I'll offer another opinion regarding the SD.

Mine will show similar symptoms. It is just a question of how high the temperature will go. I can tell you that I cannot operate the SD in stop and go traffic with the A/C on with the ambient temperature above 85 or so. The gauge will immediately climb up to 100. I'm not about to find out where it stops so I roll down the windows.

My general consensus is that the system would need to have every part in it just about brand new, with no flow restriction of water or air for the temperature to remain at 95 degrees or less when running in stop and go traffic, 90 ambient, a/c on.

Both the SD and the SDL will run 95 degrees as a normal temperature when the a/c is on and the slightest amount of boost is used. Both of them can get up to 100 if the boost is on for 45 seconds or so. It does not even need to be full boost. Just a heavy pedal will do it.

I'm not really concerned with anything below 110 on both engines. I am quite sure that the SD will hit 110 if it runs extended boost (hills in PA) in 90 degree ambient with a/c.
I don't have enough info on the SDL yet, but, I would not be surprised for it to do the same thing.

I did get a benefit of about five degrees or so on the SD by removing the radiator and thorougly cleaning the fins. It is quite amazing how much crap will accumulate in there, and, unless you look carefully, you will not see any of it