I have a 1999 Pontiac Bonneville, 3800 6cyl. I started my car one day and I heard a loud knocking in the engine for about 30 seconds and then it stopped. I noticed my oil gauge needle is usually slightly below the center which is numbered 40 and when I step on the gas or drive the needle moves just past the 40 mark (past the center of the gauge) The engine knocked again in the morning but not as loud or as long. I no longer hear any knocking when I start the car but I noticed my oil gauge needle does go up to almost 40 but as I continue to drive for a while it drops quite a ways down and no longer reaches the 40 mark on the oil gauge. It is not in the red zoned area on the gauge but I think if I drive a long distance it will continue to drop down lower. I have added more oil then is needed my engine now has about 6-1/2 quarts. What could be the problem? Is my oil pump done for?
When engines get old and they wear, the tolerances open up and the oil can flow through easier, causing the oil pressure to be reduced, the same thing happens when the oil gets hot, it gets thinner and it flows easier. This does not mean the engine is shot, by any means. It just means that you might consider a higher viscosity oil at the next oil change. Consider it within normal parameters.