first off, don't take advise from anyone that has no experience with the OM603 engine in either a 124 or 126 chassis. These cars run hotter than the ones with OM617 engines. this has been said by gsxr also, and there were sugestions in one thread that the best thing a owner of one of these engines can do is put a nice big therm gauge on the dash!
see thread:
http://www.peachparts.com/shopforum/showthread.php?t=102579&highlight=1.4+bar
It's a fact of life that the cooling systems are different between the 603 and other diesels made prior. There is a fuel heater for one thing. And I think the radiator is a bit undersized, and there's the under pan that might affect airflow across the rad fins, I dunno. Are you running a 1.4 bar cap?
I use Redline Water Wetter, I have a new radiator and a new water pump and a #14 head and mine runs about the same as yours under similar conditions.
Just take it easy and there shouldn't be a problem. (knock on wood!
