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Unread 05-22-2012, 02:14 PM   #1
cherokeeman87
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Oil pressure

Have a 87 jeep Cherokee pioneer with the 4.0L inline six. When I start it up I have 60lbs oil pressure. Then it goes down to 25lbs. Brought it to the shop the mechanic tested it at 70lbs. So I installed a mechanical oil pressure gauge and still it drops dramatically. I think the oil pump may be acting up is there any way to check it without removing it.

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Unread 05-22-2012, 05:36 PM   #2
obfdcherokee
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Quote:
Originally Posted by cherokeeman87
Have a 87 jeep Cherokee pioneer with the 4.0L inline six. When I start it up I have 60lbs oil pressure. Then it goes down to 25lbs. Brought it to the shop the mechanic tested it at 70lbs. So I installed a mechanical oil pressure gauge and still it drops dramatically. I think the oil pump may be acting up is there any way to check it without removing it.
25lbs at idle is not bad it only requires 7 psi to avoid engine damage. Your pressure should go up and down with engine rpm. Keep in mind cold oil is harder to move than hot oil so your pressure will be higher at first start up.
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Unread 05-22-2012, 05:58 PM   #3
cherokeeman87
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Thanks that is encouraging to hear. Just worried a little
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Unread 05-22-2012, 06:09 PM   #4
obfdcherokee
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No problem. Glad I could help.
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Unread 05-23-2012, 08:23 PM   #5
Flyordie
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Quote:
Originally Posted by obfdcherokee View Post
25lbs at idle is not bad it only requires 7 psi to avoid engine damage. Your pressure should go up and down with engine rpm. Keep in mind cold oil is harder to move than hot oil so your pressure will be higher at first start up.
I will second this. Stock oil pumps aren't the greatest but they will work for what its lubricating. 13psi is the factory limit on the low side, 73psi is the high side I think.

Keep it between those 2 and you will do fine. :-)

Its only when you get the upgraded Melling pumps that you get better oil pressure. (Mine is 40psi idle, 64psi hwy when hot) or (65psi idle, 85-90psi @ hwy when cold, 50-60F or lower)
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Unread 05-23-2012, 08:43 PM   #6
Ross00TJ
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Less pressure equals more flow. The higher the pressure the less oil that is flowing through the oil passages, thus limiting lubrication, cooling, and cleaning.

An oil pump that gives more pressure would be a downgrade unless you mean better by low pressure, high flow...
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Unread 05-24-2012, 02:00 PM   #7
Flyordie
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Quote:
Originally Posted by Ross00TJ View Post
Less pressure equals more flow. The higher the pressure the less oil that is flowing through the oil passages, thus limiting lubrication, cooling, and cleaning.

An oil pump that gives more pressure would be a downgrade unless you mean better by low pressure, high flow...
I have the Melling High Volume oil pump in my I4. Its only higher on pressure because the pump is pushing more oil through than the oil passages can handle.

Literally, once the oil warms up, the pump is pushing so much oil through the lifter area that the pushrods are like a pressure washer for the valve cover. lol
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Unread 05-24-2012, 05:19 PM   #8
cherokeeman87
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I was always told the higher the pressure the better the seals and journals are. I have not worked on many jeeps yet but I own two Cherokees now.
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Unread 05-24-2012, 07:42 PM   #9
Ross00TJ
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For proper hydrodynamic lubrication there has to be a good balance between pressure and flow/volume. So some pressure is needed but if your oil pressure is at 50 or 60 psi at hot idle then you have an issue and the engine will not be getting the cooling and cleaning it needs.

What you perceive as a problem is perfectly normal and fine. Your oil pump is functioning as it should and your engine is getting plenty of lubrication, cooling, and cleaning.

You have nothing to worry about, engine oil wise anyways.
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