GMC 2003 C4C042 Owner's Manual page 292

Adding Coolant
If you need more coolant, add the proper DEX
coolant mixture at the surge tank, but only when the
engine is cool.
CAUTION:
You can be burned if you spill coolant on hot
engine parts. Coolant contains ethylene glycol,
and it will burn if the engine parts are hot
enough. Don't spill coolant on a hot engine.
When replacing the pressure cap, make sure it is
-
hand tight.
Engine Coolant (Caterpillar
Diesel Engine)
If your vehicle has a Caterpillar diesel engine, see the
R
Caterpillar Diesel Engine Operation & Maintenance
Manual provided with your vehicle to find out what to
add, also when and how to service your cooling system.
6-38
Surge Tank Pressure Cap
R
-
COOL
The surge tank pressure cap must be tightly installed.
NOTICE:
R
Your surge tank pressure cap is a 15 psi (103kPa)
pressure
cooling systems only. It must be tightly installed
to prevent coolant loss and possible engine
damage from overheating.
The surge tank pressure cap
is located in the engine
compartment, on the
driver's side of the vehicle.
-
type cap for use with medium duty