oil pressure and oil concerns

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Jan 13, 2003
collierville, TN
well first i'd like to say howdy- im a noobie..

My questions stem from my jeep wrangler (97 model year) but with a rebuilt 4.0L that has about 10K miles. I ran synthetic through it for a few thousand miles but it began leaking so i swapped over to dino with no problems. My pressure seems to be low to my standards... at cold startup i get 40-42, cold driving 40-45, warm i get about 20 but the more i drive the lower my idle goes... These figures are the with the current temps ranging from 25-60. In the summer when the temps are between 80-100 with high humidity i get bout 40 on initial start, then like nothing at idle and about 20 driving. Could this be a sensor issue? This is dealing with 10w-30 oil but when swapped into 20w-50 i dont have oil pressure concerns. Should I run 20w-50 or seek other options? Ive been running the STP S8a filter and have tried other filters but havent seen a difference in pressure. For oil ive been running the mobil 1 dino 10W-30 but at next change would like to swap in the 20w-50.... good idea or not? Do rebuilt engines have looser tolerances? Is that why you shouldnt run dino in em? Thanx and sorry for the multiple questions
Yes, those senders do often go south. If it weren't a fresh rebuild I'd also suspect the pickup. Get a real (mechanical) gauge on there and confirm pressures before doing anything. Certainly, check with the rebuilder before going to a 20W50. There are a bazillion variables and 20W50 may be fine. Or not.

Higney, I also have a 4.0 Cherokee. Before you do anything else, check the connector on the oil pressure sender. Make sure it is clean and tight. I had all sorts of erratic readings on mine, because of a loose connection.

Oh yes.......
to the board.

[ January 15, 2003, 09:32 PM: Message edited by: TheLoneRanger ]
"Do rebuilt engines have looser tolerances?"

Not generally but many do not get the cam bearings replaced if the block is not vatted, vatting will ruin the bearings and force replacement". Sometimes the crank is just polished and std bearing size used,this increases clearance over factory tolerance.

Do the reciepts reflect new cam bearings and oil pump?

Anyway good oil is available where you live,,there should be some Union 76 oils and Phillips.Kendall galore to meet you needs along with other common brands if the sender or oil pump ect is not the problem and you choose to bandaid it with a higher VI oil.

Good luck.
My Grand Cherokee oil pressure would do the same thing. I had a new oil pressure sender on and it is like new. My idle is 60 psi hot at speed, 35 psi hot idle. Before the new sender it was 40 hot at speed and 15 hot idle.
Yeah my Son's old IROC's sender was working but leaking. He went to town and bought one and magically it had a pegged gauge when cold,,,with the same 10/30 oil that was 60lbs before at start with 80F ambient. They sold him the wrong sender.Or it was defective ? Too hard to remove again,the leak was stopped so he lived with it.
I hate to be the odd man out on this but... While the sender may be bad, I'd be concerned about the whole "rebuild." I don't know if the Jeep 4.0 is prone to leaks so maybe that's "normal" but the pessure sure seems low to me for a just rebuilt engine. It makes be wonder if they got all the bearing clearances correct, if they used a new oil pump, etc...
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