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Old 04-01-2012, 07:45 PM   #1
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Odd Oil Pressure 97 4.0L

On my way home tonight I noticed the oil pressure going from alittle over 20 and dropping down to about 10 then up over twenty again and then down to 10 or alittle less. This was driving down the road at 55mph and around 1600 rpm. At idle it was be at 10 or so then at the next stop idleing it might be around 20. I searched but didnt find anything else really like this where it jumps around like this when warmed up. I just did a oil change with 1 quart lucas oil additive. This my oil pump going or sending unit?
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Old 04-02-2012, 05:17 AM   #2
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Id check your oil pressure with a mechanical gauge first and go from there.. Then you can make a better determination as to what's happening

Apache chief, e ne chuk!
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Old 04-02-2012, 06:08 AM   #3

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Mechanical gauge is the way to go but I have replaced the sending unit on 2 of my TJ's for similar reasons. I would go with an OEM sending unit from the dealer. More expensive but I have had better luck with them.
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Old 04-02-2012, 07:39 AM   #4
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Mine does the same thing, it is totally crazy but it is fine. I need to get around to replacing the sending unit but it isn't a big deal. I have my check gauges light comes on sometimes because the sending unit gets stuck. As soon as the vehicle moves the gauge works and the light goes off. It doesn't do this all the time but another clear indication I need to replace the sending unit.
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Old 04-02-2012, 08:03 AM   #5
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I don't know how the oil pump on a Jeep works, but on SOME oil pumps, the impeller is driven by a key in the shaft (usu. a distributor shaft). So if the key breaks, or the keyway breaks out of the impeller, it will work just fine until it slips. Then it will not develop proper pressure, until (unless) the broken-off key snags its other half again, when it will work again. Sooner or later it will just fail outright.

I don't think I'd ignore this. It could get expensive.

BTW -- is the oil level OK ? That could cause a similar symptom.
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Old 04-02-2012, 08:31 AM   #6
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Oil level is good I just changed it. Im going to get a sending unit today as a first step. If these are notorious for going bad then with 112,000 miles now Im hoping thats what it is.

2000 Sport 4.0, 5 speed, 8.8 rear end, gears, 4in lift, 35s
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