Where is the best place to check if my car is using coolant ? Thanks

 

Radiator, as the plastic ends can split

 

Do i check the coolant level at the header tank or radiator cap? There does not seem to be a leak . I just want to check if the level is going down or not. Smoke is coming from the turbo area, think it may be leaky up-pipe gasket, Im just eliminating 1 thing at a time. Thanks

 

Header cap

 

WILL CHECK IT