Bad fuel messed up valves?

[HawkRod]

So I have had a strange sequence of events and wanted to post about them here and see what the FBBO brain trust thinks...

Background: I have owned a 15 HP Exmark Lazer Z industrial walk behind mower for 22 years. The mower has been flawless for all those years with zero mechanical issues - just regular maintenance.

Separately, I drained 7-8 year old, rusty, varnish smelling fuel out of an old car. Old fuel is hard to get rid of here, so I filtered it and ended up with about 4 gallons. I decided to run this fuel in my mower, mixed about 50/50 with fresh fuel. (I figured if I gunked up the carb I could easily and quickly rebuild that.)

After 2-3 weeks (? don't remember how long exactly), when I started the mower, only one cylinder was running. It had dropped a pushrod because the intake valve stem was "sticky" and the small springs couldn't push the valve closed. I loosened the valve up by pushing it up and down a few times and reinstalled the pushrod. It ran fine until next time I started it. Same thing. After a couple of weeks both intake valves were getting sticky and dropping pushrods. This went on all summer as I resigned myself that I had to rebuild or replace the engine in the winter...
...then I used up all the old fuel mixture.

About two weeks into using only fresh fuel, I was able to start the mower without dropping a pushrod. The sticky valve issue appears to be gone; the mower has continued to start normally.

I have never experienced anything like this, but it certainly appears that the old fuel caused the intake valves to get sticky with a tar like substance on the valve stem - looked like old molasses. My best guess here is that the old fuel, when contacting the hot intake valve stem, coated it and caused it to start binding (the exhaust valves never had issues).

Now it goes without saying that running old fuel is not good to do - I get it. But I have "used up" old fuel like this before, but never had an issue like this. If nothing else, I will now be super cautious about running old gasoline!

Appreciate any feedback or experience folks have had. Any horror stories about using old fuel?

 

[66Newport]

Getting rid of old gas sucks and you don't want just dump it so I understand your approach to burning it in small engines at 50/50. I do the same but dilute to at least 3 parts gas to one part old gas to be safe. If it is milky though, you have to get rid of it some other way. I gave away 20 gallons to a guy that burned it in a shop stove. Catch was I had to deliver it a few miles to him. I was ok with that.

And yes, old gas will stick to valves and gum them up. My 383 was all stuck up when I got it due to the bad gas run through it. When I smell that distinctive smell of old gas, I think of the time when I pulled that engine apart and fixed it.

That's why it kills me to see people doing the "will it run' with old barn-find cars; they check the motor turns, and that there is oil and a good battery, then boom right for the key.. No.. check for old fuel first. It will bite you.

 

[WileERobby]

Never used old fuel in anything, never will. Fuel is like bread, If it ain't fresh... it's stale.

 

[493 Mike]

Hell, you live in Pennsylvania, can't you pour it on the ground and send it back to the state oil reserves?

 

[R413]

Just don’t do it. It’s bad fuel so get rid of it. You can damage good engines this way. Cost you real $$$

Now along the same lines don’t get paint on your valve stems on the engine. So tape over or put a paper towel in the ports on the engine. Don’t get paint inside the top valve spring area with the valve covers off either.

 

[Don Frelier]

I had a fair amount maybe 4 gallons that had water in it.
I literally dumped some of it into an old gas tank cut in half and lit it by flicking a match into the open fuel.

I started small but got more and more aggressive until I had a 6 foot tall fireball.

Didn't take long and it was all gone.

 

[PlymCrazy]

In the cars I try to keep the fuel as fresh as possible. Daily drivers are easy but the older, less driven ones, can be a little trickier.

(2) years ago we acquired a jet ski from my BIL that had been sitting for 18 years in his garage.
My son and I drained about 10 gallons of old gas out of it.
We put the old gas into five-gallon buckets and put lids on them.
We then put about (2) gallons of fresh gas in the ski so we could attempt to start it after we got the motor to turn.
We did get it running.
But then it sat with that fresh gas for another (2) years.
Until about (3) weeks ago.
We decided to finally put the machine in the water for the first time in (2) decades. We got it running on that (2) year old gas for a minute or so and then shut it down as it’s not supposed to be run long when not in water.
So we topped the tank off with another (12) gallons thinking that the old gas would mix with the new by the time we got to the lake to put the ski in the water. Well, for the first (30) minutes or so running it on the lake it spit and sputtered and then finally ran perfectly for the next (2) days.
At this point I’m chalking the “spitting and sputtering” up to the machine burning up that bad gas that was in it.
I’m guessing it didn’t mix well with the new gas as I originally thought it would.
All I can do is speculate at this point.

And finally…we emptied those (2) five-gallon buckets into our burn pit this summer. Very surprised at how well it lit. Startling actually.

 

[moparwacko]

My Father in law would routinely park his garden tractor in the fall, and every spring would have to call the local Cub Cadet dealer to come get it. He always scoffed at me using ethanol free in everything but our modern cars. Gas is gas is what he said, no matter how old it is. Well, the last year before he passed, it cost him a new 23hp Kohler. The exact thing Hawk described, valves burnt, sticky varnish everywhere before it went boom. That tractor was only 8 years old with less than 400 hrs.

 

[R413]

If you have 1/4 tank of bad gas, then you fill the tank with new gas. Now you have a full tank of bad gas. It takes a lot to dilute it down. Not worth it.

 

[EARLY B]

Makes great weed and bug killer.

 

[5wndwcpe]

Any old gas I have gets mixed with used oil and, ahem, donated to Walmart.

 

[68_661charger]

Yes had the same thing happen to my slant 6. Mixed new fuel with the 12 year old gas that the six was running on and bent a pushrod backing out of the driveway. I took the valve spring off and sprayed brake cleaner around the stem to loosen up the stickiness and drained the tank like I shouldve done in the 1st place. All is well now.

 

[bandit67]

Hawk, I done the same thing. Pulled old gas out of a car and put it in my Kolher twin motor on my zero turn. SOON, I was down to one cylinder. Seems detonation set in and I lost a pushrod down in crankcase. It's still there. Ok, here's how i see it. Old gas will run, just poorly, maybe causing gumming up, but does not seem to cause instant detonation UNTIL some 'fresh' fuel is mixed with it. Then all kinds of trouble can occur. So, rule is , if it is pumped out of a tank cause it's old, it is disposed.

 

[HawkRod]

Thanks for all the comments and responses guys.

Obviously, I know it is not good to run old gas, but I figured that it would potentially only lead to a carb rebuild, which I wasn't worried about. I never would have guessed I'd have valve issues from the crap gas...

Live and learn!

Yeah, from now on, old gas will either be a bonfire starter, allowed to evaporate, or turned in to the hazardous waste collection centers. It will no longer be burned in any engine!!!

 

[Bennoel 10]

Came across this thread and thought wow never really thought about this. So my question is how long do you consider old....1/2 years ? Coincidently a close friend called me last week and explained his freshly built big block hadn't been started in over one year . He had health issues and couldn't mess with it. Fast forward and healthy now , starts engine, fires quickly. Runs for a couple or three minutes then starts to miss fire and back fire . Sounded like possibly bad plug or so. Anyway haven't had a chance to go over and look but kinda curious if it could be bad gas and now much more serious. Any suggestions or procedures recommended greatly appreciated.

Thanks

 

[HawkRod]

So my question is how long do you consider old....1/2 years ?

That's a good question that I don't have the answer to. Many would tell you 6 months and fuel is old. Personally, I feel like fuel likely degrades linearly over time as it gets older, so I don't think there is any sudden "cliff" that puts it over the edge so it becomes dangerous to run. I have run cars with year old fuel and detected no issues, but that doesn't mean it was wise to do. Personally, I'll let my nose tell me. If it smells remotely bad, I'm not going to use it.

Coincidently a close friend called me last week and explained his freshly built big block hadn't been started in over one year . He had health issues and couldn't mess with it. Fast forward and healthy now , starts engine, fires quickly. Runs for a couple or three minutes then starts to miss fire and back fire . Sounded like possibly bad plug or so. Anyway haven't had a chance to go over and look but kinda curious if it could be bad gas and now much more serious. Any suggestions or procedures recommended greatly appreciated.

Thanks

In my case with the bad gas it took awhile before it caused valve issues in my mower. I highly doubt bad fuel could mess up valves on your buddy's big block as quickly as 2-3 minutes.

My knee jerk reaction is backfiring sounds like a timing issue or an issue with the valve train not operating properly. Bottom line is I would go back to basics and check everything carefully. Check timing. Pull valve covers and make sure the valves look like they move properly. Pull and check the plugs. Check firing order, etc.

Good luck