Oil pressure loss and dipstick reading high

Clancy7007

Clancy7007

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Dec 1, 2023
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Virginia
Hello!
Driving to work and oil pressure read 0 with Check Guage light on. I have an 01 TJ Sport 4.0L Manual Trans 216,000mi.
I stopped and started it after a minute and the gauge read under 40 (it usually reads ~50). Revving the engine brought it up but it would quickly fall under 40 again. Checked the dipstick and it has oil 6-7in above full line.
Oil change done a month ago and in November - December I had to replace the water pump. Before the water pump failed it would show low oil pressure and didn't want to start.
Any ideas as to what it might be before I start tearing things apart?
 
Bunch of different thoughts:

-the high oil level could be a blown head gasket letting coolant into the oil. Drain the oil and see what it looks like. Also see what your coolant looks like.
-overfilling the oil a lot can lead to tons of windage and aeration of the oil which could affect pressure
-the oil pressure sensors on our jeeps are prone to failure
 
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SkylinesSuck said:
Bunch of different thoughts:

-the high oil level could be a blown head gasket letting coolant into the oil. Drain the oil and see what it looks like. Also see what your coolant looks like.
-overfilling the oil a lot can lead to tons of windage and aeration of the oil which could affect pressure
-the oil pressure sensors on our jeeps are prone to failure
Click to expand...

Thank you!
I've only ever put 6qt in or up to the dipstick full line for oil changes.
I'll be draining the oil.
 
Might be a good time to unplug the dash sensor and hook up a manual oil pressure gauge...you can buy a cheap one on Amazon or rent one from the auto part stores. Fitting is 1/8" npt.

Head gaskets in Jeep 4.0s are easy. The hard part on the latter year TJs is getting the exhaust apart.

-Mac
 
Pardon what may sound like a stupid question but could you have not wiped the dipstick off before reinserting it to check the oil during that stressful situation?

Most oil pressure problems are nothing more than a bad oil pressure sender. If you replace it make sure to avoid cheap store brands which don't usually last long. Many don't even work properly. The first two Duralast oil pressure senders I got from Autozone years ago didn't work properly, only the third one did. And all were the same model number of Duralast. One of the two bad senders even worked backwards... it indicated a high oil pressure at idle and dropped each time the engine was revved.
 
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Jerry Bransford said:
Pardon what may sound like a stupid question but could you have not wiped the dipstick off before reinserting it to check the oil during that stressful situation?

Most oil pressure problems are nothing more than a bad oil pressure sender. If you replace it make sure to avoid cheap store brands which don't usually last long. Many don't even work properly. The first two Duralast oil pressure senders I got from Autozone years ago didn't work properly, only the third one did. And all were the same model number of Duralast. One of the two bad senders even worked backwards... it indicated a high oil pressure at idle and dropped each time the engine was revved.
Click to expand...

I wiped and reinserted the dipstick several times because I didn't believe it. I even waited a half hour and checked again, same thing.
 
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There's really only a handful of reasons that your oil would read that high - either a) there was too much oil put in it at the time it was changed, b) you have coolant in the oil, or c) you somehow have water in the oil. You didn't indicate what the oil looked like though - in a running engine, if there is either coolant or water in the oil you're going to get that stuff whipped into a creamy brown surprise (the forbidden milkshake) and I imagine you'd have noted that in the original post. Now, if you let it sit and the oil/other stuff separated and then you checked your levels, it could read high and just be normal oil, since oil will eventually float to the top - but that takes days at the minimum in my opinion.

If your oil reading is really that high, and it's truly 100% oil - someone forgot to drain it when you had the oil changed. It's much more common than you would think, specifically if you (or whoever is doing it) is in a rush, tired or just done for the day - something that obvious can easily be overlooked (also common are double stacked filter seals, non-torqued drain bolts, even seen not removing the plastic from the new filter...).

All going to depend on what drains out of the pan.
 
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This all happened this morning and the oil was still clean. I did the oil change myself, definitely drained it, and only put in 6qt as usual.
Still has original head as far as I know. Bought in 2010 with about 120,000mi on it.
 
Clancy7007 said:
This all happened this morning and the oil was still clean. I did the oil change myself, definitely drained it, and only put in 6qt as usual.
Still has original head as far as I know. Bought in 2010 with about 120,000mi on it.
Click to expand...

If you got 216k miles out of a non-TUPY 0331 head you did pretty good. The one on my old '01 cracked at 102k
 
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zackcj7 said:
It's a 2001 one model right? Does it have the original 0331 head?
Click to expand...
2000 and 2001 TJs had the 0331 head, later (2002 or so) came the better/stronger TUPY version of the 0331 head.

I doubt yours will say TUPY but if it's there you should be able to see it by looking down through the oil fill hole on the valve cover.

Tupy through Oil Fill Hole.jpg

TUPY 331.JPG
 
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Soooooo.....
No water/coolant and only about 6qt in the pan (probably a little less). I'm confused and I'm going to order a pressure sensor.
Also not a TUPY.
 
I rough up the end of my dipstick with a little sand paper (😆). It helps me see the oil level better. It can trick you sometimes.
 
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