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Can 18 months of non use of lawn mower cause a blown head gasket? Answered

I just purchased a small lawnmower at a garage sale and the owner said he had not used it for 18 months or longer. I put fresh gas in it...changed the oil and spark plug and it started right up. After about 5 strips of cutting with no problems...it started blowing out smoke and the exhaust got very hot. Is that a blown head gasket and could the sitting idle for 18 months cause the gasket to deteriate? 


Sounds like you may need to do a leakdown test on the unit. That should tell you where the air is getting past. Rings, you'll hear it through the oil dip stick tube. Valves, you'll hear it coming out the carb or the muffler. Head gasket, you'll maybe hear it from around the cylinder head or you could use soapy water and wait to see bubbles.

One product we always used was seafoam deep creep or klean-flo combustion chamber cleaner to help clean out the intake and combustion chamber

Make sure you did not over fill the oil

Oil can get into the combustion chamber and get burned if it goes past the rings, through the breather, or by getting past the intake valve seal

How can you hear the rings and the valves if the engine is running? The smoke is mostly white colored coming out of the exhaust. I checked the oil level before I started cutting. From all of the comments I have received on this site (which is greatly appreciated and I thank you very much)... I think the problem resulted from the mower sitting idle for over 18 months and the rings or seals become brittle or cracked. Does this make sense to you?

sorry it's taken so long to reply. A leakdown test is done with the engine not running and the pistion at top dead ceneter. I'm guessing it has to be oil that you are burning since there is no coolant and it's not puffing black. Unless your mower is getting covered in oil on the top of the engine or underneath, I doubt it's the seals or you would see oil leaking (unless it was the intake valve seal, if you have one, in which case it could suck oil in to the intake tract). The rings could have possibly got hung up with rust, but would usually loosen up once running for a while. Why do you think the "exhaust got very hot"?. Sometimes compression changes in a motor when you compare a cold compression test vs testing the motor when it's hot. Maybe it's just worn and smokes when hot.

You don't have the engine running ! You turn it over by hand.

Usually these small motors have some type of thin soft metal to seal the head like aluminium and just sitting idle doesnt put any strain on them.

My first choice would be gummed up piston rings, mainly the oil control ring. You could try some auto product like gumout or engine flush to clear the rings, failing that you'll have to pull the head to clean the rings and in the process you can check the head gasket.

I cut about 4 strips of grass and smoke started coming out of the exhaust and the exhaust was very hot! The mower didn't stop running so it never started losing compression which seemed strange to me. I love tinkering around motors somewhat but am an amatuer at best. Never pulled a head. You think I should try that gumout or go ahead and take it to a repair shop? I really appreciate your help.

Try the cheaper options first ie the gumout/flush, run it a while and then take it in if it still has a problem.

sounds like an oil ring has broken. When an oil ring breaks that lets oil get into the combustion chamber and will burn black smoke.

The smoke is more white than black... there was a little black but the more I ran it..the worse it got but the engine did not lose power. I am going to take it in to a shop in the morning and let him look at it.

engines will puff black smoke when the air/fuel mixture is to rich (like if the choke was left on) blueish smoke means its burning oil and white smoke will mean it's burning antifreeze ( obviously not going to be that in this situation)


4 years ago

What kind of gas did you put in it? I knew someone who put an oil and gas mix gas into an engine and it smoked like crazy. They are intentioned to use regular gas, not a mix. Also some don't tolerate alcohol mixed fuels very well.

By the way, if it was a head gasket the smoke would be coming out of the seal between the head and the block. If it is coming out of the exhaust then its from the cylinder and could could be from leaking rings.

The rototiller I fixed had not been run in over 8 years. The engine runs great. Some of the other seals have problems but not the engine.


It's just regular gas. I keep my gas mixture for my chain saw in a separate container. Smoke was only coming out of the exhaust. The mower is running just fine...lots of power but the smoke started suddenly after cutting for about 10 minutes... I bet is the cylinder leaking rings. Hope that can be fixed without too much cost. Retired on a fixed income is hard these days. Thanks for your help

Do you know how old the mower is?

18 months without oil could allow an older gasket to dry out and crack. Gaskets don't last forever.

Not certain how old...maybe 4 or 5 years. Does it cost much to get that repaired? Thanks for you reply

Does the thing still run? Did you try to finish cutting your yard?

The exhaust is suppose to get hot. Thinking about it now there is a good chance the mower is just burning off old gummed up oil and may clear up after you run it for a while. Don't think you need to do anything else with it unless it just won't stop smoking till all the oil is gown. So check the oil level, finish your yard then see if the oil level dropped at all.