Maybe try changing the radiator? Not sure which one you're using but I always set mine to the high-performance or race option (can't remember the exact part name atm). Only thing is you can kinda see the radiator when its set to that since the performance radiator is grey instead of black. Edit: Also forgot to mention that I use a couple other mods for things like darker shadows and more realistic lighting since the latest BNG update really screwed a lot of paint jobs and stuff. Not sure if that would make any difference here or not.