View Full Version : How soon will gas go bad?

07-13-2005, 09:53 AM
I've recently had to dump out about 20 gallons of gas from last season. I opened up a discussion in craigslist automotive forum about this and got some interesting answers.

One guy says:

who told you this? gas mixed with oil < autotek > 07/13 08:28:56

has a shorter shelf life than raw gas.It is good for at least a year.Raw gas is good for many years.

Can you comment on this? If this is correct, then I think I'd buy gas and not mix in oil until I'm ready to use it... (In the past I mix in oil right away while I have memory of how much gas is added)

07-13-2005, 10:22 AM
Complete BS. Gas will get stale and start causing combustion problems after 2 months. Adding oil will have no effect on the rate of oxidation. The rule of thumb is to add fuel stabilizer if the gas will not be used up over a period of 1 month. It's best to ALWAYS add fuel stabilizer every time you buy fuel.

Stale gas causes more outboard failures than just about anything else. It results in carb jet blockage, stuck floats, stuck rings, cylinder deposits, and in 4-stroke engines stuck valves that burn out. If you store fuel for longer than 6 months, the octane rating also drops and you can add pre-ignition and power loss to the list of bad things.

With the proper dose of fuel stabilizer, you can store fuel for up to 1 year. I'd still add an octane booster to fuel stored for that long before use.

07-13-2005, 10:57 AM
Right on Doc!

The speed at which gas goes bad depends, in large part, on how it is stored. Gasoline stored in plastic containers gets "stale" quicker, as does gas stored in direct sunlight or if it's permitted to get "warm."

Gas goes "stale" from the evaporation (and/or oxidation) of volatile hydrocarbons. When it goes "stale," the result, generally, is a loss in octane - and the gas will usually smell "sour." Of course- when the volatile compounds are gone - the fuel tends to get more "gummy." If you can't dump the fuel - belnd it with new gas - should help somewhat.

Also - if you add a fuel stabilizer - be certain to run the equipment after you add it - in order to make sure the stabilizer is present throughout the fuel system.

I guess if you stored gas in a vapor-tight container in a cooled environment (fridge) it would last that long - but your beer would have to go to the shed and who wants warm beer? :P


07-13-2005, 02:49 PM
Is fuel stabilizer effective if the gas has been sitting for about one month before adding? I filled up the tank about 3-4 weeks ago and did not put any stabilizer in at that point thinking I would go out again soon. I've been so busy at work looks like it may be a few more weeks before I get out and use some of that gas.

07-13-2005, 03:22 PM
Adding stabilizer after 1 month will help since it contains detergents and dispersant that will get some of the gunk that might have formed into solution. I will slow the further degradation of the fuel.

Some company sells a product that is supposed to "wake up" stale fuel. But I can't remember the name. Check out a few boating catalogs on line and see if you can find it. Look under fuel additive.

07-14-2005, 10:09 AM
another 2 cents worth. i have been told to use aviation gas if not going to use it for a while as it does not go bad and also to spray marine fogging oil into carb. till engine starts to smoke and this will remove moisture and oil the valvle stems ,springs and whatever

07-15-2005, 04:45 PM
What brand of fuel stabilizer do you use or recommend?

07-15-2005, 04:50 PM
It's called stabil (sp)

07-15-2005, 05:04 PM
Thanks Wayneo

07-15-2005, 05:12 PM
You have to be careful with AVgas. Most of the aviation gases still have lead in them. Since most watercraft don't use catalytic converters you shouldn't have any problems using leaded fuel. Now if you use AVgas in your auto then you're going to destroy your cats and O2 sensors with the lead.

07-17-2005, 09:17 PM
It's called stabil (sp)
So much to learn ??? do you put the whole thing in ::)

07-17-2005, 11:20 PM
You follow the directions Chick. They're on the bottle. ;)

Don't use aviation fuel in an outboard. While it's true that you can store it a little longer, you will actually loose performance with that octane level. I recommend Chevron mid-grade (89 octane) and Stabil to anyone who will listen.

Fogging an engine is a good practice if it will not be used for several months. For shorter periods of inactivity, just use Stabil and run the fuel out of the engine to prevent gum formation. Fuel allowed to evaporate in a carb or fuel injections system will form gum regardless of the stabilizer.