Well, perhaps the engine is more updated than expected - 

 

Coolant regulator housing

• opening start: approx. 88°C
• opening end: approx. 103°C

 

Thermoswitch for radiator fan

or for both fans (a/c)

switching temperatures:

 

• Stage 1:
• on: 91 through 97°C
• off: 84 through 91°C

 

• Stage 2:
• on: 99 through 105°C
• off: 91 through 98°C

 

Edited 29 December, 20214 yr by nta16

10 hours ago, J.R. said:

Lean burn = higher combustion temperatures but would the normal operating temperature of the coolant be higher by design?

 

80°c does seem rather low for thermostat fitted for a European country.

 

It isn't, most diesels are around 80 degrees.

 

Yes lean burn engines run much hotter although the coolant is only a bit hotter due to different radiator sizes and pump flow rates.

 

The problem here is that there is no problem. OP is worrying about nothing, a nice cool AQW will not suffer HGF.

 

IIRC I fitted a special low temperature thermostat to my VR6, 78 degrees I think, it ran much better as a result anyway.

Thanks for that, I knew there had to be a reason for lower temperature thermostats, diesel is obvious in hindsight.

 

All 3 of my VAG diesels have read spot on 90°c on the temperature guage, - OMG I have a problem, it should be 80°c!! 🤣

 

Hello all. The problem it is solved. I reclaim the thermostat and I am waiting for the answer. Meanwhile i bought another thermostat rated to 88 C. The car runs now in open road at 90 C. I went to the city with traffic lights and to highway to test and in the end the average mileage by ECU was 6.7 l/100 that mean 7.0 real. I really see an improvement. The AQW engine has 2 lambda probes, catalytic converter and obeys to EURO 4. 82 C not the right temperature. Thank you all for your time and attention. Have a nice new year.