If you put a larger pulley on it the pump will turn slower. Not a good idea on an engine thats has a tendency to run on the hot side. I put a V8 pulley on my new 6 cylinder engine for safetys' sake and no problems. Here its get sometimes in the tripple digits for two weeks or more. Need all the cooling I can get. Make sure there is no water in the oil. Anything coming out of the tail pipe other than just condensation? Check the end of the pipe to see if its wet with antifreeze or gooie. Do you smell antifreeze when it runs or sets for a while? Any steam? Leaking heater core? You can buy a radiator pressure gauge unit from Snap On or the Mac Tool man. Its nice to have one. I have seen small pin holes in hoses that don't leak until you run it then stop when the pressure is gone no more leak. Just my 5 cents worth.