Oil pressure and knock. clueless

Ok, bought this car about a year ago. We were told that the engine only had about 5000 miles on it. Right after we bought it, we gave it to a friend to do some body work. Now we have it back and I am a little concerned about the oil pressure that's showing (I also dont know what the normal oil pressure readings are so bear with me); Ok, when its cold, it idles at about 40 psi. Then when it warms to about 190, it idles like at 5-10 psi. Then we can be cruising like at 40mph at it'll show about 20-30 psi when warm. So basically, as it warms up, oil pressure will slowly drop. I know this is normal, but i dont know if it should be dropping this much. Also, when i start it when cold i hear a knocking noise coming from inside the engine when idle, after about 20 seconds, it'll stop. Basically, im wondering if this type of behavior is normal or not. is it? please and thanks

Yes, that drop in oil pressure when the engine warms up is normal. And oil pressure depends on engine speed, so any speed over 2K RPM will yield a 40 psi if I remember correctly.

Chevy engines "relieve" at 45 PSI if an older smallblock. Later engines carry as much as 70. At a "hot idle", it should be above 15, but "normal" is at least 25.

If the "knock" more resembles a "rumble" than a "clack", it's a main bearing. If it's a "light clack", it COULD be nothing more than a lifter that bleeds down overnite. A "loud" clack would probably be a rod bearing. Since it goes away once it's built oil pressure, it's not a valve guide. They too, can make wierd noises... The engine sitting around a body shop doing "nothing" isn't good. A body shop is a very "hostile" environement for engines, with all the dust that flies around. If the engine was completely covered (more than just closing the hood), that's not an issue.

FWIW

Jim

ok. thanks for the replies. and it runs like at 10psi during idle so im pretty sure i gotta look inside and see whats wrong.

Minimum: 6 psi @1,000 rpms, 18 psi @2,000, 24 psi @ 4,000

well, im definitely in that range. but where'd you get those numbers? just for accuracy and curiosity purposes

Well, hold that thought, what year car and engine do you have?
Those figures are off an LT1 spec sheet.

It's a 1970 camaro with a 350. Also, when the car is warm and in park or neutral, it'll idle like at 15-20. But when I put it in gear it drops to like 10 psi.