If the heater core is leaking or stopped up, then this is crucial. It will inhibit the flow of the coolant through the whole cooling system. It would be about the same as a radiator hose, or the radiator itself leaking or being stopped up.
how can i test to see if the heater core is blocked up?
does it take a long period of time to blow heat or no heat at all?
wouldnt know didnt turn the heat on for the test drive. ill have to take a MUCH better look next time i go look at it.
k well we will be trying to help along the way