The radiator in our Blazer was cracked for some time ( a month or more) before I had the time and money to replace it. Yesterday I got the new rad and thermostat installed and noticed I have no heat. My theory is from constantly running low on coolant the heater core has become blocked. My question is this: Does the coolant have a way of bypassing the heater core, or is it causing a major blockage in the cooling system overall? It may be a couple of weeks until I can find time to flush the heater core.

 

It can bypass. The primary flow for the heater core is provided through the water pump and discharges into the coolant passage next to the thermostat.

I would try to flush the core. It is possible that it is just air locked.

 

Great, that puts my mind at ease. I'll give the flush a shot as soon as I can.