Car heater, too hot or too cold

[L3nny]

The heater on my BMW 320D E91 doesn't get hot unless you put it on the highest 28 degree setting which is then too hot.

Anyone have any ideas what could be wrong?

[AlexAdams]

What year is that, at a guess your thermostats have failed

[L3nny]

It's 2010, if the thermostat had failed I'd expect it not be be getting hot at all.

[ophic]

No, I think they work on the principle of max heat until ambient temp (indicated by thermostat) hits the required value. But the highest setting just ignores the thermostat and pumps out max heat permanently.

[andrewsmith]

Could be worth checking the cabin filter. Fixed the issues I had the heating and cooling performance on my car.

They do rely on an air flow to perform properly and the engine temperature

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[L3nny]

Had the car serviced last month and they replaced the cabin filter then. I pulled it out anyway and had a look and it does look pretty new.

I've also been monitoring the coolant temperature using ter Torque app on my phone and a Bluetooth OBD adapter. It's sat a a constant 80-85c.

[maviczap]

Could be the thingy that takes the heat from the coolant to your heater is gummed up. Can't remember what its called, but a mate had a similar problem on another car.

[Red ones]

How accurate is the outside air temperature sensor?
They don't just give a nice little display for the driver, but also determine whether any hearing or cooling is needed for the cabin (and also determine fuel air ratio for the engine amongst other things)


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[ophic]

Could be the thingy that takes the heat from the coolant to your heater is gummed up. Can't remember what its called, but a mate had a similar problem on another car.
Heater matrix?

[Mark_h]

It'll not start blowing in anger until the heater is significantly hotter than the current inside car temp. Prior to that it will blow but not hard. Around the heater control area you'll find a little (about the size of a micro SD card) grill with a fan behind it. This is where it samples the cabin temp. When mine was clogged with fluff it went a bit weird so give that a clean out.

My old BMW had a heatsink controller for the fan motor. This failed and then the fan was either off or very very on. This was a right bugger to get to but once swapped out all worked fine. Not sure if the newer BMWs still have these or where they live. BMW forums refer to these as Hedgehogs.

Oh and also on the 5-series you set target cabin temp with one control but can also set the dash vents to blow hot and/or cold regardless of the cabin temp. May be worth checking you've not got the dash vents set to cool while trying to lift the cabin by 15degrees.

[L3nny]

I'll have a look for the cabin temp sensor and check that. That being faulty would make the most sense to be honest.

[L3nny]

Okay, I have fixed the problem. It's now keeping the car at a comfortable 21 degrees. Have a look at this picture and see if you can work out what the problem is. :rolleyes:

http://i.imgur.com/3yem3SI.jpg

[maviczap]

GPS is telling the computer its near the North Pole, so wack the heat up :-)

[Mark_h]

It'll be the knob set to blue making sure all the vents squirt cold air. Then biasing the heater to those vents.

Auto button then turn off aircon and all will be fine most of the time. Adjust the thumb wheel for what temp you want in your face.

[L3nny]

It'll be the knob set to blue making sure all the vents squirt cold air. Then biasing the heater to those vents.

Auto button then turn off aircon and all will be fine most of the time. Adjust the thumb wheel for what temp you want in your face.

I think the problem was more the knob behind the steering wheel but yes you are correct.

[maviczap]

Too many knobs :-)