Anyone ever had a gas engine run away on oil like a diesel?


#1

I once had a riding mower that developed quite the thirst for oil. I just dealt with it for a while and added oil as needed until it started running on its own oil like a diesel in runaway condition. I could turn the key off and it would run without spark until it didn’t fire at the ideal time and would then sputter and bounce to a stop. It would usually be so hot at this time that flames would be coming out the exhaust and the muffler was glowing red hot. Has anyone else ever seen this happen with a car engine? I would expect that something like this in a modern fuel injected engine would be quite hard and that it would be easier in an older carbureted engine.

I was just thinking back on this and wondered if anyone had seen anything similar with a car engine. I mean it would drive and mow like this if it was really heated up. I found that out thinking that turning the key off with the deck and transmission engaged would kill it. Sometimes that worked but sometimes it just kept running.


#2

yes, old carburetor engine in my 1966 car did that for few seconds after turning off, due to substantial carbon buildup on pistons

after I’ve got engine block machined to next extended piston/rings size and had everything reassembled properly, it stopped both eating oil and “dieseling” :slight_smile:


#3

I believe it was running on gasoline, but “dieseling” because of hot spots in the cylinder head. Oil does not have the vapor pressure such that a gas engine could run on it.


#4

It had been burning oil for a while so I wondered if maybe deposits formed that either formed hot spots or enough volume of the combustion chamber was taken up to effectively increase the compression.

It would smoke like mad when first started. Once warmed up a bit it would start blowing fire out the exhaust. It wasn’t nearly as bad if the thing was under load and mowing but would run away more often and blow fire when the deck wasn’t engaged and the engine was unloaded.

There may have been gas mixed in with the oil to help with this process but it was DEFINITELY burning oil. Towards the end I had to add more oil than gas to this thing. This thing had given me so many problems that I didn’t really care to repair it. I just kept it running into it locked up and quit one day. I was pouring drain oil from my vehicles in it once it got that bad.

Here is a video of it when first started. https://www.youtube.com/watch?v=IkjtBMGPit8 You would start it and stand back for a few minutes while it warmed up.

You would start to get the fire once it was warmed up. There was very little smoke in comparison to when it was started from cold so think the oil was actually burning in this case. I still had to add lots of oil so it was going somewhere. https://www.youtube.com/watch?v=rVQefzo-Qx4

It did start leaking towards the end but think most of it was burning and I mean flames and not smoke. I was so fed up that I wasn’t upset when it finally quit.


#5

I would agree that the engine was running on gasoline and not oil. The reason for this is that the.piston top was covered with carbon and the carbon when hot would fire the next charge of gasoline when the intake valve opened. The engine ran way out of time which explains the red hot muffler
In an old Popular Science magazine from the .1950s, there was a monthly feature called “Tales From the Model Garage” with its proprietor Gus Wilson. In one episode, Gus helped an army friend win a contest with a Jeep. The point of the contest was to waterproof the ignition so that the vehicle would run under water as long as possible with stacks for exhaust and combustion air extending above the water line. Gus prepared the Jeep by drilling holes in the exhaust valves. These holes quickly built up carbon deposits and the engine ran with out an electric ignition system.


#6

It sounds very similar to the dieseling that auto manufacturers suffered with in the early-mid '70s when they began to run hotter plugs and leaner mixtures to try to reduce emissions. As long as there was still gas in the float bowl, the vacuum from the intake strokes would pull it into the cylinders and there was enough residual heat in the engine to initiate combustion. The problem was solved by adding an “idle stop solenoid” to the accelerator linkage. The idle adjust screw was on the solenoid, and when the solenoid was deenergized by turning the key to OFF the throttle plate would totally close, cutting off all air and choking the engine.

I was not uncommon back then, before they introduced the solenoids, to walk past a new car in a parking lot and hear the engine chugging away.


#7

The difference between gasoline and diesel engines is that with a gasoline engine you control the intake air valve, a gasoline engine cannot “run away” like a diesel when the throttle valve is closed.

To run-on at idle with a hot engine is a different experience, a hot carbureted engine can run on if the idle speed is too high but will not “run away” to destruction as with a diesel engine.


#8

Regarding the mower and engine type, there was likely an air leak around a breather tube or fault with the breather valve.

Some years ago I remember a gas engine that was trying to run away but it’s been so long that I can’t remember the engine type. It would sit there and start idling faster, and faster, and take off. It was an F.I. car is all I remember.


#9

I really enjoyed Model Garage. Learned a lot from the stories.


#10

Deiseling was not uncommon on cars with carburators. Had a 1970 350 Cutlass
To prevent deiseling I would put it in reverse then turn the key off. A cross country trip must have taken care of the carbon build up. No deiseling after trip.


#11

You beat me to the “idle stop solenoid”. cwatkin can turn off the mower gasoline engine the same way diesel engines are stopped by shutting off the fuel supply. Perhaps an inline valve in the fuel supply line that could be opened to start and run then closed to stop.


#12

I saw an article that Mazda was experimenting with an engine that ran on gasoline but used compression ignition like a diesel, by using very carefully controlled injection of fuel directly to the combustion chamber. They were trying to get the efficiency of diesel without the particulate emissions of diesel fuel.

Having an engine run on its oil seems unlikely because any engine that consumed oil like the OP says his did would not be likely to have the compression needed to function like that. I suppose if the top rings were OK but the oil control ring was completely seized with gunk it might happen.


#13

the engine was a Kohler Courage. My opinion is that these are better used as boat anchors than an actual engine. It was nothing but trouble for me. About anything and everything that could go wrong with it did. I had another one and it at least didn’t linger like this one. It just blew one day. I have a few Kohler Commands (commercial line) that I run as hard as they will run and they just keep coming back for more. I change the oil once per year and that is it. The Courage is the cheaper consumer line and it is junk. Spend the extra bucks for a commercial engine.

I think the comment about an air leak was right on. I always had the feeling this engine was pulling air from somewhere it it would run away even when throttled down. I think the air leak as well as the oil leak was internal. I have always wondered about a blown head gasket between the pushrod gallery and the cylinder. I made sure all mounting bolts on the various flanges were tight and visually inspected everything. I even tried the carb cleaner/starting fluid trick around likely leaks and never found a thing. I wonder if it was coming through the engine seals. These were leaking quite noticeably towards the end of this thing. Oil would pour down from under the flywheel and run down the sides of the engine. Maybe it was sucking air into the crankcase through an engine seal?

The Commands were also known for cracking the block under the flywheel but more so on the single cylinders. This was a twin but anything is possible.

Then one day it had a fire. The thing was running so hot that this didn’t surprise me. All that oil and the crud that stuck to it just flashed over one day and caught fire. I almost abandoned the mower where it sat but figured I would take my chances and drive it the 1/4 mile or so back to the house. I sprayed it with the hose from a distance which I know is the best with an oil fire but I put it out. The thing continued to run and scream in runaway condition for several minutes until I got it cooled down enough with the water that it turned off. All the ignition wiring was burned through so it was definitely running without a spark. I repaired the wiring harness and went on with life.

It was definitely burning oil. How else would you account for the oil consumption and smoke? It wasn’t leaking much oil until near the end. The smoke was horrid until warmed up, then it would flash over to flames. It may not have been burning pure oil and had help from the gas that was mixed in but think the oil was burning. I literally was stopping every 10 minutes to add oil by the end.

The only thing restricting the speed of the engine was the amount of oil it was burning. Basically, could tell that at higher RPMs it was pumping more oil into the cylinder and it would start to bog down and smoke because it simply couldn’t handle that much oil. Here is another video kind showing this self-limiting behavior.
https://www.youtube.com/watch?v=h0JenRQvFkQ Basically it would run this way RIGHT before it flashed over and went to flaming out the exhaust.

The stop solenoid was another issue with this thing. It seemed to work most of the time but when it didn’t, it would always fail closed while I was mowing. Then there were the backfires this thing was meant to prevent. They sounded like an explosion and eventually blew the muffler to pieces while I was mowing and mowed over them. I shut the mower off at a neighbor’s once and they said the mower must have exploded. I told them this would just happen and that it was nothing that odd for that engine.

I had a chainsaw run away to destruction once. A tree had fallen on it several months prior. It was a Stihl so I rebuilt it from parts off a junk saw that I had laying around. It never ran quite right after this and would guess it had an air leak. It would be very temperamental in that you couldn’t keep the fuel/air mix straight. It would lean out and start to run away so I would enrich the mix. Then it would choke down and start smoking as if run too rich, then I would lean the mix. It was always this way after the tree fell on the saw. Anyway, I was cutting a pretty large branch one day and the saw started running away after I unloaded and throttled it down. I just kept on screaming. There was no choking it down. It just kept on screaming in runaway condition. I just held onto it and kept it away from anything I didn’t want harmed as it ran away. Then it finally started to slow down as molten pieces of the engine were emitted from the exhaust. It then locked up tight as a drum! I knew it was trash after the tree fell on it so any extra use was a bonus.


#14

In the old days Kohler and Wisconsin were quality engines but they all have their different grades now so one is not better than the other unless you get more of a commercial grade, like the Briggs Vanguard I think. Even the Briggs IC (Industrial/Commercial) is more of a consumer grade even though I’m pushing 600 hours on mine with good compression and no oil use. Regular oil changes.

I’m trying to remember though but years ago I had one smoking pretty bad that I think was the breather. I ended up just replacing the junk engine though so never really resolved it.

But Taryl fixes all


#15

It isn’t worth fixing this junk these days. Off to the scrapyard it goes!

I have had a few Briggs consumer engines run great until the moment they grenade. I have had a couple eat the valves, destroying the head and putting a hole in the piston. Then the counterweight assembly broke loose on another one. It was idling slowing and can only imagine the damage it would have done had the thing been running at a normal speed. Either way, these things are not worth fixing. I actually dissected that one and was shocked that the bracket holding the counterweight was thin cast aluminum.

I would rather find a used commercial engine needing some work than mess with a consumer grade.


#16

After I’ve got 2013 Mazda3 with “skyactiv” engine for my wife, I’ve discovered they raised compression ration to 12:1 or so, but it still runs nicely on regular gas, then I’ve read that new skyactiv generation will raise compression even further and will get rid of spark plugs, going away with diesel-like compression ignition


#17

Here’s how the Skyactiv-X engine works (still uses spark plugs to trigger the combustion):


#18

It will be really neat of Mazda can perfect this engine. I have read about it and figure I wouldn’t want to be one of the first adopters but that it will be great if it works out.

Or, you could just have a crappy Kohler Courage mower engine that continues to run with flames shooting out the exhaust without any sort of ignition. I am sure the Mazda design is way more efficient though!


#19

My fiancee’s old 1980s era Camaro did that, but I’ve never had it happen on a modern fuel-injected engine.

BTW, I don’t think it was running on oil, it was “dieseling.” Here is an informative YouTube video about it:

Dieseling - How to clean out your carburetor


#20

I figured it would be hard for something like this to occur in a modern fuel injected engine. That being said, I guess anything is possible with an air leak and leaky injector! I know a guy who had a 1996 or so Mitsubishi Eclipse. Somehow he did some work under the hood and caused an air leak so it idled at like 2500 RPM. He never bothered to fix it and just sold the car as is to someone.

Did the Camaro run away or sputter and chug after being turned off? I know a lot of older cars would chug along. Here is a good example of this.

You really get the chugging in the second one before the big boom! This car definitely smoked like my old Kohler engine.