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Old 05-08-2013, 10:55 AM   #1
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Oil pressure

Hi all.... I have a 98 jeep wrangler and I noticed yesterday that my oil pressure was low... It's usually a little passed 40... When I drive the pressure is good but when I come to a stop it drops below 40... Press the gas and start moving it rises again... I have some blow back on my engine (on the dip stick and in areas around there... Oil was low yesterday so I added a qt. started it up and oil pressure was good but as the jeep warmed up and I came to a stop it dropped again.... Any ideas?

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Old 05-08-2013, 02:18 PM   #2
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The oil pump works harder at higher RPM's, thus increasing flow and pressure. Oil pressure at idle will almost always be lower at idle than at cruising RPM's and is normal. How much below 40 does it drop? What viscosity oil?

Oil is thicker (higher viscosity) when it is cold, which results in higher pressures also, warmer oil flows easier and your pressure will drop accordingly.

It doesn't sound like you have an oil pressure problem at all, how low does it get?

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Old 05-08-2013, 05:43 PM   #3
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It will start up between 40 and the hash mark after the 40... I usually put 10 w 30 in I have had a heavier oil in it till yesterday... The engine seems to be sounding fine when it's running but I do here a slight knock which I've had since I owned the jeep
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Old 05-08-2013, 05:44 PM   #4
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Missed your other question... It will usually drop to the 40 sometimes just a tad below the 40
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Old 05-15-2013, 11:23 PM   #5
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Mine is doing the same. Only mine drops WAY low and the light comes on. No ticks or nicks just low pressure???
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Old 05-15-2013, 11:43 PM   #6
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Missed your other question... It will usually drop to the 40 sometimes just a tad below the 40
The oil pump is mechanically driven by the motor, meaning as you speed up your oil pressure will increase. As long as the pressure doesn't drop way below normal or zero not too much can happen.
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Old 05-15-2013, 11:45 PM   #7
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Mine is doing the same. Only mine drops WAY low and the light comes on. No ticks or nicks just low pressure???
Does it drop to zero when your at idle or at a stop light? Sounds like a failing sending unit to me.
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Old 05-16-2013, 06:30 AM   #8
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Yes it does, them slowly rises and falls a little but stays way low
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Old 05-16-2013, 07:04 AM   #9
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Mine is doing the same. Only mine drops WAY low and the light comes on. No ticks or nicks just low pressure???
I would check it with a mechanical gauge first them get a new sending unit if it checks out fine. My 97 did that and I got an OEM unit from the dealer and all was good again.
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Old 05-16-2013, 07:17 AM   #10
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As above, verify your hot/cold/idle/2000 rpm pressures with a master gauge. Hot low idle can be in the 5-8 psi range, with 40 at high idle being acceptable.

Several things affect oil pressure: quality and type of lube, contamination, but mostly just engine wear. The seven main bearing six is very rigid on the big end, which gives it it's robust reputation. Despite that, like any engine, they can suffer bearing and journal wear resulting in lost or weak oil pressure.
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Old 05-16-2013, 07:40 AM   #11
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Note early TJs have an actual pressure gauge that will show fluctuations. Later models have basically a dummy gauge that will show a constant "good" pressure as long as it is range. (I don't know what year the change was)

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