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Matt, Mechanical Engineer
Category: BMW
Satisfied Customers: 22761
Experience:  BEng hons Mech engineering, in auto industry 22 years
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The heater on my 525i just stopped working and now the temperature

Customer Question

The heater on my 525i just stopped working and now the temperature gauge keeps showing the car is overheating - what would be the most likely cause please?
Submitted: 3 years ago.
Category: BMW
Expert:  Matt replied 3 years ago.


Very first thing to do is ensure the coolant level is up to the mark and if low top it up with the correct antifreeze or pre-mixed coolant as stated in the owners manual

I'd then check that the engine is getting up to temperature, if its not then its likely the thermostat needs changing.

If this is OK have a feel of the two coolant pipes that pass into the car through the engine bay bulkhead, both should be warm with a warm engine. If they're not then its likely the heater matrix is blocked and you should do a reverse flush on the cooling system to try and clean it out. This is done by removing the top hose from the radiator and placing a garden hose into the engine water outlet, and then run the hose until you get clean water coming out of the radiator.

If this doesn't help this only leaves checking out the motor / cable that move the air mixing flap that allows the hot air from the matrix to enter the car air system.

This flap is controlled by the temperature knob / dial etc and I think is controlled with a small motor for your car so the thing to do is first get access to the back of the control knob and measure the voltages is present there, then trace the wiring back into the dash from the control to locate the motor.

It’s worth first checking the fuses for the fan / control circuit

I'd recommend first removing the glovebox ( undo lower edge hinges from dash) to gain access to the dashboard inner and also allow you to shine a torch to the back of the central console so you can start tracing the wire back and see how things are put together

Customer: replied 3 years ago.

Thanks Matt


That is pretty detailed advice. Realistically I don't have the time or the aptitude for this type of work - I will have to take it to a garage.


The problem is that - having only a very rudimentary understanding of car mechanics - I don't know who to trust.


My first call today was to the place I bought the car and almost the first thing the guy said was 'sounds like cylinder head gasket'.


I have checked the coolant level and that is full. The car runs smoothly. Is it possible that the fault could be something as major as a cylinder head gasket? I notice that you did not include this in your response.


Kind Regards




Expert:  Matt replied 3 years ago.
Hello Mitchell

head gasket is a possibility but thats a bit doom and gloom when there are aother reasons which are cheaper to fix

if you can tell me where you are in the country I'll try and reccomend a garage
Customer: replied 3 years ago.

Hi Matt, Thanks


I'm in Blackpool, Lancs - famous for it's tower, fish n chips, Blackpool Rock and kiss-me-quick hats


Thanks again




Expert:  Matt replied 3 years ago.
Hello Mitchell

try this firm

only thing to check before getting any work done is what labour rate you'll be charged as this can be a bit variable and shouldn't be main dealer ( £100/ hr+ ) levels
Customer: replied 3 years ago.

Thanks - i'll give them a call


Expert:  Matt replied 3 years ago.
No problem hopefully they can help

feel free to pass on my advice and if you need more help just get back to me on this post