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Old 02-25-2012, 08:45 PM   #1
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Oil Pressure concerns

I picked up a new to me '98 TJ with 123K miles.
On the 600 miles drive home, I once noticed the oil pressure had dropped to 20 psi. I had been running 40.
I stopped for gas and it was back up to 40.

It was fine all the way home. When I stopped in the driveway to open the garage door I turned it off.
When i started it I had a check gauges light and 0 oil pressure.
I let it sit for 30 minutes, started it, initally had a check gauges light and 0 oil pressure
After about 5 seconds the oil pressure slowly started to climb and the check gauges light went out.

Do I have a brewing problem?

Thanks in advance

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Old 02-25-2012, 08:54 PM   #2
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Common issue with TJs. Most likely not a true low oil pressure, just a bad sending unit sending false readings to the gauge. A cheap and easy fix.

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Old 02-25-2012, 09:21 PM   #3
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Mine does it occasionally as well. When I first start the jeep my check gauges light comes on and some times it will just turn off and sometimes as soon as the jeep moves even a millimeter it will go off. It may do this 1 of 10 start ups. I don't worry about it.
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Old 02-26-2012, 06:36 AM   #4
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Change the sending switch first, it's a cheap test.
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Old 02-26-2012, 07:22 AM   #5
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I wouldn't be driving it around until you are sure it is not the oil pump. Mine did the same thing a few years ago and it was the oil pump. It went out in my 97 at about 140,000 miles. However, as the others have said above it could be the sending unit also. I just replaced my sending unit about a week ago because it was spraying oil all over the place. This is the unit I purchased from napa (NAPA AUTO PARTS). I have the 4.0, I am not sure if it is the same unit for the 4cly.
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Old 02-26-2012, 08:48 AM   #6
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Thanks guys, it is the 4.0 I6.
Does someone have a DIY on the oil sending unit replacement.
I've done on my '01 Corvette and that is a challenge because you have to remove the intake manifold.
Where is the unit located on the I6 ?
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Old 02-26-2012, 09:39 AM   #7
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Right by the oil Filter. I put a T on it and ran a real mechanical pressure gauge. When the dash goes to 0 I look at the real gauge. No where near 0......
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Old 02-26-2012, 09:47 AM   #8
Knows a couple things...

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Quote:
Originally Posted by Fortune View Post
I picked up a new to me '98 TJ with 123K miles.
On the 600 miles drive home, I once noticed the oil pressure had dropped to 20 psi. I had been running 40.
I stopped for gas and it was back up to 40.
That is not a problem, in fact that is excellent oil pressure and is exactly how it should be.

Oil pressure is generated by a mechanical engine driven oil pump. The faster the engine turns, the more oil pressure is generated... so a lower oil pressure at idle and a higher oil pressure on the highway is normal and the way it should be.

A good rule-of-thumb for acceptable oil pressure is 10 psi per thousand engine RPMs.

Because too many people were unnecessarily alarmed by the TJ's oil pressure gauge showing the true oil pressure and it's normal ups and downs, Jeep engineers dumbed the gauge down in the early 2000's so it only shows a mid-scale indication if everything is ok. This is a phenomena that has only happened since cars stopped coming with oil pressure gauges like they used to. Not many people still know that oil pressure is supposed to vary up and down with engine RPMs.
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Old 02-26-2012, 11:10 AM   #9
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And since many people do not ever look at their gauges they have to have a idiot alarm to tell you to look when something is wrong. But having 4 grown kids driving and not able to be with them all the time that may be a good thing.
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Now in a 04 TJ 4cyl 5spd CV @120K+
Both as a commuter vehicle in NW, NJ
April 2012.downsized and now a 99er.
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Old 02-26-2012, 08:05 PM   #10
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Thanks again guys.....
Rich

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