Anyone have knowledge on these small devices used to shut down small gas engines on low oil condition? I've one here that appeared to be defective off a Coleman Powermate generator. I used one off an unknown engine and it works so these devices must be fairly universal. Attempting to reverse engineer these things. I've pulled it apart to trace the circuit. The lead from the coil has voltage when running supplied from the coil and magnets on the flywheel and the lead to the oil switch is grounded on low oil. What I think happens is the circuit "seals in" or latches the moment a ground is provided from the oil switch. After the engine stops the circuit discharges and you're ready to start up again. This is what was happening with my generator. It would run for about 30 seconds and quit until I disconnected the oil sensing circuit. Here's a sketch of what I found. I hope it's accurate. I could not determine what the transistor like device is.

TIA

 

It could be that the oil level was right at the point of bein low and when the engine was running, oil was splashed around inside, lowering the level at the sensor. Once shut down, the oil was allowed to drain back to the sump and closing the low oil switch. When started, the oil moved out of the sump and spread itself all over the inside of the engine allowing the sensor to show low level shutting it down, and the cycle would repeat. Just a guess on my part.

 

I thought of that but the oil level wasn't what I considered too low. It was still about half way up the dipstick. What I should have done to eliminate that possiblity was top it to the max. Little late for that now but I could replicate this by dropping the oil to the same level using this good module. Actually I think I'll do just that in a couple days. Be away till Sunday night.

 

The theory of low oil is correct......the splash system can keep enough oil topside to cause the sensor to do a nuisance trip.
I ran across this a lot working for good ol' J. Deere, as some fancier mowers and tractors would trip the low oil if you were mowing in line on a grade, as opposed to up-down.
Many machines without low oil detection, would detonate on a grade, if the level dropped below the sump and starved the crankshaft, especially if the oil was already beat to death.

 

On my zero-turn mower with a Kawasaki engine (pressure lube), if I hit a big bump, the engine will stall for a split second due to the float in the sump bouncing. On cheaper engines with splash lube, I have never seen this happen, but they can start and then shut down for the reason previously explained. In addition, the float can sometimes stick to the bottom of the sump, and the engine won't start regardless of being full of oil.