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Old 04-14-2012, 01:54 PM   #1
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oil pressure gauge

My oil pressure gauge on my 97 TJ reads at 20 and wondering if something might be wrong. I've always thought it should read at 40

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Old 04-14-2012, 02:00 PM   #2
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Because the oil pump is engine driven, the oil pressure rises and falls in direct step with engine rpms. 20 lbs. of oil pressure at idle is very good, and it rising higher at higher engine RPMs is normal. A good rule of thumb for oil pressure is acceptable 10 psi per 1000 RPMs.

On newer TJs, that is not the case since newer oil pressure gauges no longer indicate the true oil pressure. They tend to move to mid-scale and stay there so as to not unnecessarily alarm those who don't know how oil pressure is supposed to work.

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Old 04-14-2012, 02:10 PM   #3
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Ok thank u, when driving going about 40 mph it stays at 20 lbs, is that still ok? I just bought the jeep and got it drive able and today is my first time driving it
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Old 04-14-2012, 02:50 PM   #4
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Oil pressure depends on engine RPMs, not your MPH. If your oil pressure never gets below 10 at idle and it rises above 20 as you accelerate to higher engine RPMs, it sounds normal. If you're only shifting at 2000 RPMs, thats a bit too low of an RPM to shift at except in town. Wind the engine up to over 3000 or to 4000 RPMs as a test when getting onto the highway and see if the oil pressure rises up above 20 as it should. If your gearing and tire size is such that your engine RPMs are only 2000 at lower speeds and your oil pressure is 20, that's normal.
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Old 04-14-2012, 08:35 PM   #5
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Ok thank you for the info
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Old 04-14-2012, 10:00 PM   #6
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Just how low of a drop at idle is acceptable? My 4.0 drops almost to 0 and then rises to about 7-10 at idle. I just put a direct pressure guage on it to make sure it wasnt the sending unit and it still drops. The engine doesn't make a sound though! No knocking or ticking! Should I be concerned?
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Old 04-15-2012, 08:14 AM   #7
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Any suggestions? Should I just drive it?

I see several bolgs stating it could be the cam shaft bearings! If so does anyone know of a step by step for changing while engine is installed?
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Old 04-15-2012, 09:20 AM   #8
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Ok thank u, when driving going about 40 mph it stays at 20 lbs, is that still ok?
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Old 04-15-2012, 09:53 AM   #9
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Change the oil sending unit its a $25 part. Should fix your problem, just changed mine the alarm kept coming on for low oil pressure. This is a common problem.
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Old 04-24-2012, 07:35 PM   #10
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My Low Oil Pressure Tale
I just got a 2004 Rubicon 4.0L six about a month ago. It has 73K miles on it. Everything seemed fine until I had the oil pressure gauge take a dive when I was driving home from work. Needless to say I was freaking out. I brought it back to the place I bought it from but everything was fine while I was there. First thing I did was change the oil pressure sender. Was good for about a week, then it did the same thing. Always when the engine was hot, after more than 1/2 hour drive. I had the mechanic put in a mechanical gauge. I had the oil pressure dropping down to about 3-5 PSI at low idle. Never made any noises, and as soon as the idel was up, the pressure would jump up to about 35 to 40 at 1500 rpm. Spec is 13 PSI at low idle minimum. The dealer mechanic had me bring it in and they changed the oil. Apparently they used 5W30 as their standard oil. They bumped it up to 10W30, and things were much better. I still get a bit of a low pressure at very low idle with the engine hot. Now about 10 PSI at probably 600RPM. I had a SunPro installed. I noticed a bunch of air in the plastic oil line. Called up Sun and they told me it needed to be bled after installation. They said the pressure would read a bit lower that it really was due to the compression of the air in the lines. I have to bleed it, but looks like the change in oil also helped out my situation. The stock oil gauge is crap. The only time it moved was when there was 3 PSI of oil pressure, otherwise it read a bit above mid scale all of the time. Damn those idiot gauges.I would be very careful about relying on the stock gauge.

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