Hi, i have a audi A4 2012 with 2.0 100kw CJCA engine. The problem that i have is with the coolant temperature. When i drive the car its all ok until i power on AC/Heater in these cold days. It doesnt mater if the AC is on or just a regular heater the temperature drop quickly. When i turn it off the temps go up. I have changed the main thermostat, the seccond one also and the small somekind of ventil that has just a tube and a ball in it. Can anyone help me with the problem?

Thank you.

I suspect the main engine fan is running continuously, instead of only when needed.

I scanned the complete system with VCDS and no errors. I was watching the fans and they only spin when the AC is on or the coolant temperature goes above i believe 94. I also tested with vcds how fast is the temperature going down. So, when the heating is off, ac off, its all normal with the coolant temperature. When i power on heating without AC it goes down prity fast. Same test with the AC on and it goes down at same speed.... But... If i put the blower on max the coolant temperature is going down even faster.

At the end. Fans are ok. Thermostats are ok. The small ventil in a hose is ok. No error codes. The problem is there only when heater or AC are on and if the blower is on max the coolant temperature goes faster down than when the blower is on minimum.

I would like to say thank you to everyone who is trying to help me.

Also i forgot to mention that when i power on the AC the fans start spinning but the coolant temperature goes down at same speed as when the AC is off and just the heating is on. The only thing that does impact the speed of cooling the coolant is the blower inside the cabin. If its blowing fast the temps goes down faster, if its blowing slow the temps also goes down but not as fast.

In that case I am at a loss to explain the fault, unless there is an electrical fault with the temperature guage. Can you check the coolant temperature with an independent guage such as a hand held infra red instrument?

With VCDS i can see two sensors for coolant temperature. One says just COOLANT TEMPERATURE and the other says the same and in addition AT ENGINE BLOCK, something like that. Those two are not the same, there is a 1 to 2 degrees difference. And both are going up and down. So i don't believe that its the sensor in the fault.

I have additional pump somewhere, can that be a problem? Maybe it can be problem with it?

So, no one has some other ide where to look for the problem? I still haven't found it.

4 hours ago, Gogo said:

So, no one has some other ide where to look for the problem? I still haven't found it.

 

Does driving at 70 mph make the coolant temperature drop , or does it hold steady ?  At 90 degrees I believe..  

Edited January 5Jan 5 by Audisq524

On 1/5/2026 at 10:21 PM, Audisq524 said:

 

Does driving at 70 mph make the coolant temperature drop , or does it hold steady ?  At 90 degrees I believe..  

It drops. Scheduled for new thermostat (even my is around 6 months old) because on friends car the same manufacture of the thermostat failed after 2 months. Now i put Mahle and we will see.