As someone who had nothing but overheating problems with my G body, it takes multiple overheatings to cook an Olds V8. I am talking the thin castings, Siamese bore Olds 403. Probably an air pocket as said. Unless you are running A/C, I always eliminate that valve, as they tend to leak. I just buy the 3/4" nipple with hose barb from my hardware store. I really like my 4 blade fixed factory fan. It moves a lot of air and doesn't wear out over time.