My '91 350SDL w/ 126Kmiles is running hot--radiator, water pump, and thermostat replaced in 6/04. Temp gage reads as follows after warming up with ambient temperature in the mid-90's:
20 -50 mph = 105C/200F
60 mph = 110C/208F
75 mph = 115C/216F
Otherwise, engine is strong and smooth running with no unusual oil usage.

How long has this been going on?

Is the A/C condenser, in front of the radiator, clear? A collection of bugs can block air flow, and more speed won't help.

Is there any difference above 40 mph with and without A/C? The new radiator may be partially plugged, or the new pump may not be flowing enough coolant.

Did this develop right after the radiator, pump and thermostat were replaced? Some thermostats have been 'bad' right out of the box, and on top of that, they can be installed upside-down with bad results...

Is the upper radiator hose stiff and under pressure even after the engine has cooled off? A blown head gasket can result in hotter temps.

Best Regards,
Jim

My wife drives this car most of the time and we've been noticing this behavior since early summer but it seems to be getting worse. To answer Jim's questions, A/C condensor is clear, seems to run cooler with A/C off, upper hose is not stiff when cold or after running at temperature. There is no loss of coolant and no evidence of blown head gasket. Recently replaced one of the fans but no noticeable difference with both fans operating.

when you replaced it? perhaps the stat is bad.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I'm far from a Mercedes expert.So I don't know the particulars on you'r engine.But I do know if you'r injector pump timing is off to much either way,it can cause you'r engine to run hot like this.But I think a bad thermostat is you'r most likely problem.