Smoky mower :-(
July 17, 2010 11:24 AM   Subscribe

My sit on lawn mower is billowing white smoke from the exhaust.

It has been tipped on its side, with the air-filter side facing down. I've taken the air filter apart and whilst the filter was a bit greasy/oily on on side, there was no sign the whole filter had been coated in oil. The exhaust pipe had oil in it, and when I cleaned the accessible area with a rag, the mower started up fine and was venting clear fumes for about half a minute. Soon enough, though, the smoke returned and when I finger tested the exhaust pipe, the oil was back.

How can I clean the exhaust itself (I can remove the whole exhaust) if that's where the oil is residing now? IS the oil in the exhaust, do we think, or somewhere further up? I wish I knew.
posted by dance to Home & Garden (7 answers total)
Is your mower water cooled or air cooled? White smoke is usually a sign that coolant is making it's way into the combustion chamber. Bluish-white is usually oil. Also, what does the smoke smell like? In particular, does it smell oily? (burning oil has a pretty distinct smell)
posted by deadmessenger at 11:36 AM on July 17, 2010

Tipping it over probably caused oil leak down from the crankcase into the cylinders. It's not a good idea to do that, but it generally won't cause any harm. Not unless it causes too much oil to leak out and not leave enough in the crankcase. Check the oil level and make sure it's correct. If it's too high then the oil will potentially foam and that can get forced up into the cylinder.

Do a more thorough job of cleaning. "Accessible" doesn't sound thorough. Pull the air cleaner off and look down into the carburetor. Make sure it's entirely clean of oil. Use a carb cleaner spray. This has to be done with the engine running, lest you have that seem into the crankcase oil (and ruin it). Carb cleaner spray will cause the engine to stumble, so be ready to goose the throttle to keep it from stalling.

But is this a mower with an actual radiator and coolant? Or just a small-medium sized one that is just air-cooled? All but the larger ones are typically just air-cooled. If it's got coolant then white smoke often means a coolant leak and expensive repairs.
posted by wkearney99 at 12:14 PM on July 17, 2010

It's possible that oil either landed on the exhaust manifold/exhaust pipe or got into the combustion chamber.

If it laned on the exhaust manifold/pipe, then it's going to smoke for a little while, because those parts get super hot when the engine is running. It'll burn off eventually, but it'll smoke until then. Because it runs clear for a little while, and then beings to smoke, my bet is on this being the issue. I'm thinking it takes a little while for the exhaust pipe/exhaust manifold to warm up, and then it starts spewing smoke.

Ditto with oil in the combustion chamber, although I would think that it would clear out quicker than if it were on the exhaust.

How long was this thing tipped on its side?
posted by spikeleemajortomdickandharryconnickjrmints at 12:18 PM on July 17, 2010

wkearney99 got it...if it's air cooled, let it burn off the oil that seeped into the cylinders... it will be fine...
posted by HuronBob at 12:20 PM on July 17, 2010

Thanks a lot for your help!

I am pretty sure it's an air-cooled motor because I can't see a radiator or radiator cap.

I'll try and take off the engine case and look down into the engine to try to clean it of oil. Would it work to remove just the exhaust and clean that somehow? Would pictures help?

Thanks a lot!
posted by dance at 12:22 PM on July 17, 2010

Just live with the smoke for a while. It'll be your reminder not to tip it over again. Really, by the time you go through the effort to degrease everything it probably would have burnt off from engine heat. It might help to mention make/model of the mower, to be certain.
posted by wkearney99 at 1:32 PM on July 17, 2010

Are you 100% sure it's coming from the exhaust? I recently thought the same thing, but it turned out the smoke was actually a belt burning up right under the muffler. When I looked behind me while sitting on the mower I couldn't tell that the smoke was actually coming from under the mower.
posted by COD at 3:22 PM on July 17, 2010

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