As we are talking of an event that took days to happen, on a solenoid coil 
that can take up to 5 amps and in an automotive environment I wouldn't 
discount that repetitive effects of seemingly negligible effects and 
perhaps marginal components and unexpected power surges could fry a MOSFET 
that drives a relay that uses an 1N4007 as freewheeling diode.

We also know nothing about the car itself and we cannot assume that we have 
the old watch in a new car. Actually I think it is reasonable to assume 
that the situation is quite the opposite: an old car with extreme power 
transients all over it at crank up time. One of this cranks, or a failing 
alternator or dynamo regulator plus a weak (high internal resistance) 
battery can send even hundreds of volts transients through the power line, 
zap the MOSFET and then burn the coil.

On Monday, January 13, 2020 at 4:33:33 PM UTC-3, gregebert wrote:

> If the MOSFET turns off very fast, it's possible the free-wheeling diode 
> will not turn-on sufficiently fast to clamp the spike to a safe level; 
> given the currents involved in this circuit, I doubt this would happen. But 
> if this was an electric vehicle, engineers will be spending a lot of time 
> optimizing the design tradeoffs and probing around with a scope. 

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