Intermittent Low Oil Pressure

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SuperSpore

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1990 Tbi 350.
I experienced low oil pressure for ab0ut 30 minutes while driving. it dropped from the normal 30-40, to the first hash mark on the half moon gauge which seems to be about 15.
At first I stopped, turned the truck off then on and the pressure returned to the normal 30 at idle for a while.
But about 15 minutes later it dropped to 15 again. 20 minutes later on the freeway, it just jumped from 15 to 30 and stayed there.
Took it to for an oil change the next day, and it stayed normal. (It went up a few psi.)
Any thoughts? Is it possible the filter was blocked?
What are the symptoms of an oil pump going bad?
Thanks.
 

name

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I got the same thing going on with my '94 5.7, solid 40 psi when running and drifting down to 18-30 ish psi when idling. It will also occasionally dip down ( hard fluctuiation ) to about 8 psi but then snaps back up quickly. I replaced the sending unit and cleaned the connector but it made no difference. I do noticed it works better with clean oil and new filter so I don't let it worry me much cause I figure it is sensor related. never heard a knock or a lifter tick so I figure I'm good.
 

AuroraGirl

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I got the same thing going on with my '94 5.7, solid 40 psi when running and drifting down to 18-30 ish psi when idling. It will also occasionally dip down ( hard fluctuiation ) to about 8 psi but then snaps back up quickly. I replaced the sending unit and cleaned the connector but it made no difference. I do noticed it works better with clean oil and new filter so I don't let it worry me much cause I figure it is sensor related. never heard a knock or a lifter tick so I figure I'm good.
if i were you i would do an oil pan gasket if it leaks and see if you got some sludge build up and if you do, may be wise to try to gently flush or frequent change it out of there but i would try a sender and check the wiring before that for sure
 

GoToGuy

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You can do actual diagnostics or you can guesstimate and radomly replace parts, and it's this evan though i replaced it with new. A blocked filter? As in never changing a filter or you engine is making some much debris in the oiling system? If the filter material no longer flows oil, it would in continuous bypass. Our oil filters are not full flow. Our oil filters are in bypass above a preset psi. Therefore a " blocked filter " would have no effect on system pressures. An oil pump showing it's age can have big effect on oil pressues. There are no seals internal. Just metal to metal clearence. As gears an surfaces wear those clearances open and pressure tapers off, and partial oil circles within the pump rather than pressuring oil system. Small areas of wear within the engine all add up. A half to one psi drop along the cam bearings, one psi at each main bearing. Wear on the pump gears and flat surfaces. A hot Calif day " what 10 psi ? ". The service states a minimum 6 psi at idle is acceptable. Good luck.
 

stutaeng

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Hook up a mechanical guage. The cluster guage is as good as a low, medium, and high precision.

15 on the cluster guage does not equal 15 "psi."

Maybe it was low on oil before the oil change. My truck had a weird issue where the oil pressure would dip low when I took off from a stop. Turns out my oil level was low. Truck is a leaky mess.:doh2:
 
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