I have a 2008 mini clubman cooper engine code N12B16A. A couple of days ago the temp light came on amber just as I arrived home, the next day it came on amber and then red and I took it straight to the garage I normally use where they identified oil in the coolant expansion tank that has exploded out of the cap. But there's no sign of water or coolant in the oil which I thought is usually the case with HG failure, also no smoke from the exhaust etc. They're scratching their heads as to where the fault originates, can anyone help? I suggested oil cooler/heat exchanger gasket problem after looking on line but they're saying this engine desn't have one.