HELLO, I HAVE A 2007 MINI COOPER S WITH 55,000 ORIGINAL MILES.

This vehicle continues to overheat and build up pressure in the expansion tank and causes the expansion tanks cap to explode.
I have replaced the thermostat, and I still have the same issue. I've taken the car to a shop, and the mechanic is telling me that he thinks there is a blown head gasket. There is no white smoke coming out of the exhaust or black smoke, checked for water in the oil none. The mechanic then drained all of the radiator fluid and filled the car with something called blue devil gasket repair. After this repair, the vehicle was still doing the same thing, any suggestions as to what the problem or fix might be?

 

Have you/your mechanic checked the water pump? The water pump on these cars is not turned directly by a belt.




The water pump (purple arrow) is driven by an intermediate friction wheel (blue) that is in contact with the accessory belt. The rubber around the water pump pulley can start to deteriorate and come off leaving the intermediate friction wheel unable to turn it. The friction wheel can also be seized which can also be caused by a leaking water pump.

And if you want my honest opinion, your mechanic is a hack. If he's using radiator stop leak to fix a head gasket issue he's an idiot. Bring it to someone who actually knows what they are doing. He may have actually just screwed up your cooling system even worse.