White Smoke From My Engine
Easy Lawnmower Repair
"Clouds of white smoke."
This is one of the common complaints we see at the small engine shop in the Spring. The complaint is usually the same, "I put the Tractor/mower/tiller/snowthrower up for the season and it was fine all of last year. This year I take it out and I start it up and after a couple of minutes it starts blowing white smoke very heavily. Are my rings shot?"
Generally billowing clouds of white smoke are from one of two things. Either the crankcase breather has failed or the oil is contaminated.
The crankcase breather vents the gases and excess pressure from the crankcase and sends them through the carburetor to be burnt in the combustion process. Some breathers are nothing more than a reed valve that opens and closes as the pressure changes inside the crankcase from the piston's movement. If this reed breaks, bends or otherwise fails, then excess oil is pulled into the carburetor and the result is a lot of smoke. Other breathers are screen or filter type and when they become too fouled or broken down to function, same result, lots of smoke.
Diagnosis is done by looking for two things, oil in the air cleaner/carburetor and black oil soaked or heavily carboned spark plugs. Since oil is being fed directly into the cylinder, the plug will foul very quickly and probably also affect engine performance. Breathers can fail at any time, often they will fail over the winter as the oil that's built up on and around them solidifies and just generally plugs things up.
Repair is a pretty simple matter on many engines, just replace the breather. You can try turning the reed around on the reed type breathers, but personally I just replace them. Sometimes all they need is a cleaning though, so give that a try. Most breathers will run from just a couple dollars for reeds to maybe twenty dollars although a few that are incorporated into the valve cover may be upwards of thirty dollars.
To replace a breather, follow the tube or hose from the back of the carburetor or air filter assembly to where the breather is mounted on the crankcase. Most are simply attached with two screws but may be under the flywheel requiring flywheel removal. If it's incorporated into the valve cover, just replace the valve cover. Some are cartridges that plug into the valve cover, very easy to replace.
The other common cause for heavy white smoke, especially in mid-size Briggs and Stratton and Kohler engines, (12-20hp) is from contaminated oil. The most common contaminant will be gasoline that has leaked from the carburetor. We have had at least one engine that had a crankcase full of water, this was probably a case of sabotage from an irate neighbor.
The diagnosis is simply to examine the oil. It should have little to no smell of gasoline and should not be overly thin or muddy brown, gray, white or chunky like spoiled milk. Do not under any circumstance attempt to start an engine with oil that fits any of these criteria. The most common cause of mid-size Briggs and Kohler engine catastrophic failure we see in the shop is from gasoline diluted oil causing the rod to overheat and break just above the crank journal.
Gas will get into the crankcase when you have a carburetor that is leaking past the needle. This leak is generally caused by either a float problem or other problem keeping the needle and seat from sealing. If there is gas in the crankcase, then the recourse is a carburetor rebuild or replacement followed by an oil change. The reason that this is such a common Spring problem is that if you leave any gas in the carburetor, it will evaporate and leave behind a varnish coating that can prevent the float assembly from functioning. Also, and even more common, the ethanol in today's fuels will ruin needles and seats, preventing them from sealing the flow of fuel off, which causes the carburetor to overflow and leak into the crankcase. Gas can also get into the crankcase from a fuel pump that's leaking, so if you have a pump, that needs to be checked as well.
These items are often the result of improper storage. I can't stress enough the importance of proper storage of outdoor power equipment.
If there is water in the oil, then several crankcase flushes with kerosene and a few oil changes may clean the engine out. However engine disassembly may also be called for to remove all the muddy deposits and ensure that the oil channels are cleaned out.
These two items are the most common causes of a lot of white smoke. We do see a few OHV engines come in and have blown head gaskets. Usually this is on a Kohler and often the oil is leaking down onto the exhaust manifold and not into the cylinder. A leaking valve cover gasket will also do this.
If the plug isn't fouled out, and the oil is normal, then check closely for a leak. Spray carburetor cleaner on the head to clean all deposits off and then run the engine for a bit. Then check for a leak again. Some talcum powder thrown onto the surface will help to spot a leak as well.
Hopefully one of these will be the solution and you won't be purchasing a new engine. If you need further help, think about posting your question on JustAnswer.com in the Small Engine category. Good Luck!
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.