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post #1 of (permalink) Old 09-28-2005, 02:10 PM
Guido
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Oil PSI low

I have a 97 TJ 4.0. It's giving me oiling problems. It's my daily driver, and does fine on the road, but whenever I get off road, at low rpm, I lose oil pressure. On the road I generally have around 30-40 psi, and 15-20 psi at idle. At sustained low rpm (5-600) it goes down to zero. I have also noted lately that if I start the Jeep and let it run for a while at idle, it will get down to around 5 psi. This doesn't seem right to me. Any ideas on what might be wrong?
It doesn't make any strange noises or anything, but I am now afraid to wheel the damn thing.
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post #2 of (permalink) Old 09-28-2005, 03:44 PM
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Re: Oil PSI low

If the pressure were really zero the engine WOULD make noises, if not now then in a few minutes. Don't assume low oil pressure just because the factory gauge says so; they're notoriously unreliable.

Install an aftermarket mechanical gauge. Put a T in the block where the factory sending unit screws in. Reinstall the factory sender, and mount the mechanical gauge under the hood on a short piece of tube.

If the factory gauge is consistant (for example, always shows the true value minus 20 PSI, or always shows 60% of the true value) you can remove the aftermarket gauge if you want, but I wouldn't.

Isn't Palmer where they hold the state fair?
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post #3 of (permalink) Old 09-28-2005, 05:44 PM
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Re: Oil PSI low

Yep, the State Fair is held here every year.
I guess I need to get a mechanical guage then.
If it still shows as being that low, what would cause this? Bearings? Bad pump?
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post #4 of (permalink) Old 09-28-2005, 06:54 PM
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Re: Oil PSI low

[ QUOTE ]
If the pressure were really zero the engine WOULD make noises, if not now then in a few minutes. Don't assume low oil pressure just because the factory gauge says so; they're notoriously unreliable.

Install an aftermarket mechanical gauge. Put a T in the block where the factory sending unit screws in. Reinstall the factory sender, and mount the mechanical gauge under the hood on a short piece of tube.

If the factory gauge is consistant (for example, always shows the true value minus 20 PSI, or always shows 60% of the true value) you can remove the aftermarket gauge if you want, but I wouldn't.

Isn't Palmer where they hold the state fair?

[/ QUOTE ]

Good advice. Also don't assume you have good oil pressure because the factory gauge says so.
Posted a few days ago. A problem I had.

[ QUOTE ]
1988 YJ
302
New bearings rings and oil pump 1 year ago (ran fine in truck indicated middle of scale on oil pressure gauge when pulled out)
High volume oil pump
Otherwise stock
Holley oil pressure switch was shutting electric fuel pump off at idle (Holley indicates it should switch off at 6 PSI)
Jeep OP gauge was showing ~30 PSI hot at idle
Mechanical test gauge showed 5 PSI hot at idle [img]/ubbthreads/images/graemlins/thud.gif[/img]
Externally pump looks undamaged, shaft turns free
Pulled cover plate off oil pump, rotors look good but the relief valve is stuck ~1/3 open.
installed new oil pump 45 psi hot at idle. [img]/ubbthreads/images/graemlins/burnout.gif[/img]

[/ QUOTE ]

My experience with worn bearings is that the oil pressure will be OK at all times when cold but will drop radically at idle as the engine warms up. Let us know what you find.
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post #5 of (permalink) Old 09-29-2005, 07:49 AM
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Re: Oil PSI low

[ QUOTE ]
If it still shows as being that low, what would cause this? Bearings? Bad pump?

[/ QUOTE ]

Yep, or stuck relief valve like John said, or a clogged or defective filter. Main bearings are the usual fault. Cam bearings can also cause it, but that's uncommon. Rod bearings have no appreciable affect on pressure.
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post #6 of (permalink) Old 09-29-2005, 12:41 PM
 
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Re: Oil PSI low

try gettibg a new sending unit for the factory gauge
maybee its bad ??? something to try before you spend more money than you need too.. aftermarket gauge is always a good idea though
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