My 350 SBC does not have a bypass hose, instead it goes to the heater core. I have seen 2 scenarios on a SBC, a bypass line and no bybass line. My questin is, if I don't have a bypass line can I shut off the water to the heater? The heater core in my F100 is new and has been problem free, at least until I shut off one side of the water flow. I installed a vacuum operated valve off of a Buick to shut off the heat in the summer. Soon after this, my core developed a leak. The shutoff valve never completely shut off the water to the core, this was evident by a little heat. Is it possible that without a bypass line the heater is the bypass and the high pressure caused a leak, or is it just a coincidence that the leak started? For now I'm going to disconnect the heater core and install a bypass on the motor. This will give me time to fix my leak but sooner or later I'll have to put it back in.

hi, i dont know if this info will help but i run two temp gauges one in the manifold ,one inthe right head . i realised that when heater is on and heater valve is open that head tenp and manifold temp equalize .so i plan to route a bypass when heater is off.i found it only because of the two gauges there was as much as 10,20 degree c differance without bypass or heater.

loop it...remove one heater hose completely and hook the heater end of the other hose to the block connection