Last night while towing my trailer with my tractor on, the block heater popped out of the block and I was leaking antifreeze.

This is the second time that this happened. It did it about a month ago also. I upgraded to the newer high volume water pump about 2 months ago but I never got the dual thermostat crossover. I am wondering if this is causing too much pressure in the block and causing this block heater to pop out. When the block heater pops out, it doesn't appear to have anything wrong with it. I am not getting any excessive pressure in the top radiator hose when I first start it and it uses no coolant at all as long as the block heater stays in.

What do you guys think?