buddy :) cheesesteak. I had a damaged motorcycle that sat unattended for about a year. When I pulled the tank, the gas was mostly water (condensation) and rust and goo. New filters and carb cleaner. I would NOT mess with whatever toxic waste is in your vehicle now. Siphon it out (with a PUMP, and don't smoke while you're doin' it - disclaimer) and start over. I'd spring for a new filter and the line cleaners mentioned above. It could save you a lot of heartache in the short-term.

Doc Nickel
05-29-2002, 08:36 PM
Actually, most of this is good.

Gas doesn't "go bad". It simply loses some light fractions due to evaporation. Which is reduced greatly if the filler cap is in place and closed.

The condensation can be a problem, but if it's a fairly modern car, with a charcoal cannister type tank-vapor recovery, or better yet an injected car, you won't have too much trouble. Especially if you live in a fairly dry locale.

All I'd do, if I were you, is buy some fresh gas (in cans, don't drive the car anywhere just yet) and a can of Iso-HEET (isopropyl alcohol) type fuel line dryer. (The Iso is friendlier to rubber lines and seals than the methanol type.)

Dump in the dryer then the new gas- just the pouring will mix it all well enough.

Then drive the car normally (assuming you don't for some reason have a huge slug of water in there) 'til it's down to less than a quarter tank before you refill.

For a typical car that's been sitting with the gas cap on and the fuel system in working condition, for less than, say, three to five years, that's all that's necessary.

05-29-2002, 08:53 PM
Thanks for the info, folks! I just want to use the truck as a beater. I guess the wise thing to do would be to drain the tank as much as I can but lord knows what I'd do with the old gas. Doc Nickel's method sounds more appealing since I wouldn't have to worry about what to do with the gas. The cap hasn't been touched since I parked it, so maybe that's a good sign.

Enola Straight
05-29-2002, 08:57 PM
I second the recomendation for isopropyl alchohol as a gas line

Methyl merely creates methyl-water and methyl-gasoline layers
in the tank. Isopropyl fully mixes, creating a homogenous
water/alcohol/gasoline mix.

Fill that tank up with as much isopropyl as you can find.

05-30-2002, 11:07 AM
Originally posted by Enola Straight
Fill that tank up with as much isopropyl as you can find.


The tank's half full. Are you recommending to fill it the rest of the way with isopropyl alcohol? You'll end up with half gasoline, half isopropyl alcohol (and a little water). Is that what you're saying? Will a truck run on such a mixture?

05-30-2002, 12:01 PM
You stand the chance of gumming up the lines. If I went through the trouble of fixing up this truck I would drain/disgard that gas.

Just my humble O

Doc Nickel
05-30-2002, 03:41 PM
As long as the gas cap's been on the whole time, there's little or nothing in the tank to "gum" up anything. Presuming young malcontents haven't intentionally dropped water/sugar/dirt/rocks in while it was sitting, the worst you can expect is a little water from condensation.

And too much alcohol "dryer" is not a good thing- it'll burn, but at half the BTUs of the gas.

A 12-oz can of fuel line dryer (either iso or methanol alcohol) can "soak up" close to half it's volume in water (or so I'm told.) And I'd be VERY surprised if you'd gotten six ounces of water in there just by condensation. Just plunk the one can in, and top it off to "full" with fresh gasoline.

I've "resurrected" junkers or long-parked vehicles in precisely the manner I described above, and occasionally had the need or opprotunity to remove or service the tank out of others.

Several years ago, when I pulled the tank from a '65 Corvair that had been sitting (in Alaska) since 1977, the two gallons of gas we poured out of the tank were a little dark and cloudy, but ran a little Briggs & Stratton lawnmower just fine. There was no visible water- the cloudiness probably indicated a little, but there were no "droplets" to be seen, and no rust.

Enola Straight
05-31-2002, 01:13 AM
Originally posted by Kamandi


The tank's half full. Are you recommending to fill it the rest of the way with isopropyl alcohol? You'll end up with half gasoline, half isopropyl alcohol (and a little water). Is that what you're saying? Will a truck run on such a mixture?

A few years ago, a neighbor's 8 year old kid decided to "Gas up"
my car with the garden hose.
I drained what I could and loaded up with isopropyl.
It ran a little slow for THAT tankload, but was fine as soon as
I filled it up with gas again.

05-31-2002, 11:04 AM
Now I'm curious--back when Y2K was approaching, I thought I had learned from many reliable sources that gasoline only has about a 3-6 month shelf life, and that you couldn't really store a lot of it in advance (as you can with diesel, which is more stable). Is this all just a load of crap, then? Should I be out there buying a few hundred gallons of gasoline now as a hedge against when the prices spike?