I've driven many VW and Mercedes diesels in AZ, and they all run hot when it's that hot outside. Especially in stop and go, in town driving. Climbing mountain grades in 115 degree heat causes the engine to run hot. Even my Mom's Cadillac Diesel ran hot going over the mountains between Phoenix and Sedona. These were new cars at the time, so there was nothing worn out. Diesels produce more heat climbing hills, than a gas engine does.

Temps over 115 are near the top of the safe operating range. You have to watch your temperature gauge and take it easy.

Although 95* and high humidity feel hot to your body, it's easier for your car. The extra 20-25 degrees makes a huge difference to your car.

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1979 240D, 4spd manual, Power Sunroof, manual windows, 147k miles, Pastel gray/Black MB Tex.
1991 300D 2.5 - Smokes like it's on Crack!