It was bypassing the heater core. I have no idea why but it was. We even pulled the heater hose off the core while it was running and it was dry as a bone with coolant in the system. Leaked like a sieve. It fell apart when we pulled it. We just kept the coolant topped off until we could get it swapped. Had to pull the cap everyday to eyeball it cause you can't see the level through the Tank.