Question about 1999 GMC Denali

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Low oil pressure

My 1999 denali has low oil pressure when it gets warmed up it and is a running speed going down the highway the oil pressure is only at 22.

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Did you check this with a mechanical guage,what weight oil are you using,does this car have an oil cooler. get back to me, also what engine and milage Thanks Ray

Posted on Nov 12, 2009

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You may have a bad sensor or the oil is in need of service. Only hands on diagnosing will find an answer

Posted on Nov 12, 2009

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Posted on Jan 02, 2017

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Low oil would not show up on the engine computer, but low oil pressure would. If the oil light did not come on before the engine stopped, its possible you toasted the engine.

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Have you tried to replace the oil pressure sensor - it helps regulate your oil pressure in your vehicle. Not an expensive part but they do go out from time to time.

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I have a 2000 lsi sedan 4cyl runs excellent good compression mileage has got considerably worse down to 22 hwy any ideas

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Oil pressure drops with reduced rpm,after about 10 min of driving

OIl will get thinner as it warms up and since the oil pump speed is directly affected by the engine RPM's, a drop in pressure after the car reaches operating temp is normal. The question is what are the pressure readings "cold" and "hot" and are they within acceptable specs.

At idle the oil pump is not spinning that fast. When your cruising down the highway, the engine is turning a lot faster and therefore the pump is spinning faster. The faster the pump spins, the more pressure it will make to a point.

Since pressure and flow can be affected by the "weight" of the oil and the operating temperature of the engine, It's hard to make a diagnosis on the internet. You should take it to a repair facility that you trust and have them hook up a mecahnical oil pressure gauge and monitor the pressures cold and hot at idle and crusing RPM's. Then compare the readings with what Jeep says is acceptable.

Low oil pressures can be an indication of among other things worn bearings.

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Low oil pressure, confirmed oil level is good. so before going all the way to changing oil pump, could it be the oil sending unit?

when the engine is cold the oil pressure should read 60 psi
when the engine warms up at operating temp. it should read 12-16 psi while running at speeds 40+ it should read about 38-42 psi.
it it reads all that its not you sending unit
remember its a GM they use the poorest oil pumps on the market. usually I won't see a pump going out untill over 100K or so. its the same frame as the suberben, yukon, tahoe,denali.
4WD will make the job 3 times harder. If you do have the job done ask for a high volume pump

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It plunges down to zero at times then reads eratic

Your oil becomes too fluid as the engine gets warmer. When the engine rotates slower at stops, the oil pump won't make pressure. At speeds, more oil is pumped and the pressure rises.
Have you recently changed your oil? Or maybe is too old. The real problem would be if you read zero at normal cruising revolutions.

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Oil pressur low

I have just cured my low oil pressure (and leaks) by using a stop a leek additive from e-bay. LUCAS engine oil stop a leak. £14.99($22 approx)
It takes a while too get it in the engine as it is extremely thick, but works very well. It evens stopped the slight noise from the oil pump.

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If its the 3.0 diesel it could be the rail oil pressure sensor starting to pack up .

Jan 21, 2009 | 1999 Isuzu Trooper

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