Chevrolet 2007 TrailBlazer Owner's Manua page 416

If you have to add coolant more than four times a
year, have your dealer check your cooling system.
Notice: If you use extra inhibitors and/or
additives in your vehicle's cooling system,
you could damage your vehicle. Use only the
proper mixture of the engine coolant listed
in this manual for the cooling system.
See Recommended Fluids and Lubricants
on page 529 for more information.
416
Checking Coolant
The vehicle must be on a level surface. When
your engine is cold, the coolant level should be at
FULL COLD, or a little higher.
The engine coolant
recovery tank is in the
engine compartment on
the passenger's side of
the vehicle. The cap has
this symbol on it. See
Engine Compartment
Overview on page 396
for more information on
location.