Dayco supplies many nice tap valves (on/off/in between). Tap into line from engine to rad (fluid prior to entering top of rad).
Wrong.
To supply a heater core.High temp, high pressure coolant is sent to the heater and coolant returns to lowest pressure point of the cooling system .
Tap in the supply in the engine side of the thermostat. Return heater core line to the water pump inlet.
...except liquid cooled engines designed with reverse coolant flow.
Not a whole lot of those reverse cooled engines in standard mid priced production vehicles and equipment. It is a superior cooling system however. iirc Chev ran off a batch of performance reverse cooled V8's in the mid 90's ?