2.0TDI 177BHP - Never reaches 90C temperature

Always sit at 70-80C, I had only 2 instances where temp reached 90C for like 1 minute max, just had 15 miles drive and another 15 miles of spirited drive on top and didn't see single time temps reaching 90C, surely thermostat issue.

After doing my own research it seems like it's super common with these engines, and everyone from old threads saying its normal, but I really doubt it, my auto start/stop also doesn't work, maybe because temp never at 90C or maybe I don't know how to use it, as I just bought this car. I also have lower economy than expected, driving nicely 40-43mpg, Spirited 34-37mpg, seems like I'm missing 5mpg or so imo. Any thoughts ?

I would go for the thermostat, sounds like it’s stuck open. Not sure if it’s an easy job on this engine, it definitely is not on my TT. The temp will also have an effect on your consumption and may well also limit the function of stop start. Once the temp is resolved then look at the other issues if they still persist…

If the gauge never reads 90 then something is wrong as it should read 90 at a real 77 and still read 90 at 116, it is the way VAG program them to stop people whittling about the readings minutiae.

There are two thermostats I believe how would one know which to replace ?

This may assist.
Audi Parts catalog - ETKA Online, Audi EUROPA, original Catalog Audi EUROPA

PM me your reg

Assuming you have a DSG gearbox.

It's almost always the DSG cooler thermostat that fails open, this then short circuits the cooling system & overcools the whole engine.

Follow the coolant pipe from the DSG & you will find the in-line thermostat nearby.

My 3.0 tdi A6 gets to 90 c after about 3 miles in winter and sooner in summer. My 2.0 tdi A4 takes 8 - 10 niles in the winter and about 4 miles in summer. If i put on cabin heater in the winter it drops to about 80 c. I considered the thermostat to be faulty so asked for it to be changed under warranty. The dealer said this is normal for 2.0 tdi. I disagreed and asked for it to be changed. The result was no difference at all. To be honest i have my suspicions that they never did change it but can only prove it my going to an indy and paying for another replacement stat. For me a car should be able to reach 90c for tdi and maintain that temperature.
in short I think your thermostat is stuck open.

Ignore what modern VAG temp gauges read, it is programmed to get to 90 ASAP and stay there to stop people whittling about the minutiae of tiny changes, if it doesn’t something is wrong.

I had the exact same problem - precisely as you experienced, bang on. It was the thermostat at the front near the alternator that I had replaced and it solved the problem - ie. not the other thermostat that is difficult to get to at the back of the engine.