It seems that MB diesels built after 1985 run hotter. When I bought my "87 SDL (new), it ran about 88-92C on the open road, (Don't remember the city temps.) Last summer I got a new water pump, t-stat, and much needed fan clutch. Now it runs at 88-92C on the open road (even in 20F weather) and approx 98-103 in city traffic in 100F summer weather. According to published specs, the aux fan doesn't even click on until about 105C ! My 1987 (SDL) manual and my 2000 (ML, gas) manual state - and I quote from the manual: "During severe operating conditions and stop and go traffic, the coolant temperature may rise close to the red marking." The 2000 manual goes on to say don't run the engine in the red marked area. I figure that the temp. gage may be off about +- 5C. Also, in commerical truck diesels, a hot diesel is far more efficient than a cool running one. Of course, what we are all discussing is what is too hot. Now, if you are running 105 - 120 C on the open level road, I'd say that you have a problem.
