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Old 08-31-2010, 05:22 PM   #1
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Today my oil pressure was in the 20s is this ok? it's usually around the low 40s but today I noticed it wasn't. what can I do to fix this?

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Old 08-31-2010, 06:32 PM   #2
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Oil pressure varies up and down in direct step with engine rpms and its temperature. The colder the oil is, the higher the pressure the gauge will show (newer TJ oil pressure gauges excepted, they were reprogrammed not so show varying oil pressure). And the higher the engine rpms, the higher the oil pressure will be. That is because the oil pump is engine driven.

10 psi per 1000 engine rpms is a good rule of thumb for acceptable oil pressure.

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Old 08-31-2010, 07:41 PM   #3
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Replace the sending switch and go from there. It's cheap and they go bad often.
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Old 08-31-2010, 07:50 PM   #4
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ok thanks
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Old 09-07-2010, 09:06 AM   #5
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I have a just-bought 02 TJ X 4.0 (65k miles) and have been noticing my oil pressure gauge intermittently reads pegged out @ 80psi. I haven't noticed a significant difference in performance when this happens except that I had a hard time keeping it at 75mph on a low-grade long incline on the interstate unless I dropped it into 4th. (i initially put that on the crap stock gear ratio ~ 3:07 while running 31s; but could be related to the oil pressure? not sure. anyway)
When I see that the OPG is pegged, I usually put it in neutral and kill the engine, coast for a couple of seconds, and then fire it back up; it cures the pressure issue every time. I can't tell if it's a faulty gauge or something more serious. I checked the oil level (fine) and it had a fresh change @ the dealership just prior to my purchase, so a blocked filter isn't the problem.
Sorry for such a long post on a single issue, but anyone have any ideas?
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Old 09-07-2010, 10:07 AM   #6
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Quote:
Originally Posted by BigEZ View Post
I have a just-bought 02 TJ X 4.0 (65k miles) and have been noticing my oil pressure gauge intermittently reads pegged out @ 80psi. I haven't noticed a significant difference in performance when this happens except that I had a hard time keeping it at 75mph on a low-grade long incline on the interstate unless I dropped it into 4th.
Shifting out of overdrive into 4th gear for a long grade should be considered normal and the correct thing to do to prevent the engine from lugging. If you notice the '02 TJ has less performance as another TJ you have driven, it could be nothing more than the 02 may have a higher axle ratio like 3.07 instead of the better lower 3.73 ratio that gives better performance on the highway, especially on grades.

So far as an erroneous oil pressure indication goes, the usual culprit for that is a bad oil pressure sender which is easily and inexpensively changed.
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Old 09-07-2010, 10:08 AM   #7
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I would replace the oil sending switch before pointing the finger at something else. They are cheap and easy to do.
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Old 09-07-2010, 04:06 PM   #8
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Originally Posted by Jerry Bransford View Post
Shifting out of overdrive into 4th gear for a long grade should be considered normal and the correct thing to do to prevent the engine from lugging. If you notice the '02 TJ has less performance as another TJ you have driven, it could be nothing more than the 02 may have a higher axle ratio like 3.07 instead of the better lower 3.73 ratio that gives better performance on the highway, especially on grades.

So far as an erroneous oil pressure indication goes, the usual culprit for that is a bad oil pressure sender which is easily and inexpensively changed.
Does the different axle ratio affect anything else or just highway preformance? (just got a 2002 tj)
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Old 09-07-2010, 04:23 PM   #9
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Does the different axle ratio affect anything else or just highway preformance? (just got a 2002 tj)
Not so far as the R&P gears themselves go, at least not significantly... really just the overall performance and engine rpms.
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Old 09-08-2010, 01:43 AM   #10
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thanks. This is my first wrangler, but i have had 2 4.0 Cherokee classics, one a 2WD 5 spd, and the other a 4WD auto, and neither one had any highway speed issues. Sure the auto would downshift from time to time but nothing too noticeable. My next mechanical upgrade was going to be gears...what is recommended? I'm running 31" GY Duratracs, on D30/35 differentials. I've seen the charts but would like some anecdotal testimony. I want it to be trail worthy but not top out at 70mph either. 3:73s? 4:10s? front or rear?
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Old 09-08-2010, 01:45 AM   #11
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thanks. This is my first wrangler, but i have had 2 4.0 Cherokee classics, one a 2WD 5 spd, and the other a 4WD auto, and neither one had any highway speed issues. Sure the auto would downshift from time to time but nothing too noticeable. My next mechanical upgrade was going to be gears...what is recommended? I'm running 31" GY Duratracs, on D30/35 differentials. I've seen the charts but would like some anecdotal testimony. I want it to be trail worthy but not top out at 70mph either. 3:73s? 4:10s? front or rear?
For what vehicle, model year, engine, and transmission? And you always need to regear both axles to the same ratio. Will you ever be going to a larger tire size than 31"?
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Old 09-09-2010, 02:35 AM   #12
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02 4.0 5spd. It will be awhile, but eventually I might go as big as 33"s.
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Old 09-21-2010, 06:39 AM   #13
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To continue this thread... I have changed the sending switch and it continuses to work until the engine is really warmed up (running for approximately 10-15 minutes. While i am moving, it is fine, when I get to a stop light and idle, it drops to 0. Where would you go next after replacing the sending switch? I hope it is not the oil pump, but I am prepared for the worst.

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Old 09-22-2010, 12:39 AM   #14
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oil pump shouldn't be too hard to replace. If I recall my 2000 Cherokee also bottomed out at low idle; soon as I hit the gas it shot back up to 40. just the way it was. never had any probs with it. here is a quickshot useful (?) link:

Jeep 4.0 Oiling System Upgrades
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Old 09-22-2010, 08:48 AM   #15
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I didn't see where the OP had verified correct oil level?
If correct, I would put a mechanical guage on there and verify, and also look at changing the oil and filter.
Check the easy stuff before tearing the engine apart.
FWIW, my '98 with 138K on it runs (according to the factory guage) 19-22 hot idle right off the freeway and 42-50 above 1500 RPM-that's with 10/30 Valvoline syn. and a Wix filter.

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