1981 J10 4.2L AMC - high temp and oil pressure


New member

I spent most of the summer getting my dads old J10 running. I swapped almost all the fluids and replaced some parts like fuel filter, thermostat etc.. I am in Alberta and have driven it with no issue since the summer until recently.

I was driving home and I noticed that my oil pressure started to spike and at the same time the engine temp started increasing too. The oil pressure reached the high mark within about 30 seconds and the temp was right behind it. I stopped, checked fluid levels, and proceeded very slowly. The issue resolved about 10 mins later but it came back the next day. I got an oil change with a flush and the issue went away for about a month but it just came back.

Does anyone have some clues as to what could cause this? I flushed the coolant and put in a high temp thermostat in August and it worked fine all fall. The engine would heat up and the temp would sit at the low end of the temp scale wether it was +30c or -30c. The attached pic shows what the gauges looked like the last time it happened.

Thanks in advance!


  • A0942D33-BEC3-4B53-BA3A-618AA910F938.jpeg
    640.9 KB · Views: 45

The connections are good on the back of the gages?

I would check the grounds on the engine and maybe add an extra. Other wise, find where the little spring and ball is that controls the oil pressure and pull that stuff and make sure there is no junk in the passage way.

Looks like there is one in the pump assembly and a bypass at the oil filter mount area.


Thank you very much superj! I will check that out and see if there’s anything stuck in there. While I have it open I’ll probably replace all the little springs etc I can and hope that works.

The part that confuses me is the high temperature. I can’t make sense of higher oil pressure increasing engine temp. Could it be the other way around? I’ll have to take the dash apart and check out those connections and add a ground as you mentioned.

I don’t have a copy of those schematics. Any chance you have one showing where the engine temp sensor is?

Thank you very much!
i found that stuff on google and i have forgotten where they were on my old 4.2

the temp gage is what makes me think its a ground issue

Sorry for the delayed response but you were 100% correct when you said it was a ground issue. I checked the negative lead on the battery and it was cracked where it clamped on. Replaced that and it fixed the issue. No more wandering gauges.