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Unread 09-13-2008, 03:10 PM   #1
StraightToPlaid
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Low oil pressure at idle

Ok, I just bought this jeep today and noticed this...

'97 Cherokee, 4.0L engine.

At idle the oil pressure will drop to 10 psi. I don't think my old '93 ever had it get that low. It looks like the sending unit had leaked in the past (old oil grunge from the sending unit down) and was replaced, the replacement doesn't look OEM though. At anything besides idle my oil pressure seems normal, about 40 psi with hot oil on the freeway.

I don't notice any noises when it's at idle, no valvetrain noise or anything like that.

Does this just sound like a flaky cheap sending unit or should I check to see if the oil pump is going out on me?

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Unread 09-13-2008, 03:17 PM   #2
CJ7-Tim
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The minimum 4.0 oil pressure specification is 10-13 psi, hot, at idle (750 rpm) with 10w-30 grade oil. The oil pressure gauge is not known to be very accurate.
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Unread 09-13-2008, 03:17 PM   #3
cowboy63b
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i am having the same problem with my 5.2 in my Grand Cherokee, sounds like a el cheapo was stuck in instead of oe, i just put a new sending unit in mine and it quit doing that, start with the cheap stuff first before you dive in to the engine, if that doesn't work have a qualified mechanic to do a oil pressure check, then go from there...
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Unread 09-13-2008, 03:20 PM   #4
1990JEEPXJ
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x2. just replace the sender and you will know your readings will be somewhat accurate. and 10 isnt out of the ordinary anyway. it should look like this:

http://thumbs300.1aauto.com/OSU/1AOSU00001.jpg
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Unread 09-13-2008, 03:21 PM   #5
StraightToPlaid
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Hmm, if the minimum is 10 it sounds like I'm in the clear even if it is accurate. It pops right up when I give it any gas at all so I'm not too worried. That cheap sender may not read well at low pressures.

I'll watch it carefully but it sounds like I may be in the clear until I can get a new sender. Looks like Rock Auto has them relatively cheap.
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Unread 09-13-2008, 03:47 PM   #6
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I think you are fine. You could alway switch to a manual guage since you plan on replacing the sender...that way you will know for sure what pressure is.
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Unread 09-13-2008, 04:16 PM   #7
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A friend's father is a mechanic at a jeep dealership, apparently he's been sitting around twiddling his thumbs because no new cars being sold means no warranty work. He said he'd hook it up to a manual gauge and check it out.
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Unread 09-13-2008, 06:29 PM   #8
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My 97 is about the same and it has 196,000 miles so I guess it won't be much of a problem plus I use mobil 1 to help
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Unread 09-14-2008, 02:34 PM   #9
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Mechanical oil pressure gauge is the best way to know for sure. Only takes a few minutes to check. Yes, the oil pressure sending unit (aka: oil switch in some parts stores) is a common failure. I've had best luck with replacement units directly from Jeep; seems to provide the best accuracy when mated with the factory gauge. Good Luck!
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Unread 09-14-2008, 04:22 PM   #10
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Quote:
Originally Posted by tjwalker View Post
Manual oil pressure gauge is the best way to know for sure. Only takes a few minutes to check. Yes, the oil pressure sending unit (aka: oil switch in some parts stores) is a common failure. I've had best luck with replacement units directly from Jeep; seems to provide the best accuracy when mated with the factory gauge. Good Luck!
Would autozone lend those?
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Unread 09-14-2008, 04:50 PM   #11
tjwalker
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They might; mechanical oil pressure gauge is a pretty common tool. Somebody should have one you can rent.
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Unread 09-15-2008, 03:09 PM   #12
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Just a note on mechanical gages:

You get what you pay for. I tried a cheapy unit ($13.00) and was alarmed when it read 5 psi at idle. I thought I was in for a main bearing job. A buddy of mine had a couple "brand name" high buck units and we threw them on to double check. The high buck gages showed a 15 psi idle. The guy who owns them is a stickler about his vehicles (semi-pro drag racer) and has his gages calibrated once a year, so they are good..................anyway, If I had believed the cheapo I would have been up to my ankles in a rebuild.........and I ditched the cheapo and got a 50 buck unit from Summit....Oh...I had just replaced the oil pump when this all went down........
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Unread 09-15-2008, 04:21 PM   #13
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Quote:
Originally Posted by hevybluzer View Post
Just a note on mechanical gages:

You get what you pay for.
Very good point! I always have purchased high quality tools, especially test equipment. You absolutely do get what you pay for. Lots of junk out there; buyer beware. Most rental equipment is "normally" pretty good quality stuff but just keep in mind that it doesn't generally get checked that closely or calibrated in-between uses
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Unread 09-16-2008, 07:50 PM   #14
StraightToPlaid
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I just got off the phone with the friend who's father is a jeep dealer mechanic. Apparently the factory spec allows the oil to go all the way down to 7 psi before it considers it a problem. I'm on the high side of 10 on the gauge so I'm fine.
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