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My 2008 GXP intermittently shows Service Engine light. Code is due to oil pressure sensor malfunction. I put a gauge in place today and saw 40 psi at startup, which dropped to about 15 psi within a few minutes as the engine warmed. A fairly loud lifter tick showed up when the pressure was low. I took the car for a drive--about 10 miles--and rechecked the gauge. After thorough warmup, oil pressure now shows 35-40 psi at idle.
I thought the gage might be stuck, so I shut the engine down and it drops immediately to zero. Startup still shows 35-40 psi at idle.
Engine has 165,000 miles on it. Oil now in the engine is 5w-30. Filter is AC PF63. Oil consumption is about a quart per 1,200 miles.
Is there an explanation for the oil pressure variation as I described? Why does a hot engine show more oil pressure at idle than when first starting the engine?
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