Quote Originally Posted by pelago View Post
no, i beat on the original gauges from the 50's and it worked, kinda slow but it worked start up pretty high after oil and engine temp warmed up they sat at 30lbs and reacted with throttle, not like a mechanical but worked
Sometimes it takes a BFH (BIG FAT HAMMER) and then at times a LFH (little fine hammer) to make things work. Gauges are an ongoing mystery because of the variablity of repro gauges and senders.

I can only speak to my experience with the truck. The truck uses a thermal gauge for the Oil pressure. I don't know what is in the innards of the M38A1 gauge... . In the original condition, the truck sensor was another thermostat-like sensor that we managed to burn up through some as yet undefined oops. I replaced the original sensor with a modern sensor that is a variable resistor.

A. The new resistor sensor didn't match the gauge innards, it registered 15 PSI with engine OFF and 50+ PSI at idle. A series resistor cured that to my satisfaction.

B. As Pelago notes, the resistor sensor driven gauge responds much slower than it did with the original sensor or a mechanical gauge. It takes about a minute to come up to my 30 PSI set point and about a minute to go to 0 after I shut down. That is gauge heat-up and cool-down time, not actual engine oil pressure.

The M38A1 installation is a bit confusing since at some time in the M38A1 lifetime, the Army made all oil pressure gauges standard across their vehicles - 60 PSI gauges were phased out and 120 PSI gauges became standard. Did they change sensors too? The other Forums are not sure or even have conflicting information about that.

As we say about the First Rule of Jeep:

What we see is what we have. Trust nothing you read until you verify it.