Hi Everyone,

I helped a buddy put a replacement (used from salvage yard) R50 engine in an 05 Cooper. This was in the summer, everything wet well and car has run fine since. At the time i did the swap I put a new thermostat in it and purged the coolant system, Purging the system was a pain, but it did get to the point where there was no air coming from the bleed screws.

Fast forward to the winter and we're having some -25 (celcius) days. He calls me up and says that the car has heat in the cabin when idling but not when driving. I just confirmed with him that the engine temp drops when this happens too. So my initial thought is the thermostat is stuck open. I did replace the thermostat with a new one when i put the engine in for him, it was aftermarket but I couldn't find anything indicating they were prone to failure.

Being unfamiliar with these cars i just want to know if there's anything else that could be the problem before i go down this rabbit hole?

 

 

while that operation of things is true the tstat is supposed to open and close to regulate the coolant temp. Once the engine is warm the coolant temp shouldn't drop that much which is why I'm eyeballing the thermostat... but I don't know anything about the in cabin hvac portion on these cars so looking for anything electrical/mechanical that could be the culprit.

 

 

Just a thought: Was the thermostat installed with the spring "inside" the engine block (it should be)? If I'm not mistaken, it can be reversed, therefore would not be functioning properly (closed when cold; open when hot).

 

 

Also check the expansion tank cap. If it doesn't hold pressure the engine may not heat properly.

 

Also, make sure there recirculation button is pressed and actually closing the duct door.
Mini's actually draw a lot of air from the outside, if the recirculation system isn't working properly, air that cold could actually just be negating the heated air, esp if it's not heating up 100%.