My 4.0 is stock with 170,000 miles on it. Recently I got a salvaged 2005 Wrangler TUPY head and had it remanufactured and put on the XJ. I had the pan pulled and the oil pump replaced at the same time.

After this partial rebuild, the cold start/run oil pressure surges up to 75-80 psi under acceleration until warmed up when it settles down to about 45 under acceleration. A HOT idle is about 18-25 psi.

Oil is 5W-30.

The cold oil pressure seems a bit high to me.

Anyone?

Thanks.

 

Have you checked the pressure with a manual gauge? Might have a bad sender or the passage is clogged causing a high reading. I had this last one happen right after an oil change.

 

I should have mentioned that I have several sending units laying around and swapped them out and get the same readings.

The readings are accurate (at least as accurate as the dash gauge can be).

So the original question: is 75-80 an expected (normal) oil pressure for a cold engine under acceleration?

Thanks.

 

I take it you didn't see 75-80 psi before the head/oil pump change (?)

There's nothing in the head itself that would cause higher than previous oil pressure, so it rests with the oil pump. Was this a high volume pump installed or a standard pump?

In any case, I wouldn't worry about the oil pressure bouncing off the oil pressure relief valve...for now.

I had an experience with my oil pressure suddenly going to 80 psi on start but come back down to 40 psi after warm-up. As time progressed I noticed that at idle the oil pressure would drift slowly from 40 psi to 80 psi then dump back to 40 psi. It progressively got worse, i.e., happened more often. Then finally the oil pressure would follow the throttle up to 80 psi and stay there. It looked like the relief valve was not working (75 psi) and that since 80 psi is the top of the indicator scale I was worried about just how high the oil pressure was actually getting.

I hooked up a direct reading gauge and it indicated the same behavior as the dash indicator, only the direct reading gauge I used went up to 100 psi., and it pegged out that gauge.

I checked with a person that rebuilds 4.0 engines and he said there's a good possibility that the front cam bearing has turned or the shell has peeled back over the oil passage holes in the bearing, causing the high oil pressure. He said he has changed many front cam bearings for this.

The engine just so happened to have piston slap so I pulled it and had it rebuilt. Oil pressure problem fixed.

So...when I said 'for now', I meant keep an eye on your oil pressure to see if you see what I saw.