Mechanics

CHEVY LOW OIL PRESSURE

1994 Chevrolet Silverado

Engine Mechanical problem
1994 Chevy Silverado V8 Four Wheel Drive Automatic 379000 miles

I've been getting low oil pressure for about 2 weeks now. For the most part on the highway it is a little low, approw 25, but at an idle goes to almost 0 and the light comes on. In the morning it would take about 10 seconds to get any pressure. Changed the sensor for the gauge and checked with a mechanical gauge no help. Did an oil change and got pressure right away, and good pressure but that went away after an hour on the highway I got off the pressure went to about 2 but when I got into the gas it would go up. So I pulled the oil filter and the new oil was very dark and thin but the oil on the dipstick still looked new. Engine was running good when in the gas and was ideling OK.
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Ninja181
February 15, 2010.




When you used the mechanical pressure gauge, did it read low too? Also, when you changed the oil and got good pressure for a short time, did you also change the filter at that time? Have you tried an engine flush? I'm a little confused as to how the oil could be dirty when drained, but clean on the stick.

When the pressure drops to 0 or very low, do you hear any ticking or knocking in the engine? Finally, is this the original engine with 379K on it?

Let me know.

Joe
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The mechanical gauge read 23, there is some tapping when low (the light is on) sometimes. When I changed the oil I did change the filter, and after got oil pressure right away, didn't have to wait about 10 seconds like before. It is the original motor and when the oil pressure drops to where the light comes on there is sometimes some tapping. The dirty oil was only in the filter.

Tiny
Ninja181
Feb 16, 2010.
Did 2 engine flushes and during the second as the engine built up temp the oil pressure did start to drop and went into the orange warning but during the start up of both flushes I had about 45 lbs of pressure and after about 10 mins on the second flush went to 5 lbs at an idle in park ( no tapping sound). As far as I can tell the oil and the filter look clean.

Tiny
Ninja181
Feb 16, 2010.
If you are holding 45psi at start up, then the bearing in the engine are still good. My concern is the ticking you get. That sounds like a lifter when the pressure gets too low. If you can, now that you have a new filter and oil, I would like you to use the mechanical pressure gauge again. If it read 23PSI on the mechanical one, that is good. Have you tried replacing the oil sending unit?

Here is something to think about. When metal gets hot, it expands. Because of that, the pressure should increase when it warms up and not drop. At this point, I feel you either have a bad sending unit or the pick up tube screen on the oil pump is partially plugged. The ticking has me concerned, but if really had 0 psi of pressure, you would hear rod and bearing knock too.

Check it out with the mechanical gauge, and you may want to replace the sending unit. It is a cheap part and easy to replace.

Let me know what you find.

Joe
PS: When you change the oil, always replace the filter too. With the detergent in the oil, basically it cleans the old filter and takes the dirt throughout the engine.


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