After seeing all the posts in here about elevated running temps on the turbodiesels, just thought I'd mention one often overlooked item. My 82 300 TD had the same problem even after replacing the whole cooling system. I had finally given up and thought maybe it was just a slighty tired engine having to work harder or maybe a gremlin or two in the 20 year old wiring. That is until about a week ago when I was about to change my oil and I just happened to place my hand on the oil cooler and it was stone cold. And this was after driving it home from work in 85 degree weather. It was like an epiphany. "So this is the culprit", I thought to myself. Well, after replacing the oil cooler thermostat, which is located in the oil filter housing, my temp gauge is back down to where it is supposed to be, just above the 80 mark. I know that this is overlooked because my parts supplier said that he very rarely sells the thermostats. So people check those oil coolers, they too are part of the cooling system and they are there for a reason. If they are cool to the touch after driving the car hard, then they are not removing heat. By the way , I think the thermostat is fully open at 110 degrees (celsius I would think)