The rad wieghed a TON when I removed it. doesn't look like it had too much mud in it but I guess it has a lot of calcium build up. Mabye the po used regular water to mix with the coolant. Anyways, runs fine now but I have to design a system to protect the rad next time I have to run the brown stuff.

 

Lesson learned: If heater ON brings overheating down to normal, its the friggin radiator. Energy In = Energy Out minus any losses.