I believe that oil companies make oil specifically for diesels because ot the amount of particulates that contaminates the oil. So instead of using a 15W-50 Mobil 1 oil that would work great in that heat with a gasoline engine, you need to find a 15W-40 true synthetic that is designed for diesels. AMSOIL and Redline are two companies that make it but both are very expensive.

An alternative would be to use 15W-40 Shell Rotella oil designed for diesels. I think you can get it at Walmarts in the US.

I personally used 15W-50 Mobl 1 in my 190D diesel for the 17 years that I owned it and it never used a drop of oil. I use the same oil in my 300E in Arizona's triple digit heat.