I just re read this entire thread. I read the oil gauge works but have no clue how it works, what it reads.
The above post along with a couple others suggest a working but faulty mechanical limiter. It should produce a pulse voltage that can operate all 3 thermal gauges but it does put out a higher current during warm up period before leveling to the circuit demand. So maybe its' leveling to a very weak pulse voltage and that takes the path of least resistance to ground. Thus 2 or 3 volts going through the oil gauge at start up, leaving notta for the temp gauge.
There would need to be a serious fault in the oil gauge circuit for that to draw away all of a good limiters output but... maybe that is possible. I haven't seen every condition, every way a oil sender can feck up.
So just for knowing... disconnect the oil sender and isolate that wire terminal. Now lets see if the temp gauge responds differently. If it does, we know the fault is in amount of limiter output going to where? and why? to replace the oil sender wouldn't break the bank. If that yields no joy...
Next question is... Is the limiter truly bad or is it only lacking a good chassis ground? It gets its chassis ground via a small piece of metal on its back pressed against the inst housing and inst' housing screws to dash.
It is possible that all of these instrument problems are due to 3 loose mounting nuts on the fuel gauge.
I must add that if I determine the fault is inside the car, and I must pull the inst' panel and disassemble it, I will install a solid state inst' voltage regulator while I'm there.
