have four diesels. profile check will provide details. the bugger of the moment is the six cylinder item with the aluminum head. yes, 86 300sdl. have not been using it lately as it has been very hot and the temperature guage will readily pass the 100 mark. none of the other diesels moves much above the steady state 82 or so mark. have read all the search results. thermostat change twice. cooling system flushed and filled with proper mb antifreeze. what i find puzzling is that almost immediately as i drive up a little 'rise' the temp climbs maybe 10 degrees shortly as i start the climb. any 'aggressive' acceleration results in temp guage's responding within seconds. is this normal? acceptable? again, none of the others behaves in this manner. thank you.

Mine does the same thing. The temperature gauge might as well be a boost gauge. Even in cold weather, the temp will climb close to 100°C. if heavy pedal is used. On Sunday, a/c on, climbing some hills on the Taconic Parkway at 80°F. with 700 lb. onboard, she peaked at about 102°C. But, on the downhill, it drops right back to less than 85°C.

The SD, with the 617,does not behave in similar fashion.

I don't even worry about it. If it climbs above 105°C., then I might consider backing off the power. But, it hasn't happened yet.