[Eljaro]

You might be right , Brent, but the engine has no new pistons, which is what generates most of the run in heat. It could well be that the fan does not cope with heat generated at 2000rpm during 15 min. at standstill. The air temp here is about 34ºC right now, quite hot.
I will take a ride tomorrow and see what happens with the temp while in motion.
Anyway, I still would like to know what the bypass really does and why someone may want to plug it.