i had over heating on mine.. replaced the thermostat problem solved.. also recently had a loss of coolant this happened to be the o ring at the bottom of the epxansion tank, i removed the radiator and pulled the expansion tank out and give it all a good clean and flush through replaced the original coolant tank.. with original o rings and they have sealed now... not really had much problem with bleeding my coolant just topped up the coolant and give the hoses a good squeeze to get the air out also make sure the heater fan is switched on in the car and on hot...while bleeding
you will probably find that if the thermostat is bypassed i.e. removed the inside, that the car should take ages to warm up and will be using more fuel as probably in open loop mode a lot longer replace the thermostat for a new one... its there for a reason...to get the car to warm up quick....
hope you get it sorted...