Hello and welcome to Just answer.com, Super mechanic here. About your vehicle.
The first thing that you want to do is check the cooling system for any exhaust gases. There is a tester for that, that you can gt from Autozone for about $20.
Block tester available as:
Snap-On GDCT16
Napa BK. XXX-XXXX
If there are any exhaust gases in the cooling system, that will cause more pressure than desired and will probably allow the engine to burn coolant.
If there are, then there would be an internal engine problem, like a head gasket or head.
Is there a egr cooler or any other way exhaust can get in coolant. Where does the small coolant line from the back of the top radiator pipe connect too. It looks like it goes under the turbo.
Whenever there is exhaust in the cooling system, it is either one of the heads or one of the head gaskets, (or both)
The small hose goes to the intake manifold
Master technician
29 yrs. exp., ASE master, cert. in G.M. electrical, a/c, susspension, brakes, electronic steering