1992 Mercedes 300E M103 -Replacing Thermostat For Summer Heat!

So teaching my son how to replace the thermostat on his 300E,
due to really hot temperatures coming up during the summer here, we install a 75c (167F)thermostat , it helps the engine run cooler.
During wintertime we put the stock 87c(188F thermostat back in.
Coolant to use is Zerex G5 it protects aluminum parts and its color is clear brown.