Why does my oil pressure drop down to 0?

Tiny
CHEVY350SB
  • MEMBER
  • 1993 GMC SIERRA
I have a 1993 gmc sierra z71 with a 5.7L engine. Engine was replaced with a used one. My question is that "Why does my oil pressure drop down to 0 KPA after it has been running for a few minutes, but pressure is normal when the engine is cold? I replaced the oil pressure switch and my engine was running fine for about a week, now when the engine heats up the gauge on the dash drops to 0 kpa.
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Monday, October 26th, 2009 AT 6:59 PM

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Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,014 POSTS
Hi,

Several different things can cause a low oil pressure issue. If the oil pressure is truly dropping to 0 PSI, you will likely hear a knocking or ticking from the engine for a short time. Ultimately, the sounds will get worse until there is engine failure and it shuts down.

If you don't hear any noise, then it is likely a wiring issue and not the oil pressure switch you replaced.

Here is where I would start. To determine if there is actually no pressure, go to a parts store and borrow a mechanical oil pressure gauge. Then, remove the new electric pressure sensor you installed and screw in the mechanical gauge. Start the engine and watch the gauge. If it doesn't drop to 0, then we know it's a wiring issue.

First, confirm the connector is not corroded or damaged. Then, trace the wire to see if there is any indication of damage. If nothing is seen, have a helper sit in the vehicle and watch the gauge while you wiggle the wire around to see if there is an internal break.

Also, I found a technical service bulletin related to low pressure warm. Take a look through it as well. It's attached below. (Pic 1)

On the other hand, if the mechanical pressure gauge indicates 0 psi, then there are likely internal issues such as worn main bearings, a possible plugged oil pick-up tube, or even a bad oil pump. I have even seen a plugged oil filter cause such issues.

I hope this helps. Let me know if you have other questions.

Take care,

Joe
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Thursday, September 23rd, 2021 AT 7:40 PM

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