I once had a riding mower that developed a thirst for oil. I don’t mean just a little smoke here and there. I mean massive clouds of smoke until it warmed up and then it would flash over and burn the oil as flames out the exhaust. It got to the point where it was going through about a quart every 10 minutes. Then there was the fact that I would turn the engine off and it would still be running on the oil like a runaway diesel.
I had several people offer up their reasons why this was happening and the one that made the most sense to me was blown head gaskets. This would offer a nice supply of oil and extra air from the crankcase to make it run extra lean and hot to where it could do this. Others kept suggesting the timing was too far advanced but the flywheel key seemed fine and replacing it made no difference. Anyone have other ideas?
I have videos that I will have to dig up from this as filming at night was quite spectacular.
Anyone ever seen a gasoline engine runaway on oil? If it was hot enough you could mow the yard with the key in the off position. The only way to get it to shut down was to choke it and even that didn’t work some of the time. It would slow down and the flames would transition from blue/white to yellow/orange so wasn’t as hot but would still run like this.
This was a Kohler Courage that had given me fits with other small issues so when it started doing this I really didn’t care to look into fixing it.
Sounds exciting. Never had or seen anything like that. I’ve had a couple oil burners but they would just foul the plug, never run on their own. If you’ve still got it, crank it up and fog your yard, the mosquito crop has been terrible the last couple of weeks. I drove out to the cemetery to pull the flags and those little critters were just swarming around the car before I even got out.
In order for combustion to occur, hydrocarbon molecules have to be in direct contact with oxygen when the heat energy is added. Gasoline is highly aeromatic; it vaporizes into the air, surrounding itself with oxygen, so it burns readily. Oil is not. It does not vaporize at ambient temperatures, so it doesn’t surround itself with oxygen and burn. It will vaporize if heated enough, and then will burn, but not at ambient temperatures.
In fact, the burning you see gasoline doing is actually of the hydrocarbon molecules that have vaporized into the air. The liquid itself isn’t burning.
My ex-girlfriend had an old 1980s Camaro that caught fire due to oil leaking onto a hot exhaust pipe. I’ve heard the same can happen to Hondas that have the oil filter on the back of the engine right over the exhaust pipe, especially if the old oil filter gasket gets stuck behind when you remove the used oil filter.
It can vaporize and burn (and stink like crazy) if it drips onto a hot enough exhaust manifold. But it needs to get hot enough to vaporize, and the exhaust system (especially the cat converter) are the only things that might get that hot. I’ve seen an exhaust manifold on an engine with a problem (lean operation) get hot enough to glow… but that is well above normal manifold temps.
The engine is toast. It finally got to the point where it would foul a new plug in like no time and had no power to mow. Yes, it took like 5 minutes to get hot enough to where it would run on its own oil and blow fire instead of smoke. There wasn’t gas in the oil but the level was dropping rapidly.
Besides this problem, the charging system now longer worked and I had countless other issues with the engine so one day I got a little lazy about adding oil and it just locked up hard. I talked to a mower repair shop and he had seen many of my engines give it up for various reasons and suggested just running with it until it quit so that is what I did. As I said, it had so little power by the end that it was pointless to keep around. The Kohler Courage wasn’t designed to last and give many years of good service. The good news was that when you got into tall grass, you could always burn it down with this mower. Seriously, I got into the habit of always having a fire line around any tall grass because of this. There was actually a pretty major fire with this mower once. The mower caught fire as I was riding it down my driveway from a neighbor. The leaking oil seals and grass clippings caught fire under and around the engine. I noticed it when I started to feel hotness on my legs and then saw flames when I looked down. I thought about stopping but was like 1/4 mile from any means of putting out the fire so figured I had nothing to lose by trying to get it back to where I could put it out. The gas tank was behind the seat and away from the fire so figured that was good unless the fire spread so I just put my legs up on the dash and kept going. I knew that if it quit running, the entire thing would be done for.
So, I drove a flaming mower back about 1/4 mile and put it out. I turned it off but it continued to run like a runaway diesel on its own oil for like 10 minutes while I was getting the fire out. Once the fire was out, I then had to cool it off with water to get it to turn off. You could close the choke and it would still run like this so I suspect that there was some air leak such as with a head gasket. This would explain how an oil mist could get into the engine and keep it running like that.
That seems like a pretty cool special effect for the movies. Maybe you can get a contract for your lawn mower in the next James Bond film? … lol … I have no idea what’s causing that behavior, but I had a Lawn Boy rotory (push type) mower, two stroke I think, and one day it had no compression. When I took it apart to inspect the rings, they were so worn out and thin they were more like that really thin kind of pasta, angle hair is it called? When I tried to pry them off the piston, they broke into 20 tiny pieces. So your oil-burner problem might have been just worn piston rings I guess.
I suspect everything was shot near the end but I had always changed the oil with synthetic and this seemed to be a sudden change one day. I would consider a broken piston ring or skirt as a possibility but I doubt that the rings wore this fast to cause the issue. I guess that this would also allow more air as well as oil into the cylinder to burn.
The head gasket theory is the one I think sounds most reasonable. It would allow the crankcase to be pressurized with exhaust to help this along and allow oil to be sucked in or pushed through the breather as well. I am guessing all the oil burning allowed deposits to form rather quickly which may have remained hot and acted as glow plugs to allow the thing to keep running without spark, usually at runaway speeds.
The Kohler Courage is the consumer grade unit while the Command is a commercial line. I have a couple Commands on some smaller mowers and they are excellent engines. I would never touch a Courage again after this one. It was one small thing after another and when this happened, I let nature take its course.
The leak was mainly internal although the oil seals were leaking at the end as well. Remember that the engine was actually running on oil like a diesel so much of the combustion was taking place inside the engine and what didn’t burn came out the exhaust as nice flames. It was pretty blue/white when it started doing this but as more and more oil started flooding the cylinders, the temp dropped and it got more yellow-orange. There are a couple videos where it was blue and then changed colors a couple times.