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Old gasoline

This is more of a heads up than a question. I just had to have a lawn mower engine rebuilt to the tune of $700 because of old fuel. To save you guys some money, it is unwise to trust ANY non-stabilized fuel over 90 days and that is in the winter time. It goes bad faster in the summer. My repair shop said that the 87 octane fuel that we are getting these days is really sorry stuff and of course it all comes from the big refiners. My advice is to stabilize all fuel for mowers, etc. and seldom used vehicles. Stabilized fuel according to the website that I read is good for about a year. None of this surprises me because about 20 years ago ago, a big refiner was caught using paint thinner to boost the octane in aviation fuel. Private pilots started using motor fuels from gas stations because it had less gum than the aviation fuel bought at a lot of airports. And these are the guys that made more money than anybody last year.

I’m curious how the fuel caused $700.00 worth of damage to a small engine. This must be a rider lawnmower or large deck mower? At that price why not replace the engine?

I have run bad fuel on multiple ocassions in various engines and the only result was poor performance and/or the engine would not start.

Why would you not replace a lawn mower engine if it got to $700?

I can’t hardly believe that bad fuel would kill a small engine. More than likely getting it too hot and starving it for oil killed it.


Gasoline goes bad in 90 days? Ruins an engine? I don’t believe a word of your story… except that you got snookered into $700 for an engine rebuild. That I can believe.

I use a lot of bad gas in my lawnmower given to me by a friend that has a boat shop. Three year old gas is pretty bad even when mixed with some fresh. One year old gas is pretty good. I do have to pull the head on occasion to clean the buildup of deposits and have stuck valve problems on really old stuff. All my lawnmowers are free found on trash day and run quite hard on an overgrown field. A little extra work, but it is free gas. Alcohol in gas does make it go bad faster. I take the $700 repair with a grain of salt. Not many people out there really repairing stuff. A friend of mine paid $120 to tune up a chain saw. Whats that, a spark plug and carb gasket!!! I don’t figure my time as being worth much, a better use than posting.


What engine is this??? You can buy a new engine installed for almost anything up to 20hp in the $700 range.

As for bad gas KILLING an engine…I don’t believe it. It may gum it up so it won’t start…but that’s just the fuel line. It won’t DESTROY an engine. Something else is going on here.

What I do for the winter (or summer for my snow blower)…is the last day of use for the year I turn the gas flow off to the engine…then start the engine until it dies…Try to start the engine up again…And keep doing this until it won’t start again…this ensures me that all the gas is out of the engine. The gas in the tank I leave alone. When I use it again next year I just add fresh gas…NEVER had a problem doing things this way for 30+ years.

Thank you for your post. Some time back, certain posts recommended against using a particular brand of motor oil. I immediately put that brand in my lawnmower engine with the hopes that that would kill it. I’m tired of mowing grass. No such luck–the mower didn’t know it was getting a lousy oil. I’ll try some old gas in it, in the interest of science. Maybe the old gas will kill my lawnmower before it kills me. I gave my son an old lawnmower, which he used for a season and then bought a better mower at the yard sale. Three years later, his “new” mower wouldn’t start, so he got out the old mower that had been sitting with old gas for 3 years. It started right up. I once bought an old mower for $15 a a yard sale. It had old gas and ran poorly. I added some carburetor cleaner to the gas–made it a very heavy dose. After half an hour or so, it picked up speed and ran very well. I finally gave it away when I didn’t want to mow any more, but my wife just got me another lawnmower.

In support of the OP’s comment about old gas, I worked at a lawnmower-snowblower shop for a few years and saw firsthand the damage old gas can cause.

I saw lots of carburetors where the gas in them turned to a solid varnish. It was so hard it had to be chiseled out of the carburetor bowl with a hammer and chisel. None of the “off the shelf” carburetor cleaners or sprays would clean these up. They required a long soak in the old 5-gallon bucket of carburetor cleaner (the kind used for automotive carbs for years). That was followed by a carburetor kit and reassembly.

This “extreme” varnish would tend to happen in snowblowers that had their gas left in them over the hot summers. We saw much less of it in lawn mowers that were stored over the cooler winter months.

We don’t know if the OP’s carb had such varnish. If it did, then with labor rates as high as they are today, then it’s possible the OP’s mechanic didn’t want to invest all that labor into an old engine. I don’t think we should be critical of the OP’s situation until we understand how much carburetor the old gas caused, and the repair prices involved.

I believe that you had to have your lawn mower engine rebuilt . . . but $700? Sounds a bit high to me. What type and size of engine was it? Also . . . I appreciate your advice, but I’ve been cutting grass for 35 years, and my mowers are the cheapo Wal-Mart $150 specials. My cheapo mowers last at least 7-10 years . . . and I don’t really baby them, they cut grass and run for an hour or two every two wekks all Summer long. I change the oil twice a year . . . in the beginning of the season and in the middle of the season. I can’t imagine that anyone would leave old gas in a mower when all you have to do is “run it dry” after your last cut in the Fall . . . which I do every year. BTW . . . my mowers usually break the mower deck or something . . . I’ve never had one “gum-up” or engine quit for any other problem. In fact, any gas engine . . like a chain saw, weed wacker or trimmer that I’ve owned, I’ve always just done the normal maintenance, oil change, fuel drain and they run fine. Seems like something more than bad gas caused your lawn mower to go that far South. But your advice is sound enough . . . I’d just add to run it dry on the last cut . . . drain it dry after the last cut . . . or add the gas stabilizer at the end of the season. Thanks for the info. Rocketman

A new carburetor is what? $140 or less if it’s a small push mower. How much should the labor be for the 10 or 15 minutes it takes to put a carburetor on on a Briggs or Kohler?

I know evaporated gas will gum up a carb, but rebuild the engine is a whole other thing.


Depending on the gasoline, some of it can go bad in 3 or 4 months.
What I have trouble with on this story is believing that bad gas caused an engine problem at all. Crudded up tank, filter, or even a crudded up for life carburetor maybe but not engine damage.

If this story about spending 700 on a rebuilt lawnmower engine (must have been a John Deere $) is true then my opinion would be that someone got stuck for 700 bucks needlessly on a very bad misdiagnosis.