You won't get engine damage til you get up to the red zone, and I can see getting pretty hot stalled in, say Houston, with a slight following breeze at 4 pm in traffic.

However, you are running too hot. Do the quicky test for visco clutch operation (shut off when it is that hot while watching fan, it must stop within one revolution), and replace the thermostat (big PITA, it's on the side, in the lower radiator hose connection, you have to do it by feel). If the temp stays up, it's not the thermostat

If the visco fan and thermostat are OK, and the radiator cap holds pressure (check it, it's cheap) replace the radiator, it's MUCH cheaper than a new head. Flushing won't work if someone has been using green coolant in the past, the rad is full of insoluble crud, and you CANNOT remove the tanks and reinstall them leak free, no matte what anyone says. You are probably stuck with a plastic and aluminum replacement -- not enough demand for brass and copper ones (sadly, they last forever).

I'm fairly certain the techs have checked the temp across the rad -- easy to do these days with infared thermometers, and found cold spots indicating plugging. Rad is about $300 plus installation

My 300D had a new rad when I got it, but it has green coolant in it, to be changed this summer.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!