I own a 2009 Mini Cooper S. There is about 60k miles on her and the coolant started to leak a day ago. I started checking to see where the leak was coming from and it looks to be in the area of the thermostat housing (which I found is a common problem). However, today I noticed that when I pushed the accelerator, white smoke was coming out of the exhaust with visible fluid as well. Could a crack in the thermostat housing cause this smoke or could this coolant leak be from something else? Like a cylinder head?

 

Sounds like a head gasket. Does the oil look normal? Either way, a compression/leak down test would be a good idea..

 

Ok thank you. From what I can tell the oil looks normal. And can you usually see an external leak if it is a head gasket issue?

 

Normally, no. If the head gasket, the leak is usually between a coolant pathway and a cylinder. Am basing this on your comment about white smoke and liquid exiting the exhaust. If you're lucky, it's just gasoline that has a high amount of water in it.

First step is to determine that you don't have an external leak, which would be the better situation. In that case, the most likely culprit is the thermostat housing..

 

Oh ok, sorry I forgot to mention that there was a visible external leak. The smoke didn't appear until today when I was trying to figure out where the leak was coming from. Right now I am working on the thermostat housing though. Are there any signs I should look out for when I get to it?

 

If the smoke out the tailpipe doesn't smell like coolant, it isn't coolant. It could simply be condensation; water is one of the products of the combustion of gasoline.