Stale gasoline

How long does it take for unleaded gasoline to become stale? The reason I ask is I have a very large tank that, apart from occasional top ups to avoid condensation forming, the same gas or most of the same gas might remain in the tank for thirty days or more. Are fuel stabilizers useful in this case or just good for longer term storage?

30 days is nothing. Once you get to 6 months start thinking about fuel stabilizers

Ditto to what Cig said. Although I would have said a year, but 6 months is a good rule of thumb too.

Gasoline in a properly sealed container stays fresh for a very long time. I have restarted cars that sat idle for two years without stabilizer and then drove away normally, no added fuel.

But there are many folks who are huge fans of fuel stabilizer. Especially boaters. Some insist on adding fuel stabilizer with each fill-up. I’m sure you will hear from them.

As for topping up to avoid condensation, don’t. A properly sealed tank will incur little condensation, if any. Instead, let your tank run low and then fill up with fresh fuel.

Thanks Steve and others for responding. By the way, as I’ve heard this can be hard on the fuel pump how low is low?.

Over time, gasoline does indeed degrade…Much depends on the gasoline itself…All gasoline is NOT the same…If you are lucky, you might get a straight-run distillate, pure, naturally refined gasoline…But today, much gasoline has been processed by a method called "Alkalization and Catalyzation "…Cat Cracked for short…Using this process, they can literally make gasoline out of asphalt…It’s this cat-cracked gasoline that’s unstable and given enough time (at least 6 months) it starts to revert back to the heavier elements it was made from…Like any chemical reaction, high temperatures speed this process up…It changes color, from almost clear to orange then to burnt orange then brown. it smells like old turpentine…

You ask how low is low? Don’t start! We have this discussion regularly and there is never a consensus.

I have suggested letting your tank run low merely as a practical means of using up the old fuel and replacing it with fresh stuff. I am not advising you to try to scrape the last dregs out of bottom of the barrel. Your own judgement should be sound enough.

As others say gas will “keep” 6 months or more.
But when I bought a “new” car and still had the “old” car around for about a year I drove the old one very little.
I drive a total of ~4000 miles a year.
I didn’t fill the old car for several months and wound up with “summer” gas in the winter and it made for hard starting.
Refilled the tank and all was well.

I’ve had gas in one of my cars for a year and no problems. The thing with condensation in the tank is that it is the temperature change of the air inside the tank that causes condensation. At the air temp gets lower, less water is able to be held in the air and the water is squeezed out of it and into the gas. The more air in the tank, the more water can condense.

If I think it might be 6 mos to a year before I’ll use up the fuel I add stabilizer soon after purchasing it. For instance lawn mower gas purchased in the fall. In your case I’d only use stabilizer if I was going on an extended vacation.

In your situation, I’d let my gas tank get down to about 1/8th tank once a year. Then when you fill it you’ll have purged out virtually all the “old” gas.

My son inherited a lawnmower from my wife’s parents’ estate. He then had a neighbor who moved and gave him a better mower. The mower from my wife’s parents’ estate sat for 2 years with gasoline in the tank. When the mower his neighbor gave him quit, the mower that had been sitting for 2 years started with the first pull of the starter cord.
When the inherited mower finally gave up, my son bought an engineless reel type mower. His wife says it takes quite a few pulls on my son’s starter cord to get him running and out mowing the grass.