On a SBC is the fitting at the top of the water pump supposed to be an "in" or "out"? Because of my TPI setup, I ran the heater core "in" line from the water pump. The other hose from the core goes straight to the radiator. When driving it the other day in 80* weather, I decided to check heater operation. It wasn't very warm. I checked it on vent setting, and it was colder than normal. I've been having problems with the overflow as well...the radiator would be two inches low, but it never seemed to pull any from the overflow...I'd keep adding to the radiator, pop the cap after running it and letting it cool, and the radiator was low again. One thing I noticed while doing this, is that when the engine is running, no coolant is coming out of the heater core line. Sounds to me like the water pump fitting is an "in", but I've never dealt with it before. I plan on running it from the intake like it should be (well, minus the 180* formed heater hose) but it looks like I will have to get a nipple with smaller pipe threads that what was used on the old intake and in the water pump now. The threads in the intake are the same as the "small" holes in SBC heads (as opposed to the 3/4"? holes in some SBC heads) used for the temp sensor for the gauge. Anyone run into the different thread diameter nipple problem either? I was under the impression before that all were the same size, perhaps it's the newer ones that went smaller. Just wondering if anyone knows for sure that the water pump fitting is wrong to use. With no coolant flow it's pretty obvious I guess. My dad told me his earlier short water pump has another fitting on the passenger side of the water pump, my later one does not.