Oil weight - Psi change?

GoodysGotaCuda said

Anyone give an estimation on what different weight oils do for pressures? I'm not looking to change, just for my own knowledge.

I currently have 15w-40
75psi - cold idle/cruise
35psi - hot idle
65psi - hot cruise

10w-30?
10w-40?
5w-20?

Thanks :headbang:

Click to expand...

I'd be guessing Goody but 10-30 down 5 psi, 10-40 no change, 5-20 10 psi.
I used to run 10-40 and switched to 10-30 (a little cooler up here) and didn't see a difference but then the engine is recently rebuilt and all the bearing clearances are all still tight. On an engine with a lot of miles you could see a bigger difference as the main and rod bearing clearances will have opened up.

Terry