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Sunny

Fan blowing cold air when stationary - but ok when driving along

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Hi all,

My E39 doesn't blow hot air when I'm stationary but seems to be ok if I'm driving along.

The dial is set to ''heat', and the vent dial is 3 red dots for heat also.

Does anyone know what the issue could be please?

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Or a weak water pump? Air lock

YNP

Content provided by this user should not be considered correct due to the fact he's a raving fruitloop.

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At idle speed, the engine water pump isn't able to provide much flow through the cabin heater core. So BMW fitted an electric auxillary water pump that provides additional flow of hot coolant to the heater core to ensure cabin heat is always available. If the aux pump fails one would expect loss of cabin heat when the engine is idling while stopped with good heat during driving at increased RPM.

 

Depending on year and optional heating (latent or Wabaso) the auxillary pump is located

1) on the left side bottom of the fan shroud

2) under the heater control valve

3) in front LH wheel well behind plastic cover (EDIT: rear side near door, not front near headlight)

 

The auxillary pump is turned on whenever the HVAC panel is calling for cabin heat. To check its function:

1) turn the ignition key to run, but don't start the engine (quiet & no moving parts during check)

2) set the HVAC panel to a high temperature, i.e. demand cabin heat so aux pump should be turned to on/run

3) listen in the engine bay for a quite hum or better yet touch the pump to feel for slight vibration.

 

Another, less conclusive check would be to increase engine RPM while stopped & see if cabin heat returns.

 

BTW, air in the coolant system more often results in engine overheating &/or lack of cabin heating at all engine speeds, not at idle only. Or so people report, I've not suffered the problem - at least not yet.

 

Regards

RDL

Edited by rdl

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Very useful post RDL, thanks. I have very similar symptoms to OP.

Is the auxiliary pump item 2 here?

http://www.realoem.com/bmw/showparts.do?model=DS42&mospid=47556&btnr=64_0929&hg=64&fg=18

I find I get no heat below 2k revs,plenty heat above 2k revs. So I get heat if gearbox is in sports mode!

Sent from my iPhone 7 using Tapatalk

Edited by MJM

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Sunny, any feedback on your issue?

Edited by MJM

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...

Is the auxiliary pump item 2 here?

http://www.realoem.com/bmw/showparts.do?model=DS42&mospid=47556&btnr=64_0929&hg=64&fg=18

I find I get no heat below 2k revs,plenty heat above 2k revs. So I get heat if gearbox is in sports mode!

...

Yes pt #2 is the auxillary pump. The physical pump has a cylindrical shape rather than pancake as shown.

 

Regards

RDL

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Thanks. Will check the three locations you suggest this weekend and see if its running. Cheers for the help. :-)

Sent from my iPhone 7 using Tapatalk

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Had a root around the engine bay, checked fluid levels and found my coolant was low. :rolleyes: Topped up and my problem has gone. Woohoo! Hope the OP has similar success.

Sent from my iPhone 7 using Tapatalk

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Had a root around the engine bay, checked fluid levels and found my coolant was low. :rolleyes: Topped up and my problem has gone. Woohoo! Hope the OP has similar success. Sent from my iPhone 7 using Tapatalk

 

Ohhh... good idea to find where that went!

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