I just checked mine this morning and it would not go over 69C in suburban stop and go. Temp outside was a few degrees below freezing. (Car has over 80k miles)

Since it had just done a 40 minutes run with few stops on two lane roads I think it should be running above 80C. Tomorrow the wheather should be a few degrees over freezing and will check again but I suspect my T-stat is toast.

Diesels may not warm up fast but they certainly should be able to attain the T-stat stated temperature in moderate weather.

__________________
2003 4.4i black ext./black int./black headliner (kid's runabout)
2014 535d X-drive, M package, silver/black interior

Sold but not forgotten:
2009 E70 35d, black ext./black int./black headliner (sold 2021)
2006 4.8iS Le Mans blue/cream int./black headliner, SOLD in 2012 sadly...

Other hardware:
2015 Cayenne S (wife's new DD and definitely wroooommmmm)
2016 Tundra 1794 edition crew cab, luxo hauler
2005 Tundra crew cab, weekend hauler. Sold after 150k very happy miles.