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Discussion Starter · #1 ·
Hi all. New to site, and was hoping to get a little help.

My E46 heaters have a mind of their own & at the moment the heaters will NOT give hot air but will blow cold air even if its set to 32c and 3-dot red. The heaters will simply not warm up if left in idle at optimum temperature. They'll only warm up once I'm driving and only after maybe revving past 2rpm... but at traffic lights etc they cool down again instantly.

It doesn't happen if I'm making long distance journeys, like motorway driving. After a journey like that, they'll stay hot for as long as I need them to.

Any help or advice would be much appreciated, thanks.
 

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Sounds like it could be related to the FSR/hedgehog (final stage resistor) or thermostat. Someone on here will know, however.
 

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Does your outside temp display correctly on the dash? Not sure if the EU 320 had that.
If not it could be the Ambient Temp sensor under the front bumper. If the heater thinks it 60C outside it wouldn't send much coolant to the heater core, just bring in outside air.

The US E46s have a display available in the dash that will show your actual coolant temp, maybe yours does too. Search here for Easter Eggs and look through that thread.
If it isn't getting up to about 100C after a 20 minute drive, you may have a failed thermostat, stuck open.
This may or may not give a Check Engine light.

It could also be your water valve. It controls the flow of coolant into the heater core.

Another possibility is your water pump isn't circulating enough water, this would show as cooler air out of the heater at idle and better at higher rpms, but a failed thermostat could show similar symptoms.

If the blower motor changes speeds and blows air out of the vents it probably isn't the FSR, it will often give a slow fan speed when the indicator shows a higher speed.
 

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// Quandt AG (Retired) //
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Does your outside temp display correctly on the dash? Not sure if the EU 320 had that.

It could also be your water valve. It controls the flow of coolant into the heater core.
That's my guess. I had a similar problem on my 325xi. The heater control valve is likely the most overlooked component in any E46 Coolant System Overhaul even though it is relatively simple to change. I removed three from four e46's and they were all in bad shape. Changing them provided more consistent heating and better cooling since it controls the water flow to the heater coil.

Item number 2 in the diagram. It is attached with three rubber mounts on the side of the driver side strut housing (behind & below the air box) on left hand drive vehicles.

 

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the erratic speeds sounds like your FSU.as per the heating,start with the basics. check the coolant level, top it off if needed and also try bleeding the system,
 

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Discussion Starter · #7 ·
Hey guys, thank you every so much for all your responses. I'm going to look into all that over the weekend and see what happens.

Iv checked coolant and bled the system, that didn't help. outside temp on showing correct on trip computer and the car temp needle is perfect as well.

I don't know if this makes any difference, but ever since I bought the car, when putting on the heaters, its always made a weird noise. Its almost as though it struggles and has asthma, heaters sound like their blowing out on/and/off very quickly but then after a short while the noise is a little more consistent like you would expect it to be. Would that mean anything?

Thanks again for all your help people.
 

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// Quandt AG (Retired) //
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Hey guys, thank you every so much for all your responses. I'm going to look into all that over the weekend and see what happens.

Iv checked coolant and bled the system, that didn't help. outside temp on showing correct on trip computer and the car temp needle is perfect as well.

I don't know if this makes any difference, but ever since I bought the car, when putting on the heaters, its always made a weird noise. Its almost as though it struggles and has asthma, heaters sound like their blowing out on/and/off very quickly but then after a short while the noise is a little more consistent like you would expect it to be. Would that mean anything?

Thanks again for all your help people.

Now that sounds like the FSR ( it is a resistor)

When you get heat blowing our of some vents and not out of others that can indicate a bad bleed job or the heater control valve I mentioned in the earlier post.
 
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