1996 Jeep Grand Cherokee V-8 134000 miles

DONKEN

MEMBER
1996 JEEP CHEROKEE

From cold start oil pressure goes to 40 pounds. After running for 10-15 minutes slight tapping is heard from passenger side of engine block. Tapping gets louder and oil pressure slowly drops to 10-12 pounds at idle. When engine is revved to 10-12 thousand, pressure climbs to 40 psi. Oil is changed every 3000 miles and quality oil for high mileage vehicle is used. Would think it is a hydraulic lifter problem, but symptoms are backwards. Any ideas?

2 Replies

2CARPRO JACK

MECHANIC
11,533 POSTS

Could be bearing clearance problems or maybe just a weak oil pump. Install a manual oil press gauge to verify accuracy of the pressures. Then its most likely time for tear down and inspection

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Tuesday, January 2nd, 2007 AT 10:00 AM

MATHIASO

MECHANIC
1,209 POSTS

Worn or sticking valve lifters may cause a clinking noise at low speed, specially when the engine is warming up, but you heard a taping noise and you are loosing oil too?
Let me help you to diagnose and locate that noise:
You need a stethoscope to amplify the noise.( Cost very little money)
start your car, open the oil filler cap and listen through the opening. This may give you an indication of clogged lifter or excessive valve clearances.
Listen at each intake and exhaust manifold runner, a valve that have excessive clearance or very worn guide will be detectable and isolated( DO NOT PLACE THE STETHOSCOPE ON THE VALVE COVER OR HEAD BOLT)
Listen at the fasteners holding the valve cover, noises that appear to have a frequency rate less than the speed of the crankshaft indicate a camshaft related problem this includes the valve drive train, mechanical fuel pump, oil pump and distributor.
If noises appear in this area, start checking your oil pump with a oil pressure gauge.
Noise occurring at the same rate as the crankshaft rotation can be caused by piston slap, loose piston pins, worn connecting rod bearings and worn main bearings.
Once the problem is isolated, it will be up to you to do the tear down or take it to a mechanic.

Good luck :)