Questions and Answers
Dropping Oil Pressure
Q. I have an 1985 Pontiac Bonneville with the Buick 3.8, Carbureted, 160,000 miles. This problem has been ongoing for the past two years and I have tried several different things to solve it. First I was driving 60 miles to work, I noticed that after getting off the highway the oil light would flicker at stop lights. I ignored it because I used to have a Chrysler product that did the same thing.
Eventually the light stopped flickering and started staying on. Still at stop lights. I promptly changed the oil and oil sending unit. The light stayed off for a few days and then started coming on again only after warm up and still only at stop lights.
I changed the oil again and replaced the oil pump gears (external oil pump by oil filter). Oil light again stayed off for a few days and started coming on again. Again I changed the oil and did nothing else. The light stayed off for a few days then started coming on again. Also at this point the light started coming on at low speeds and at stops. Always only after warm up of about 10 minutes.
I then broke down and pulled the oil pan hoping to find sludge and a plugged pick up screen. No such luck. There was a small amount of sludge and a minimal amount of floaties stuck in the screen. I removed the pick up and cleaned the pan and pick up with solvent. A few days later the light comes on again. I get upset and ignore the light until the next oil change is due.
Next oil change I replace the electric oil sender with a mechanical pressure gauge. At initial start up I have 45 psi of pressure. Chiltons says I should have 37. I am momentarily happy. After warm up at idle in park the oil pressure drops from 45 psi to 18 psi. I drive the car for 20 minutes and on acceleration the psi doesn't go over 25 or 30 psi and at steady speed 8 to 10 psi. At stop oil pressure hangs around 5 to 7 psi. I am at a loss and have no idea what else it could be. Please help if you can.
David
A. I think the problem is just a worn engine. As an engine gets older normal wear and tear loosens parts and oil leaks out. An engine rebuild is the only cure for this. You can compensate for it to a degree by using a straight 40 weight oil. This will help bring up the oil pressure and buy you more time, but it is not a cure.
If you live in a cold climate, starting it in the morning will be a chore also.
Additional Information provided courtesy of ALLDATA
