Hi. I am trying to help my brother with his car. He has a 2002 Golf GTI 1.8t and it is overheating. After driving for awhile, it overheats. When he goes into fith gear, it overheats faster. His coolant is dissapearing with no traces of leaking.(Possibly evaporating.) His fans are working fine. I would greatly appreciate it, I don't like to see him bummed at. Thank you.

 

Do the normal check up for overheating.

Check radiator cap, thermostat, etc...

Worse comes to worse, it's a head gasket.

 

Its probably the head gasket. the coolant is being mixed with the oil and just burning off. Check for white smoke (blue is oil) and a milky, somewhat thicker oil. Sorry.