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Steve, BMW Expert
Category: BMW
Satisfied Customers: 25397
Experience:  BMW Expert
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When heater is on full the air keeps blowing hot and cold,header

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When heater is on full the air keeps blowing hot and cold,header tank is holding water on full,after 10 - 15 miles the engine fan cuts in and get a yellow thermometer sign comes up on the dash display and after a while goes red
What is the last 7 digits of the vin?
Customer: replied 3 years ago.


I will provide an honest answer. I trust this will be appreciated. Please remember that a low rating PUNISHES me for being honest and that I receive nothing for my time until a positive rating is clicked.

the most likely cause of this issue on your car is a failed water pump

this can easily be confirmed by having the faults read from the car's computer.

another possibly cause would be a faulty thermostat, faulty temp sensor or air in the cooling system, but more than likely the water pump is the issue. If you are replacing the water pump, be sure to replace the thermostat at the same time.

Please let me know if you have further questions. Please do not forget to click a positive rating as this is the only way I receive credit for my answer, thank you. Best wishes with your vehicle

if there are no additional questions please kindly CLICK ON a positive rating. thank you


I can see that you have rated my answer as "bad"

this PUNISHES me for answering your question and trying to help

can you pleaes clarify what part of your question was not answered?

Customer: replied 3 years ago.

Dear Mr Expert

My apologies I did not intend to give you a bad mark ,I pressed a button and it sent whatever was on the screen oops !

I have fitted a new thermostat and the problem seemed to be solved but after 25 miles the overheat light came on again,I know BMW's are notorious for getting rid of airlocks do you think this could be my problem?

As I stated in my original answer I think the water pump is the most likely cause.
Air in the cooling system can also cause an over heat, so this is also possible.
As the question has been answered, please kindly change your rating to OK or higher. Thank you in advance.
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