No heat - 328SE

The electronics all seems OK in the heater control unit of my E36 series 1996 BMW 328 SE, and the fan works OK, but I'm getting no heat at all. What is the most likely cause please?

--
Terry, East Grinstead, UK

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Terry Pinnell wrote:

Has it got enough water in the cooling system?
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Doki wrote:

Should have worded that differently - could appear to be enough water at the header tank but air still remaining in the heater matrix. Has it had a coolant change recently?
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happily, sounding much like they were saying:

No experience on this with BMWs, but it's bringing back vivid memories of the XM... Thermostatic climate control in it?
My money's on the hot/cold flap motor not doing so, either because the motor's sulking or because the ECU's sulking. Either way, you're going to need to try to read fault codes from it... The only alternative is swapping bits out, which is probably going to have you spending a lot of time in the footwell playing gynaecologist with the dashboard.
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Or even just the aircon pressure's too low.
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Adrian wrote:

In fact, it might not even play if you do swap bits *without* reading/clearing the codes.
I'll bet Adrian's right though. The flap motors in VAG cars stick sometimes and do this. You can sometimes reset them with diag software.
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Is the valve opening? I think in this unit there is a stepper motor that opens and closes the valve based on the internal temperature. If the valve is physically opening and closing and you have no heat, either the cooling system is clogged or it's not heating up properly because the thermostat is stuck open. --scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

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snipped-for-privacy@panix.com (Scott Dorsey) wrote:

Thanks all. Will get on the case in the morning. Is the 'valve' ('flap') visible, so that I can as a first step check if it is indeed opening/closing? If so, where is it please?
--
Terry, East Grinstead, UK

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You're going to need the Haynes. I _think_ on the US version of that car you can see the linkage on the lefthand seat by removing the cover under the steering wheel, but I am not sure what has to come off on the UK one. --scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

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snipped-for-privacy@panix.com (Scott Dorsey) wrote:

Thanks. But I'm hoping that Doki's first suggestion may prove to be the cause. I had to add over a pint to the radiator just now. Don't want to sit in the drive with engine running on this sunny afternoon, so testing will now have to wait a while.
If it does need panels and stuff removing (and replacing!), I think I'll have to get my wallet out and let the local garage do it ;-)
--
Terry, East Grinstead, UK

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Unhappily that doesn't appear to have been the cause. 60 mile run today but no warm air.

Looks like that's next step ;-(
--
Terry, East Grinstead, UK

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A couple of taps with a hammer on that motorised valve restored warmth!
Probably needs replacing (I suppose it's as old as the car - nearly 12 years) but for time being I'll carry a small hammer ;-)
--
Terry, East Grinstead, UK

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If the motor is freezing (physically freezing due to the cold), then a shot of contact cleaner should fix it. They build these motors with a small amount of grease that collects dust and dirt over time, the combination of dirt dust and grease can solidify and cause the motor to stop working. You need a small shot of a lubricant/penetrant to melt the grease and return it to its original viscosity.
WD40 will clean it, but it will dry out and turn to gum, and cause the whole problem all over again. You could shoot a small amount of WD40 to clean the motor out so it works reliably, then give it a shot of contact cleaner to dilute the properties of the WD40 that turn to gum.
If you can remove the motor to your work bench, you should be able to be able to clean it without disassembly.

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Thanks Jeff. I don't feel confident enough to tackle it myself, but when the time comes I'll ask my local garage to first have a crack at cleaning, as I suspect the replacement BMW part will be a silly price.
--
Terry, East Grinstead, UK

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