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like the thread title says, the oil pressure light only comes on at idle. i have read that this is caused by the bearings. is this the case? or are there other possible causes?
i would assume if the oil pump was bad then pressure would be low at all times?
Could be the oil pump it is a gear driven unit, very old school, it will turn slower at low RPM. They have been known to crack which will reduce overall pressure.
Oil pump could be on its way out. Could also be excessive bearing clearance.
I had a supercharged LS motor that had that issue on 5w30 switched to 10w40. This was at 70k miles. I sold the car at 130k miles and motor was still fine.
Even with the oil pump in good condition, pressure can drop if its pressure regulator (picture) is stuck open because of crude build-up, broken spring, worn parts, or lazy electrical sensor...
Could also be caused by a walked cam bearing. We need to see the oil pressure hot and cold, also at idle and 2000 rpm. How long have you had it, how long has oil light been on? You can check bearings and by dropping the pan, takes about a half an hour to get it off. If it is not the bearings, you can then think about pulling the front cover oil pump - figure 2 more hours for that.
I agree with a walked cam bearing. I have seen some worn cam, crank and rod bearing and no oil light. If it is on only during idle or low RPM it points to cam bearing. This was the case in my 04 when I pulled it apart. Oil pump good, crank and rod bearings showing a little wear and one walked cam bearing. If you don't want to pull the pan it is also easy to diagnose by pulling off the intake, injectors and valley pan, it opens up the top of the motor and you can easily see all of the cam, cam bearings/races. Best of luck!