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I just wanted to update this thread to say that I was wrong!!

It wasn't the coolant. I tried swapping out the green and replacing with G12 and the Code came back. Also the sensor was replace but the code came back after a day.

So on the weekend I bit the bullet and replaced the thermostat. What a PITA job on my A3 but in the end everything is working fine now and temp sits perfectly in the middle of the gauge.

There are lots of tips I could give someone that wants to do this. So if any of you want to change this part be aware it's not fast or easy. If you don't like getting your hands dirty and don't have patients then just take it to the dealer haha.
 

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Bumping this thread - As I am trying to figure out what to try next.

2005 Audi TT 3.2 (DSG) - Car has been experiencing long warm up times. In 55*F weather, it took the car 20min at idle to reach temp. I did the same test on a friend's r32, it took his car roughly 7-8 minutes (Same day, cars were next to one another). On a colder day like today, around 25-30*F, it took over 20min of DRIVING to get to temp. This is the same for warmer weather as well, just marginally worse on colder days. The car is garage kept, so 50-65 ambient temp in the garage, not an ice cold motor. Soft code P2181 registered via VCDS but I didnt check freeze frame data.

I have had this issue for about 16-18months, it has persisted regardless of the following repairs done in that time since first observing this code and slow warm up times.

  • Greentop CTS (on my 3rd OEM unit now)
  • OEM 80*C Thermostat (on my 2nd one of these just to rule it out)
  • 50/50 G12 mix with distilled water. Always changed with every job.
  • New OEM Audi Fan Control module
  • New Fans
  • New Radiator
  • New Reservoir/Globe
  • Wiring on connector of CTS looks good
  • Resistance checks out on CTS itself when cold (haven't tested this when running, not sure how?)
  • Rebuilt Gauge cluster
  • Replaced 1-way valve located in hose between aux pump and DSG cooler. One that was removed was not stuck though

So, I don't think its my thermostat, I don't think its my sensors. Reading the above posts im inclined to start a new mixture of 60/40, reducing the antifreeze content. I also discovered there is another 1-way valve on a different hose that also leads to the DSG cooler (didn't realize there were two of these). So I will also replace that. Last idea will be to check wiring to the CTS and near ECU for any damage or migration. But the heat does not return hot air until after it gets to temp, so I dont think I have a sensor or bad signal. I seem to be experiencing a true slow warm up.

I have seen a few 2.0T DSG threads turn up citing those one-way valves for causing under heating, its the only thing that makes sense to me based off everything I have tried. What else could cause a car to not warm up? Fans being on? (they are not) poor tuning? Over-efficient cooling? (I have the CSF radiator, and an A/C delete, but this shouldn't matter if the Tstat is indeed closed during warm up.)

SOS!
 

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I also discovered there is another 1-way valve on a different hose that also leads to the DSG cooler (didn't realize there were two of these). So I will also replace that. Last idea will be to check wiring to the CTS and near ECU for any damage or migration. But the heat does not return hot air until after it gets to temp, so I dont think I have a sensor or bad signal. I seem to be experiencing a true slow warm up.

I have seen a few 2.0T DSG threads turn up citing those one-way valves for causing under heating, its the only thing that makes sense to me based off everything I have tried.
Bump for anyone who encounters this thread - I removed the cooling hose that ran from the AUX pump to the DSG Cooler, and sure enough the 1-way valve was stuck open, allowing flow in both directions. Looking at the cooling diagrams, this technically allowed for some thermostat bypass to the rest of the cooling system, likely causing my underheating/slow warm up issue. The part # for this valve is 1J0-122-351. On a DSG TT 3.2 like mine, there are two of them. On other 3.2's there is just one between the lower rad hose and Aux pump, and this valve is usually included with the hose assembly from factory.
 
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