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post #1 of (permalink) Old 10-09-2000, 09:04 PM
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oil pressure up and down

Have 88 GMC 4x4 owned since new, now has 150,000 miles. Oil pressure sometimes 45lbs cold-30lbs hot. Other times 25lbs cold- 5-0lbs hot ! Gauge alert comes on at idle.
Whats going on? This has been happening for 2 months. Changed oil, filter, still no change. Could it be the sending unit? Not sure where it is, unpluged the one by the distributor...no change, aparantly that's not it!?
Anyone have a problem like this before? Would appreciate all responses.
Thank you, Roger B.

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post #2 of (permalink) Old 10-09-2000, 10:50 PM
Drew K1500
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Re: oil pressure up and down

These trucks have some problems with the gauges. My gauge is never consistent. I replaced my oil pump with a high flow and also the Oil sending unit. It didnt do to much. I was told not to worry about it but then again my light never came on either. Try a heavier weight oil next time. I have seen folks put full synthetics in their 150,000 mile engines and wonder why their pressure was so low. I dont know what oil your running but this might help.

post #3 of (permalink) Old 10-10-2000, 02:02 AM
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Re: oil pressure up and down

i have about the opposite problem. mine is always high, but kinda bounces around. i too have been told this is a common problem for our trucks. mine was real low like yours and i had the light coming on so i replaced the sender (underneath, drivers side near exhaust manifold - it looks cone shaped) and after i replaced it now it reads high (45-60) but it runs fine so i dont worry. btw - ive got 160k on an 89

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post #4 of (permalink) Old 10-10-2000, 03:25 PM
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Re: oil pressure up and down

Thanks for the input, will get a sending unit tommorow.
Yes, I did put synthetic in and pressure dropped 20lbs.
Have since went back to conventional oil. Anyway, will see
after the sending unit, also will hook-up mechanical gauge tonight to get actual reading.
Roger B.


post #5 of (permalink) Old 10-10-2000, 09:27 PM
FWP
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Re: oil pressure up and down

Good idea. Never rely on factory instrumentation to tell you the truth. A good old mechanical gage is the best insurance as proof of what's going on. I don't know how many times you hear the same story- my factory gage says this, but it's really something else. Happy troubleshooting.

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post #6 of (permalink) Old 10-11-2000, 06:10 PM
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Re: oil pressure up and down

OK Guys, good news, 32lbs idle- 50lbs for high... Taken with a mechanical gauge... Sending unit was bad, wire was burned from sending unit up 2 inches.
Thanks for the help, don't have to pull motor this year anyway!!
Roger B.

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