I was bleeding my coolant system after changing my water pump and hoses, had the expansion tank cap off and the bleeder screw out. Added coolant to expansion tank as coolant and bubbles bled out of bleeder hole, heater on max, engine at 2000 rpm. All was going well, lots of air escaping when suddenly coolant started coming out of the expansion filler hole and the bleeder hole. Don't know what the problem is...thermostat?
Any help would be greatly appreciated!