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Old 08-25-2014, 09:10 AM   #1
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Lower Oil Pressure

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Old 08-25-2014, 09:11 AM   #2
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This is after driving 30 miles to work.

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Old 08-25-2014, 09:17 AM   #3
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I guess I need a mechanical gauge to verify pressures. However it's kinda looking like I need to look into replacing my main bearings.

I've had 2 cracked heads (an original 0331 casting and a replacement 0331) before replacing with a new one from Clearwater Cylinder Heads. Usual cracked spot each time resulting from a crankcase full of antifreeze. I'm thinking they (the bearings) have been damaged.

Has anyone else had pressure this low?
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Old 08-25-2014, 09:38 AM   #4
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i'd replace the oil pressure sending unit, they are pretty cheap. not sure what year you have, but many of the gauges are dummy gauges and dont read very accurately even when functioning at 100%

it is normal to have very low oil pressure at idle when the vehicle is warm, as long as it still goes up with rpm's
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Old 08-25-2014, 10:00 AM   #5
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It's a 2000 Wrangler 4.0.

It's an "active" gauge. After the engine is warmed up and I take off from a start it gets to about 20psi and stays there until I come back to idle.

However if I park it for 5-10 minutes and start it back up, it'll jump up to about 35psi and then revert back to the 5psi-20psi dance.
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Old 08-25-2014, 10:10 AM   #6
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What oil/filter are you running?

Once you confirm the numbers with a mechanical (ruling out the sending unit being bad). changing to a slightly heavier oil will help. Also, some have reported certain brands of oil filters seem to give them lower PSI. Basically as long as you're maintaining ~10psi/1k RPM you're "good" in theory.

FWIW, most run 10w30. I went with 10w40 and my pressures are better.
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Old 08-25-2014, 11:01 AM   #7
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Quote:
Originally Posted by mrcarcrazy View Post
What oil/filter are you running? Once you confirm the numbers with a mechanical (ruling out the sending unit being bad). changing to a slightly heavier oil will help. Also, some have reported certain brands of oil filters seem to give them lower PSI. Basically as long as you're maintaining ~10psi/1k RPM you're "good" in theory. FWIW, most run 10w30. I went with 10w40 and my pressures are better.
Running Castrol 10W30 oil. I'm not certain but my mind is telling me it's a Bosch.

The next time I change it I'll give 10W40 a chance and see how it goes. Any recommendation on filters to use / avoid?
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Old 08-25-2014, 11:07 AM   #8
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Before doing anything expensive or going to a heavier than necessary oil, just replace the oil pressure sender with a new Mopar sender. I would avoid aftermarket senders like AutoZone sells, they tend to have too many problems. I got two (might have been three) bad replacement oil pressure senders in the same day from AutoZone years ago before I wised up.
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Old 08-26-2014, 07:11 PM   #9
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Jerry, I'm curious about you changing an oil pressure sending unit two, maybe three times in a day. After changing one today, I want to know how many beers it took to convince yourself you wanted to do it? I'd rather opt for an elective root canal.

Changed the sending unit out with one from the dealer and I'm still having low oil pressure at hot idle. Several times on the test drive it bottomed out at stop lights.

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Old 08-26-2014, 07:16 PM   #10
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sorry, this is a dumb question, but have you checked your oil level?
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Old 08-26-2014, 07:18 PM   #11
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Without a mechanical gage on there you really don't know what kind of pressure you have.
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Old 08-26-2014, 07:29 PM   #12
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Earlier TJs like the OP's 2000 have a true oil pressure gauge. It was only after around 2002 or so when Jeep went to a gauge that keeps the pointer centered if the oil pressure is otherwise ok. Electrical gauges can be every bit as accurate as mechanical gauges if not more accurate... look in the cockpit of modern aircraft and space stations that use analog instrumentation and gauges driven by senders and digital electronics.
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Old 08-26-2014, 07:32 PM   #13
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sorry, this is a dumb question, but have you checked your oil level?
Just replaced the cylinder head a week ago. Have checked the levels of coolant and oil daily since.
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Old 08-27-2014, 05:19 PM   #14
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I know my engine did not have any low oil pressure problem ( I read 10-13psi @ hot Idle is normal). jumps up from there as RPM's increase. My sending unit converts resistance into PSI reading at the gauge on my 98 TJ. A manual gauge will give you the real scoop. I remember a long time ago a Ford TSB came out for a specific yr w/psi oil gauge that read articically low from the factory (new) the fix was to wire in a certain size resistor (Radio shack 20 cent item). Not saying to try/do this-just saying for your piece of mind check with a manual gauge/hose/fiting. Then you will know for sure. I replaced my sending unit because it was 15yrs old, and read low(like what would have been 5-6 psi range/scale on gauge) The new one does operate the gauge at a slightly higher range. Also usually if oil psi is really low at hot idle (<5psi)you will hear lifters click and/or slight rod knock.

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