I have a 2011 CMS All4 that for some reason after an hour of drive, the coolant fill tank is still cold. feeling the pipes below the air duct, one is hot and the other cold. I replaced the thermostat housing, no change! i replaced the water pump, no change!

is it normal for the fill tank to remain cold? my other R55 and R56 get hot within minutes and that's what im used to !

 

Updating my post.

The water pump was fine...The culprit was ME...during installation of the front end, i must've flipped the hoses going to the radiator. I bought a new thermostat housing. everything turn out fine.