Heater cores are no more difficult to flush than a radiator. Heater cores are just little radiators. Even with the mixing of coolants power flushing the entire coolant systems - with the thermostat removed - should take care of it. I expect it's going to take a while before the system runs clean. It was suggested to me to periodically reverse the flow. I don't know how much good that does as I've never had a coolant system in this bad a shape.

The bad news - depending on how long it was run with the two coolants expect to be replacing a water pump in the near future. Replacing ALL the coolant hoses - everything in the cooling system with rubber (cap, too) - is just a given. <img src="/forums/images/graemlins/frown.gif" alt="" />

If you don't have a lake of coolant on the passenger side floorboard the rushing noise from the dash is air being flushed through the system. At this point you have bigger problems to deal with than bleeding the cooling system.

Edward