I've got a 1991 E150 5.0 liter with 200,000+ miles and recently, usually at
stoplights, the pressure needle will swing to the max position in about 3
sec., followed shortly by the temperature gauge going to the max. After a
nerve-wracking few seconds the oil pressure comes down, then the temp.
Research has indicated a problem with the oil pressure relief valve, the
gauges or the voltage regulator that feeds them. I would think that with a
voltage regulator problem, the needles of the gauges would move together but
there is a definite lag by the temp. gauge both going up and coming down.
There is some question about whether the water temp. gauge can realistically
change that quick (normal to max in 2-3 seconds), I don't know the answer.
I'm planning to put a mechanical gauge in but the chances of catching the
event are small as I haven't been able to reproduce it on command. After
months of just seeing the temp. gauge come down and thinking it was a sticky
thermostat, I've only recently caught the whole sequence start to finish.
Does anyone have experience with this kind of problem? I'd appreciate any
insights that would narrow this problem down.