Just because it wasn't mentioned, I figured I would seeing as you are in The Great White North according to your header.
Did you flush the system with water before filling it up? I ask because this throws the 'premix' antifreeze percent 'way' off. When you water flush, water is left in the block and heater so you need to add the correct amount of pure antifreeze first, then top it up with water when refilling.
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail >