Hello, I have a 1998 Chevrolet K1500. I noticed what seems to be valve clatter, high oil pressure of 80 on the gauge and about half the radiator antifreeze was gone. the oil does not look milky I just changed it to see if coolant was in it.
The low coolant and the chatter are most likely not related. The low coolant is probably the lower intake manifold gasket...EXTREMELY common. A coolant system pressure test can prove this. As for the clatter, this is most likely a collapsed lifter which is also common for the Chevy.
80 psi is normal for this engine. Once the engine oil gets some age on it, it may come down some. An engine requires 10 psi of oil pressure for every 1,000 rpm.. so 80 is excellent. 0 is bad. My 2006 z71 reads 80 psi all the time....and i am happy about it.