I cannot tell you how many times I see this mistake working in the automotive field. The engine is knocking away and the owner of the vehicle or the Technician working on the vehicle replaces the engine oil pump without running an oil pressure test on the engine. Or the oil light is on, the Technician checks and verifies that the oil is clean and full and then “assumes” that the oil pump is bad so they go ahead and replace it only to end up with the same exact problem they had to begin with. Well I got news for those folks, 9 times out of 10 the oil pump is not the problem. It is the engine itself. The engine oil pressure is actually dictated by the bearing clearance inside the engine. Lose the bearing clearance (for whatever reason), and you will lose oil pressure. YES.. there are times when the oil pump itself will go bad. However, the oil pump only produces volume.. not pressure. It’s the bearings (clearance) inside the engine that gets the oil pressure up to specs. Please watch this video below to get a good understanding of how oil pressure works. (Note: this is not me in the video)
Checking oil pressure
If the oil light is on or if the engine is knocking away then it is a good idea to check the oil pressure first using an oil pressure gauge before replacing anything just to be sure. There are a few different ways to check oil pressure. The most common way is to use to screw the end of the gauge into the engine block where the oil sending unit threads into the engine block. You will want to get a nice tight fit on there before you start the engine. The oil pressure will fluctuate with engine rpm and the oil pressure will also be greater with a cold engine because of the cold oil. Once the engine warms up, the oil will thin out and the oil pressure will drop a bit. This is normal.
All engines have different oil specs so be sure to look up the oil pressure for your exact engine just to be sure. You can go to alldataDIY to get the oil pressure specifications for your exact vehicle. If you have low oil pressure, it could result in serious engine damage like this chevy malibu with a broken camshaft.