Been having every coolant issue conceivable with this Mini, replaced everything except for the rubber hoses at this point and now coolant is spraying from the top of the tank when it gets heated up.
Parts Replaced: Heater Core(Had a leak), Radiator(cracks from an accident), Thermostat Housing(cracked), Water Pump(leaking), Pipe between housing and water pump(Deteriorated end in the water pump), Overflow Tank and Cap.

Any ideas on what could be causing this?

 

Have you bled the system to get all of the air out of it......

 

Multiple times yes.

 

It's definitely a possibility that air is still trapped in the system

 

Leave the bleeder screw open for a while until the antifreeze starts coming out..... I let mines get to temp and then open it.

 

Done that a couple of times, did it again 2 days ago ran an entire tank of coolant out of it and onto the ground...no change it still overheats and shoots the fluid out of the cap.

 

If coolant is blowing out the reservoir cap, something else is going on beside having air in the system. Are you sure you have all the hoses connected correctly in and out of the thermostat and radiator?

 

Kind of sounds like there’s a blockage.

 

All connections are correct, did a test, and looks like it is the head gasket...which I replaced 10,000 miles ago after the timing chain broke. About ready to run this car into the river...lol.