I have a 1993 Chevy C1500, and about 3 weeks ago I started noticing that whenever it gets to temp I start hearing a knocking coming from the valves, and I lose almost all oil pressure. I also lose a lot of power. What could be causing this? Am I looking at a full on engine rebuild? PLEASE HELP!
That doesn’t sound good.
Have someone install and oil pressure gauge in place of the oil pressure sending unit. Start the engine and let it idle until it starts to heat up and watch what the oil pressure reads. I bet it shows zero.
Ok, we’ve done that. And when it first starts it does show pressure.
How many miles on the engine, what is the oil change history of it, and what weight of oil are you using? Also, has the engine ever been run low on oil or overheated?
It sounds like you have worn engine bearings which are no longer holding pressure when the oil heats up and thins out. This is common with high mileage/neglected engines. You may be able to get some more life from the engine by going to a thicker oil–eg. if you’re using 5w30, use 10w40.
Another possibility is a worn oil pump, or a defective/clogged filter, but these are unlikely unless the engine was great one day, then the problem developed the next day.