Comment by taejo
2 years ago
Plenty of cars that intermittently won't turn on in this thread, but I once had a car that intermittently wouldn't turn off... or at least the headlights wouldn't. I assume a relay somewhere was overheating and that was making it stay closed, but I never debugged it, and nor could my cousin who was an auto mechanic. We never tried too hard, though: I would just take the fuse out if it happened and put it back the next morning.
True story: I had that happen to an airplane. I was a student on a long solo flight and on the last two legs of that flight, the engine wouldn't shut off using the usual method of pulling the throttle back to idle and turning off the magneto.
It's been long enough that I don't remember what I did to get it shut off (maybe I toggled a circuit breaker?), but when I got back to base, I made a note in the airplane log about the problem and also left a note for my instructor, who was out that day.
When I came in for my next lesson, instructor mentioned that the next person to use the airplane, also a student on a solo cross-country, got stranded 100 miles away because when the engine wouldn't shut off, he panicked and pulled the throttle hard enough to rip the cable through the firewall. Airplane had to be put on a flatbed to get it back home.
Guess he didn't see my note!
Sounds like it might have been dieseling - enough carbon buildup glowing hot that even with both magnetos off it can still ignite the next rotation.
Usually there was a fuel disconnect along with the throttle that would eventually starve the engine.
That's probably what I did. Thinking back, the first time it happened, it just took about 10-15 seconds to shut off. The next time, when I was back at my home airport, it wouldn't stop running at all and I think I turned the fuel cutoff to get it to stop.
The radiator fan in my Jeep did that in Sudan when it was 48C. Better to have it stuck on that stuck off in those temps!
I just tapped the relay with a wrench and it un-stuck and turned off.
Funny enough that was almost 5 years ago, and it hasn't done it once since in more than 80,000 miles of driving. Not in -35C, not in +45C. Odd little relay.