I hate being the one to beat a dead horse but I'm at a loss. After last oil change, pressure kept skyrocketing up to 80 psi when cruising and would drop back to 40 at idle. This happened after the engine was just staring to get warm. On top of that, there was a small leak coming from the filter area (I think, ha) but nothing to be alarmed about. Just old Butch marking his territory.

After a while it started doing the opposite. Good pressure when cold, then dropping to 10 psi at idle after engine warmed up. I've got one guy telling me it's fine, nothing to worry about. Another guy says oil pump. And another guy says cam shaft bearings! So where do I start first?

Napa filter on last oil change. Just did another change a few hours ago and slapped a Mopar filter in it with 5w-30 conventional. New sending unit about a year and a half ago. 97 4.0L with 135k on the clock and still runs like new. Suggestions?

 

Odds are that your oil-pressure sending unit is bad/going bad (the pegging at 80 psi is usually a dead give away of this). 10 psi isn't really below spec. anyway , factory spec. is 13 psi at hot idle and the gauge isn't particularly accurate so 10 psi is close enough but it is likely that your pressure isn't really that low and it is just a faulty sending unit giving a bad reading. They are a common failure item and are really easy to replace (it is right above the oil-filter).

 

They're also easy to break if your filter wrench slips! Lol.

 

^^This^^
It doesn't take much to damage the sending unit.

 

You might try removing the wiring harness connector from the sending unit and spraying contact cleaner on both sides and see if the problem continues before buying new parts.

 

Put a new sending unit in and made sure to clean the contacts on both the plug and the sender. It's a little better (sitting around 13 psi) but it's not what it was when I first got it. It used to sit around twenty at idle. But since 13 is the minimum listed by Jeep, should I just call it a day?

 

I lied. After driving it some more the pressure still sucks. Next step?

 

put a mechanical gauge on it first and foremost. then report back.

 

Mechanical gauge reads the same as the dash. ~10 psi hot idle, ~40-50 when you rev the engine. Next step is...?

 

Where did you mount the mechanical gauge? What's the oil pressure at cruising speed (say 55-60)?

 

I just pulled out the sending unit and had it in there. Pressure was around 45 at that speed. The driveshaft vibrations from my 4.5" lift were about to rattle my fillings out though! Lol. Getting that fixed this week when the SYE comes.

 

Fillings aren't cheap so I'd be getting that fixed.

Did you check out the hole to see if it was clean before installing the gauge? Just wondering if something there could be affecting your reading. Mainly because of the variation you got originally.

 

I shoved a pipe cleaner in there before I put the new sender in yesterday. Nothing funky on it. Just fresh new oil.

 

Things look clean and getting oil under the oil filler cap? As someone said your in spec with those pressures but if something simple can increase it why not.

 

My thoughts exactly. And like I said when I first got it it never ever dropped below 20 psi. Just a little annoying issue I want to deal with.