Question about 1999 GMC Suburban

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Oil pressure drops once it gets warm

When the motor is cold oil pressure is at 40psi once it gets to 110 degrees the pressure will botom out if you don't stay on gas and keep rpms at approx 1500 or higher has bad knocking sound when pressure drops

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  • Joseph Lukas May 11, 2010

    Is the cold oil pressue 40 PSI at idle?

    Does the car make the knocking noise only hot?

    How many miles on the car?

    Has the car ever run out of oil?

    Does the knocking noise go away off idle?

    Does the knocking noise sould like a lage block of wood being hit with a hammer?

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  • Master
  • 508 Answers

Sorry to say it sounds like the motor is gone. Higher oil pressure when the oil is cold is normal. But, when the engine gets to operating temp and the pressure bottoms out and the engine knocks you have big problems. If the mileage is very high (150,000) or more your bearings are so worn that the oil can't fill the void between the surfaces and thus the low oil pressure.

Posted on Feb 07, 2009

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Posted on Jan 02, 2017

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