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Old 07-15-2014, 09:19 AM   #1
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low oil pressure

Hello everyone. I have a 97 jeep tj 2.5l. Recently I have been having my check gauges light come on after driving my jeep for extended periods of time. My oil pressure reaches 0 but when I'm driving it will shoot back up to around 35. It seems to be running perfectly fine and Im not seeing any differences in how the jeep runs. After reading posts on the forum I thought it was the oil pressure sensor. I bought one from Napa and it didn't help. I returned it and went to the dealership and bought one there with no luck. My question is that if there is anything else that I should look at before I go on and buy an oil pump? Thanks everyone.

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Old 07-15-2014, 10:23 AM   #2
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How many miles are on your Jeep. If you have high mileage, >180k, then your main bearings are probably worn and replacing the oil pump alone won't help by itself. If you replace the pump, you should inspect and replace your main bearings (they are probably your real problem) at the same time. That will give you another 100k miles on that motor.

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Old 07-15-2014, 11:28 AM   #3
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Stupid question but if my pump was bad shouldn't it say at the same oil pressure?
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Old 07-15-2014, 11:42 AM   #4
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I was told it could be the fuse for gauge as I have the same issues.
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Old 07-15-2014, 11:45 AM   #5
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Ya I just don't want to go through all of this and spend the money if it's something simple. If my bearings are worn should my engine be ticking or making noise?
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Old 07-15-2014, 11:47 AM   #6
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Before you do anything, change out the sending unit.
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Old 07-15-2014, 11:54 AM   #7
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I I already replaced the oil pressure sending unit twice
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Old 07-15-2014, 12:15 PM   #8
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Have you tried changing oil since this happened? Dirty or low oil might cause this problem. Plus it never hurts to have fresh oil.
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Old 07-15-2014, 12:17 PM   #9
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I changed it 400 miles ago
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Old 07-15-2014, 12:18 PM   #10
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Quote:
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I I already replaced the oil pressure sending unit twice
Sorry, didn't read. The symptoms remained the same throughout every sending unit?
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Old 07-15-2014, 12:20 PM   #11
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Did you change weights perhaps?
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Old 07-15-2014, 12:30 PM   #12
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Symptoms were the same. I have always used 5 W 30
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Old 07-15-2014, 12:52 PM   #13
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At first I bought a sensor from Napa and then read some forums that stated that these are not good to use and I should buy from the dealership
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Old 07-15-2014, 02:48 PM   #14
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Not too sure if our engine are similar but I have a 00 4.0L with what I believe to be worn cam, main, rod bearings. Currently I'm using M1 15W-50 oil as a band aid fix to give it slightly better oil pressure.

Sooner than later I'll put a mechanical oil pressure gauge on the Heep a long and see what is going on because you can never be too sure about how accurate the OEM gauge and sending unit is.
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Old 07-15-2014, 02:56 PM   #15
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Quote:
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Ya I just don't want to go through all of this and spend the money if it's something simple. If my bearings are worn should my engine be ticking or making noise?
Not for the low oil pressure issue. When you oil is cold and thick it can maintain pressure. As it heats up and viscosity drops it is not maintained it between the bearing and the crankshaft and you get the low oil pressure at idle. It jumps up as soon as rpm increases because the oil pump is good and can increase volume as rpm increases.

Eventually the mains will start to knock but you have some time to change them. It isn't an emergency.

Of course, like everyone says, verify that it isn't a gauge or sending unit. You can only really do that by hooking up a mechanical (wet) gauge.
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Old 07-15-2014, 02:57 PM   #16
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Okay so I cant be positive, hopefully a more seasoned veteran can chime in but I thought the oil pressure gauge was a dummy gauge on the TJ? Check gauges light is typically for when the jeep over heats, at least thats when I've seen them pop on (not on mine thankfully lol), and no lose of performance kind of reaffirms it may not actually be legit. Have you hooked anything up to the OBD port to check actual readings..?
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Old 07-15-2014, 02:59 PM   #17
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Are you saying its zero at idle and then goes up to normal when running? I had that problem, with my 97 Wrangler 4.0L, and it was the sending unit.
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Old 07-15-2014, 03:35 PM   #18
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I'm not getting a check engine light but I will hook up my old reader after work. And yes its at 0 idle and around 40 when actually driving
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Old 07-15-2014, 08:35 PM   #19
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I had the same problem with my 2.5. The pump RPM can overcome the low oil pressure. I actually found my oil pump gasket was mispositioned between the pump and block. I replaced the oil pump. My pressure stays around 10 psi at hot idle now. I did have a lifter collapse shortly after and it started ticking. I replaced all the lifters and I run 20W50 oil. It still runs 10 psi at idle but has 173,000 miles on it.
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Old 07-15-2014, 10:02 PM   #20
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Okay so I cant be positive, hopefully a more seasoned veteran can chime in but I thought the oil pressure gauge was a dummy gauge Check gauges light is typically for when the jeep over heats, at least thats when I've seen them pop on (not on mine thankfully lol), and no lose of performance kind of reaffirms it may not actually be legit. Have you hooked anything up to the OBD port to check actual readings..?



Sometimes "yes" and sometimes "nope" .......... I could be wrong but I have read that once upon a time it was more accurate. I'm not sure of the year break and engine size.
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Old 07-15-2014, 10:20 PM   #21
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Check gauges light comes on for sure with low oil pressure reading. I've seen it many times in the 20 years I've been a jeep/dodge tech
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Old 07-16-2014, 11:20 AM   #22
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I have close to 300,000 miles on my engine with great oil pressure.

If your oil pressure is intermittent it can only be one of 2 things.
And you already did one of them.

#1. Oil Pressure Sender. Fix, Change Sender
#2. Oil Pressure Relief. The do get varnished with mileage. Fix, Change Pump.

I went with a High Output pump, but I like great oil pressure under all circumstances.

The pan on Jeeps are easy to drop, if you have basic mechanical knowledge, buy the green 'Plasti-Gauge' at your local auto parts store and check the clearances of your rod and main bearings.
If the tolerance is greater than .002 and the crankshaft bearing journals are not scored replace the bearing inserts, .001 oversize are available if necessary. You will probably only find the Rod Bearings worn to excess with your mileage, it's one of those things, "while I was there"
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Old 07-16-2014, 11:36 AM   #23
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Originally Posted by NFGZ View Post
Okay so I cant be positive, hopefully a more seasoned veteran can chime in but I thought the oil pressure gauge was a dummy gauge on the TJ?
Not true in early TJs like yours, that didn't happen until later maybe 2001 or 2002 or so.
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Old 07-16-2014, 11:51 AM   #24
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I appreciate everyone's input! Could it just be an issue of using a lighter oil weight. Everywhere I'm reading is saying I should use 10w30 instead of 5w30
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Old 07-16-2014, 01:28 PM   #25
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A 5W-30 is fine, it and 10W-30 both have the same 30 viscosity when warmed up.
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Old 07-16-2014, 04:42 PM   #26
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If the gauge says no pressure, assume till you know better, there is no pressure,

ya really need to investigate the problem before you cause any or any more damage,
It still may be salvageable.
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Old 07-16-2014, 04:53 PM   #27
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Roughly how long and difficult is an oil pump change
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Old 07-16-2014, 06:01 PM   #28
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It took me 2 hours in my driveway. It's pretty easy.
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Old 08-08-2014, 01:56 PM   #29
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Hey everyone I figured I would do an update on my low oil pressure issue. Sorry it took so long I was on vacation for 2 weeks. I went to the auto parts store and bought a mechanical gauge for $20 and installed it permanently. The gauge runs between 14 and 40 while the engine is hot. I assume that there was just a problem with the sensor or the wiring somewhere. If anyone else is having the same issue I definitely recommend getting a mechanical gauge first and checking it out before going through all of the trouble changing the oil pump. Thanks everyone for all the insight on this issue.
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Old 08-09-2014, 02:25 AM   #30
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May sound like a stupid question but how much oil did you put in when you changed it? Does the dipstick read full?

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