I like MOCOOL
Think it's the same as "water wetter", but that's not for sale in Holland.
It's an half litre fluid to add to your normal coolant.
The murena radiator is too small for my rotary engine, and before mocool the temperature was between 90 and 100 degrees.
My temperature gauge dropped 10 degrees after adding mocool.
It's in my coolant for years, and never had a hot moment.