Hi, I've got a 1978 Buick Regal with a 231 cc 3.8liter Buick V6. It appears to have a problem with low oil pressure. The "engine" light would start flickering at idle speed after it had been driving on the highway for more than 10-15 minutes. Also, in recent months I started hearing some noticeable ticking noises soon after starting the car- they usually went away after a bit. An oil pressure test read about 10 psi. The possible causes included bearing wear and worn oil pump, both of which my mechanic deemed too costly to be worth fixing on an old car.
My mechanic recommended I switch to 10W-40 and add STP. This made the light-flickering go away but not the startup ticking/tapping noise. Lately, the motor has started making much louder tapping noises at startup that take much longer to go away. It seems to be connected with cold- it started with the first really cold mornings and seems worse the colder it is. My thought is that the combo of
10W-40 with the superthick, gooey STP has raised the startup viscousity so high that when its cold the oil is so thick that it has trouble circulating properly. I'm thinking of switching to lower viscousity again- 10-30 or 5W-30 without STP.This would of course bring back the idlespeed light flicker problem, but that never caused any noticeable noises, and anyway I dont go out of town much in the winter. Does this seem like a good idea?
Also, is the oil pump really very costly to replace on this particular model? My guess is that its the oil pump rather than bearings, anyway, as the engine has only 130K miles, sounds nice when warmed up, and has to my knowledge always been well-maintained.