Audi A4 B8 2.0TDI - Coolant temperature drops down when heater on

**IgorUK** · 09-12-2017,07:50 PM

Hello guys. My first post on here but i have a problem that noone can solve it so far. I have an audi a4 b8 2.0tdi from 2012. The car have some weird issue, when i turn on the heater the coolant temperature is dropping down and if im stuck in traffic or idling the engine for longer period the temeperature drops to 50-60 degrees and starts blowing cold air through the vents. The car had software aircon update done in august at audi dealership but i noticed the problem in october. The car is regularly serviced,3 month ago ive changed cambelt kit and water pump(. After that the egr valve got busted so ive changed that too.All work was done at audi specialist.Every part is geniune part. They tried to find the problem but they couldnt,changing the thermostat didnt solved the problem. They swapped a lot of parts for testing and nothing seemed to solve to problem. Now the car is at audi dealership for a month. They have also changed the thermostat once again under warranty and checked all the other changed parts and everything seems fine but the issue is still there. Ive told them about the software update and they said they have tested with different heater control panel but is the same, they are also saying that the software is fine. Is there any way to reverse back the old software before the aircon update? The car doesnt shows any fault codes. From what ive discussed with the audi specialist before is that once i press the heater on button the heater control valve probably stays fully open instead of partially opening to control the coolant flow. Honestly im not so good with cars but i was reading a lot since ive got the problem but still i have no idea whats wrong with the car. Im just surprised that even audi dealership cant find the problem. Im affraid i will end up with i car that cant be fixed. If anyone have any idea what can be the problem i will really appreciate your help.

**Gunnark100** · 09-12-2017,08:20 PM

So if you start your car and drive heater on...how long it takes car to warm up to 90 degrees?

You said dealer swapped many parts for test etc...what parts they tested?

**Audidua** · 09-12-2017,08:32 PM

Is your car facelift? I've had the same problem with my b8 2008 2.0tdi 105kW and solve it with replacing hidden thermostat 1K0 121 113A which is placed in rubber hose 03L 121 157 B which connects egr cooler and oil cooler. That hose is not part of newer engines on facelift cars.

**Gunnark100** · 09-12-2017,08:43 PM

Originally Posted by Audidua

Is your car facelift? I've had the same problem with my b8 2008 2.0tdi 105kW and solve it with replacing hidden thermostat 1K0 121 113A which is placed in rubber hose 03L 121 157 B which connects egr cooler and oil cooler. That hose is not part of newer engines on facelift cars.

Yes you did

....

Btw..fl hose nr 29 is very similar by diagram, only its now like part of "turbohose" 03L 122 157 Q, maybe same logic still...

**Audidua** · 09-12-2017,08:48 PM

Which diagram? Can you post the image?

**Gunnark100** · 09-12-2017,08:51 PM

Originally Posted by Audidua

Which diagram? Can you post the image?

Ignore language, check diagram....nr 29 long hose, at one end is attached very similar hose like on prefl and you see something has like two clips...like this tstat could be there between again...just a guess...

Audi A4/S4/Avant/qu. (2013 - 2015) - Ð–Ð¸Ð´ÐºÐ¾ÑÑ‚Ð½Ð¾Ðµ Ð¾Ñ…Ð»Ð°Ð¶Ð´ÐµÐ½Ð¸Ðµ. - VAG ETKA Online - Drive.by

**Audidua** · 09-12-2017,08:59 PM

Did you mean this part? It looks like hidden thermostat I must admit

**Gunnark100** · 09-12-2017,09:02 PM

Yep, looks f....ing similar to your prefl...

So OP, check this out on your car, maybe its there also and is the issue...

https://www.vwaudiforum.co.uk/forum/s...nt-temperature

**Audidua** · 09-12-2017,09:07 PM

Well, this is really interesting. I will take a look under the bonnet tommorow. If thats what we think it is it will be replaced first thing on next monday. I forgot to mention that now I have A5 2.0tdi 130kW facelift and also the same problem with coolant temperature on cold days.

**Gunnark100** · 09-12-2017,09:41 PM

Originally Posted by Audidua

Well, this is really interesting. I will take a look under the bonnet tommorow. If thats what we think it is it will be replaced first thing on next monday. I forgot to mention that now I have A5 2.0tdi 130kW facelift and also the same problem with coolant temperature on cold days.

I guess you find something there 100% as it was confirmed on 130kw c7 also...

Direct translation:
Do not look for piece code for that hose you will not find. It is part of the 03L 122 157 Q.