My 06 cooper overheats when it is being driven, but not when it's sitting at idle. Also the heater does not blow hot air. I can hear the "door' opening in the dashboard when i turn the heater on, but it still blows cool air.

I just replaced the motor with a used motor, everything is working great except this issue. I used the thermostat off my old motor b/c it was replaced along with my radiator fan about 10k miles ago.

Any ideas?

 

Air in system, bad water pump? These cars are hard to bleed properly. There is a second vent screw down hidden on the pass side of engine. If you are lucky, that is what you need to do.

 

I think you mean on the driver's side? It's down near the thermostat housing.

And yeah, sounds like air in the system to me....

 

Thank you, I will give that bleed screw a try.

 

I would check the thermostat - is it installed correctly? Sounds like something is wrong in opening the entire system and would explain why the heater is not getting hot.

 

I had a leak in my antifreeze in my 2005 R50 and brought it in to my mechanic. He fixed the problem but when i was driving home i realized that i had no heat... So i turned around right away. All he needed to do was fill up the antifreeze and open and close the liitle bleed screw(left side of the engine/ passenger side) and let the air out. The antifreeze resevoir was already full, so what he needed to fill up was the little thermostat cap just to the right of the engine(driver's side). Once that was full the heat started working. He said it was because there was no circulation in the engine.... whatever that means.
Just verify that you've got enough antifreeze in there.

 

The problem is related to the water coolant.

How is the water level? First thoughts is that you have a water leak somewhere and theres a low level of water in the system. I had this exact problem on my old car and it was the water pump that had gone and it was losing water.