I think that you have it right in the second part - there is still a total amount of heat that will be transfered to the front of the car. You would save a little bit of surface area of warm pipes that radiate heat, but not much. Additionally, the radiator pipes are much larger in diameter than the heater pipes. I don't think it would make a noticeable difference in sill temperatures if you bypassed at the engine instead of up front. But you'd have to actually do it and measure it (or do an awful lot of calculations) to know for sure.JnC said:I may be making a bad assumption, but if the water in the heater core loop is as hot as the water in the radiator loop, wouldn't you be cutting the amount of hoses running hot water by half?
Or is the amount of heat generated by the engine now fully transferred to the radiator loop, and the net dissipation from hose to chassis hardly changed?