Heater Hose Routing Re-Visit

[neteng01]

Hi All,

I know this is an old thread, but I have an interesting question that maybe someone can help me with. I purchased a new to me 1972 C10 a couple months ago. The PO changed out the original motor with a 1989 Trans Am 2-port 350 motor with a serpentine belt. He told me that the water pump rotates backwards on these motors?? no idea on my side. The problem is that I cant get my heater to work for the life of me. I have a new core, blend door works fine, all new vacuum lines, all new heater hoses, cleaned out heater box so no obstructions. Blower works on all speeds, all new ducting under the dash, and just about everything else is working.

My question is this, the PO ran the heater hoses with the 3/4 hose from the top port of the heater core to the radiator, and the 5/8 hose from the bottom port of the heater core to the water pump. He has several temp sensors in the intake for electric fans and temp gauge. The hoses seem to get hot, slowly, but my heater always blows cool, even with all doors in proper positions. The only thing I have not changed is the thermostat since the motor seems to run at normal temps.

I am at my last nerve here and cannot seem to figure what the issue is. I know that modded motors can cause some challenges, however, he swears that it all worked last time he tried and that I must have something clogged or wrong. Could the water pump connection be the issue here?

Any help or opinions would be greatly appreciated. My C20 is warm as ever but I am feeding as it should via manifold and radiator connections.