1st issue - coolant temp sensor, p2185 fault.
Coolant not reaching 90 degrees, rad fan was full speed from when the car was started, fuel consumption was very bad
2nd issue - once the coolant temp sensor was replaced, coolant temp was reaching 90 degrees only if car was stationary and temp was dropping close to 50 degrees if car was driven, or heating was turned on.
Audi a4 b8, 2008, 2.0 TDI, 105kw .
The issue was the 2nd thermostat ( has 2, yes) it was stuck open and coolant kept circulating and not getting to temp.