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Oil pressure dropping to 0 at idle on XJ

ScienceguyXJ

ScienceguyXJ

NAXJA Forum User
Location
Colorado Springs CO
Just got my '01 XJ and when I pull up to red lights and the engine idles, oil pressure drops to 0 and the check engine light comes on. Give it some gas and it come right back up. Thought it was the oil pressure sensor but that didn't solve the problem. Maybe they put the wrong grade of oil in it??? It doesn't do it while the oil is cold. The oil is at 45-50 psi idling after starting it and the engine is cold, then it runs at about 40 through the engine warm up at anywhere from 1500-3000 rpms, nearing full temp it falls to 20-30 at idle, at full temp it's at 25-40 from 1500-3k rpms and at idle it will fall to 0. The engine is not making any noise when the pressure drops to 0 on the gauge. Nor is it making any weird noise at any other time. I'm thinking it has to be the oil pump.

Any thoughts anyone? Thanks!
 
First off, if you are running a Fram oil filter, change it. I've seen too many engines with this problem due to failed Fram filters.
 
It came with a Napa oil filter that looks pretty new, the oil looks pretty clean too. They prob changed both right before they sold it. Regardless I'm throwing on a Mobil 1 oil filter and Mobil 1 syn.
 
Not sure what grade it is since I just bought it... Kinda thinking they may have thrown the wrong grade in too but oils now a day are supposed to be multiple weight so it's not that big of a deal anymore supposedly...
 
Think I'm just gonna bight the bullet and replace the oil pump.
 
^^^ Me too, I'd try heavier oil, maybe 10-40 before I swapped in an oil pump.
 
"Forget it. good luck." Why do you say that hubs97xj? Hmmm I just don't want to replace the oil and then have to drain it and again if I have to replace the oil pump. But doing the oil is easy enough so maybe that's the right way to go...
 
You may well have a pressure/pump issue, but, you might not. I had a weird pressure issue on the highway- it would fall off to about 20, from 40-50 psi. At warm idle, it would drop below 10. I fixed mine by dumping the qwik-lube filter/fluids in favor of Mobil1 filter/high mileage oil. So, before I even thought about dropping the pan, and changing the pump, I'd throw a new filter and fluids in. The filter may look new, but if you've just bought the thing, they may have steam cleaned it or such- clean does not mean new. New doesn't necessarily mean good, either, but Wix is a trusted name around here. The fluids, though... hard to say.

edit- Don't know if anyone else does this, but it's something my dad hammered in to me from childhood- when you buy a tractor/truck/bike/boat/car, the first thing you do is change all the fluids. People lie when there's money involved. Annoying as all get out after 30 years, but I think it's good advice.
 
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For analytical reasons i think you should try 1 thing at a time:

ex 1: you change the oil, no change. Then you also change the filter and now every thing works fine: OK it was the filter.

ex 2: you change oil+ filter+ oilpump: now, you suddently dont have oilpressure at all.... ??? Now what was the reason: oil or filter or oilpump ?

See my point ?
 
TEST. Why not find out what pressure you're really at? Especially before you buy parts and perform repairs.

Get a hold of a mechanical oil pressure gauge. Many big box parts stores rent these for a few bucks. Hook it up where the sending unit currently resides.

Good data = good decisions.

If you truly were at zero psi oil pressure at idle, you should hear some noise.
 
Yeah that's what someone else suggested, hooking up a mechanical gauge to the sending unit to try and confirm the 0 psi reading. Where is the sending unit at??? I'm going to try the oil and filter tonight. Believe me, I'm going to go through and change all the fluids! Not hearing any noise when it drops to 0...
 
Are you talking about where the oil pressure sensor threads in by the filter?
 
yes, unthread the sensor and hook the gauge up there

FYI, I was getting 0 psi @ hot idle on a 4.0 that I got for free, running 10W30. Switched to 10W40 and bumped it up to about 7-8. I'm now running 20W50 and it's staying around 12-15......40-45 @ 2500 rpm. I know it needs bearings, but I'm planning to swap it out in the not-so-distant future, so I keep running the heavy stuff in it with no issues.

Jeff
 
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