Delo 15w-40 in 91 300E for oil change?

[JordaanDMC-12]

I have a real quick question, I remember reading on a thread that many of you who own 300E's put diesel oil in them for an additive that in not manufactured into normal gasoline engine oil anymore and also for the fact the diesel oil has many detergents that help keep a 300E's crankcase squeaky clean.

My question is, is it alright to put Delo 15w-40 in my 300E? That's all I can find of Delo, no lower viscosity. The temperature has been fluctuating here quite a bit, it's kind of spicy here one day (76-77oF) and then can get to (36-47oF) is this oil viscosity ok to put in?

thanks all