I had my CTS replaced by Audi (recall) last summer with a green one. It took the gauge 5 min to get to the middle point, where it's supposed to be. OK.

Then, I noticed when cruising downhill in gear, T drops by 10-15 C, which, I assume was because the drive-train was turning the engine, correct?

Now, at temps close to 0, my temp. gauge rarely reaches middle (90 C) as my commute is about 10 miles. And when going down-hill, the needle goes almost to starting position.

The other night, I started the car, let it warm up, and scanned coolant temperature through climate control ch. 51. So, while my gauge was showing about 80C, the ch.51 was reading 90 C. Now, the old saying - when you have two watches, you never know exact time.

TB and water pump (metal imp) done like 10k ago.

So, is it the green sensor again, or the thermostat? Although, I have heat, and I usually turn it on in the mornings when the coolant T is somewhere between cold and operating (90 C) temp. It's not like the air is hot, CC is off (Econo), just fan, and I see no problems with heat.

 

ohh, you got an 01, the thermostat in that thing is a bitch to change. its just 2 bolts, but i think human evolution is behind on the second elbow, 7 fingers and 2 thumbs involved on changeing it. but its only 10 bucks, try the thermostat.

 

sounds like tstat to me

 

I have hot air but it's not crazy hot i.e. when I set CC temperature to 23 C and start the heater, it's warm as expected. Increasing the T setting increases air T accordingly. So it's OK in that regard.

Does it mean that the thermostat is sticky or stuck open?

But I have to say that my climate control reads 90 C after 5 min idling, which means the engine gets warmed-up. It's just the discrepancy
between the climate control ch. 51 reading and the in-dash gauge reading. Doesn't the ch.51 read coolant temperature as well?

 

Does the ch.51 sensor read the same fluid as the CTS? Are they both in proximity?

 

and even heat is better.

Followed this
http://www.ray-cuthbert.com/audi/232/2009_10_08

 

i have a similar issue,
actually i am not sure if you have noticed it but when you start your car up in the morning does your rpm needle start from about 1500rpm then drops down to 750 when it warms up like it should or it just starts and drops to 750 as if its ready to go?

mine used to do the high rpm from start then drops down after a min or so when it was warmed up...
another thing the temp sensor barely reaches the half mark, when it does reach it its at lower speed then it fluctuates going up and down mostly staying around 11o'clock mark...
i am wondering if the CTS could be the issue here?

 

I had starting problems - first attempt failed, 2nd would start. T gauge fluctuating etc. But mine always started at 1500 and then dropped to 750 after 2-3 mins. all gone after I changed the CTS. but it was summer time and my T gauge would stay at 90 (190) most of time, except on long downhill slopes.

I guess you have to change CTS if it has not been replaced.