Audi A4 B8 2.0 TDI looses temp when not on throttle

[erikdude27]

Hi!

I have got a 2011 Audi A4 2.0 TDI 6-speed manual. The car works like a dream and has a perfect power delivery. The tune is a 177HP / 390Nm stage-1 tune.

While driving in degrees around or lower than -5C, the coolant will lose temperature if I'm not on the throttle. Meaning that if I'm coasting downhill for a few minutes with fuelcut and the climate control on 22C, the temp will drop to around 80C.

Then when the hill level out and I apply throttle, it quickly climbs to a 90 degrees and stays there while having throttle open at normal position. It has never in my ownership exceeded 90 degrees in any circumstance, even when +20c at wide open throttle on Autobahn, or revving it to 4,500 o/min in 25C.

As I mentioned earlier, the car works as it should and has a stable idle and great power response. But I wonder if this is normal, and if so - why? Is it simply because the climate control draws so much heat from the coolant while the engine is producing little to no heat?

Thank you for some clarification on this!

Erik

 

[Breezey]

Sounds like the thermostat may need replacing, I’ve had this issue on a few Audi’s now and when they go the coolant circuit is fully open so when costing etc it doesn’t close to create the short loop to enable heat to be brought back into the coolant. Just my thoughts anyway!

 

[erikdude27]

Sounds like the thermostat may need replacing, I’ve had this issue on a few Audi’s now and when they go the coolant circuit is fully open so when costing etc it doesn’t close to create the short loop to enable heat to be brought back into the coolant. Just my thoughts anyway!

Thanks for the answer!

That sure does sound plausible. I did however observe something interesting the other day. I stopped at a gas station to check a few messages on my phone right next to the highway, and only a few minutes of idling brought the temperature down to some 80 celcius. This is with the cabin heater on 22.0 degrees C.

It seems that the cabin heater might be drawing a lot of heat off the coolant. One would imagine that the cooling effects from running the coolant through the radiator when stationary is negligible - or am I wrong on that?

Also, does this effect the engine oil or block heat? We aren't talking a long time here, only a few minutes at the most. I'm placing my bets that this doesn't have much, if any, effect on the engine at all.

I'd love to hear what you think. Cheers!

 

[Breezey]

Definitely sounds like the thermostat to me, the cabin heater does draw a lot of heat from the engine particularly in cold weather it can take an age for the 2.0L TDI to actually reach its proper running temperature. Having said that it could also be the temperature sender but from what you are describing with the small amount of idling and the temperature dropping I would put my money on thermostat. The Audi cooling systems are very efficient so when the thermostat goes the engine almost never reaches optimum temperature.


It’s an easy process and one I undertook myself on my A4 1.9TDI few bolts and buckets later it was all swapped and solved the very same problem you describe.


I’m Not sure what you mean with the engine oil, the 2.0l isn’t a very high performance engine so doesn’t have seperate oil coolers etc so that would have no effect on reducing the temperature I wouldn’t have thought.

 

[erikdude27]

Definitely sounds like the thermostat to me, the cabin heater does draw a lot of heat from the engine particularly in cold weather it can take an age for the 2.0L TDI to actually reach its proper running temperature. Having said that it could also be the temperature sender but from what you are describing with the small amount of idling and the temperature dropping I would put my money on thermostat. The Audi cooling systems are very efficient so when the thermostat goes the engine almost never reaches optimum temperature.


It’s an easy process and one I undertook myself on my A4 1.9TDI few bolts and buckets later it was all swapped and solved the very same problem you describe.


I’m Not sure what you mean with the engine oil, the 2.0l isn’t a very high performance engine so doesn’t have seperate oil coolers etc so that would have no effect on reducing the temperature I wouldn’t have thought.

Then I'll be taking a closer look into it. When it's very cold (<-12C), the temperature can slowly be shifting between 80/85-90 on the short downslopes of the highway. It definitely cools very fast.

What I meant was that, does it matter for anything really if the temperature drops a little? I mean, the oil and engine block will remain the same temperature (at least very close) - so it won't affect wear or performance on the engine.

Keep in mind that the engine is tuned - not sure if this can have an impact on the heat creation of the engine over stock mapping.

 

[Breezey]

Fuel economy will be the main thing effected until the engine reaches its optimum temperature more fuel is used to get it there. Effected my A4 by 10mpg. It should be a cheap fix worth doing as the longer you leave it the more t will cost in fuel.

 

[erikdude27]

Fuel economy will be the main thing effected until the engine reaches its optimum temperature more fuel is used to get it there. Effected my A4 by 10mpg. It should be a cheap fix worth doing as the longer you leave it the more t will cost in fuel.

Understandable. I'll try to get it done as soon as I can. Frustrating to see the needle drop while driving

 

[Breezey]

Understandable. I'll try to get it done as soon as I can. Frustrating to see the needle drop while driving

Obviously I’m no mechanic I can only comment on how it sounds to me. I have had this experience in the past and resolved it. Good luck

 

[erikdude27]

Obviously I’m no mechanic I can only comment on how it sounds to me. I have had this experience in the past and resolved it. Good luck

Of course, I'm very happy with any ideas and possible causes. Thank you!