so i am doing a ls3 porsche cayman swap.. motor is together and amd working all the accessory stuff now. due to clearance with the firewall i am having to run a remote water pump. I am using a continental (bmw) water pump. my question is about the heater core plumbing.

i was going to use an inline thermostat with bypass on the hot outflow back to radiator line. i plan on using the bypass port to supply the heater core.
my question is.. do i plumb the return from heater core back into the hot out to radiator on the other side of the thermostat or do i run it into the suction side of the pump (line coming back from radiator).

my thought is to run it all on the hot side, outflow on one side ot thermostat the return from heater core on the other. i assume this because doing it the other wat will bypass the radiator with some of the coolant and could have the potential for reduced cooling efficency. my concern is that when the thermostat opens will there be enough pressure differential to flow enought water throught the heater core for cab heat?

 

If you think about it, the heater core is like a second radiator. So if anything, I'd run the return on the line coming back. It's not going to make your radiator less efficient to plumb it that way, and I too would be concerned that once the thermostat opens, pressures will equalize and you won't get proper flow through the heater core.

 

not if you’re not using the heat. Using AC for example will no transfer any of the heat from the water to the air

 

What's easier to heat? A pot of water or a bathtub full? Adding volume to a cooling system can and does assist with temperature regulation. Unless the heater core has a thermostatically controlled valve in the hose lines, water is flowing through it and heat is dissipating away from it, period. In your scenario, the hot air is still there, it's just being diverted away by the HVAC system, and the cold A/C is being pumped into the cabin. I guarantee you the heater core is going to be HOT and transferring heat into the air and the surrounding components. Maybe not efficiently, but it's still occurring.