I have a 2009 MINI R56 Cooper S. In 2014 a mini dealership replaced the Thermostat Housing. Six months ago I replaced the water pump and three weeks ago I replaced the water pipe. Now I have another coolant leak. The car recently overheated because of not having coolant in the reservoir tank. The coolant levels are down constantly. I looked under the car and there is no leak when the engine is cold. It leaks only when the engine is fully warm. From under the car It looks like the water is coming down from what I think it is the AC drain hose/tube under the passenger seat. However, if I understand correctly, water should not come from the hose/tube if the AC is off. Anyone knows where this leak can be coming from?

Thanks.

 

Water will continue to drain from the AC for a while after it is shut off.

 

Thank you for your quick response. I totally understand. However, if you do not turn the AC on at all and after the engine is fully warm you see water coming down by the AC drain hose/tube, that is not normal correct? That is exactly what happened. I am just trying to see if someone has experienced the same or a similar situation. Any info would be greatly appreciated.

Thanks.

 

Today, I filled the reservoir tank all the way to the top and I drove to a friend's house (about 20 miles away). When I arrived, I looked under the car and the car was leaking water by the Exhaust Flex Pipe (front pipe). So based on the location of the leak, it was leaking from the back of the engine. Almost an hour later, we lifted the car, placed two jack stands, checked under the car and there was no leak. I started the car to make sure that the engine was fully warm, I went under the car again and no leak. So I removed the intake air housing to see if I could see any signs of a leak by the thermostat housing and/or water pipe and I couldn't see anything. If there is a leak, it should always leak. This does not make any sense. For the record, the car overheated at least once when the water pipe broke down. Does anyone have an idea of what to do?
Thanks.

 

borrow a coolant system pressure tester and let it sit overnight and see where the pressure leaks out. Keep us posted.

 

I will conduct a pressure test probably next weekend. By the way, before the water pipe broke, I took the car to a mechanic that owed me a favor and we performed a pressure test. We couldn't see any leaks. In theory, this does not mean that if I perform a pressure test now a leak will not be discovered. I just wanted to mention this just in case. Today, someone told me that it could be the heater core that is leaking. Could this be possible? Any ideas?

Thanks.

 

I have had heater core leaks in a Tahoe and an Audi, but not in my mini yet. A slow leak can be difficult to find. I would replace the coolant reservoir cap as safe measure. I would also drain the system complete and measure how much you fill by. Use tre bleeder screw on the thermostat housing during prep and get ALL the air out.
if all else fails, get a painters tarp and park on it each night. You will find the drips eventually.

 

I think you have another failed thermostat housing. Coolant drips from a crack onto the transmission and evaporates, never reaching the ground. Not an unusual failure.