GMC 2003 Envoy - Manual (Page 330)

Start the engine and let it run until you can feel ine
upper radiator hose getting hot. Watch out tor toe
engine codling (an.
By this time, the cooiani level Inside the radretor
ftlter neck may he lower* II the level la lower* add
mgra of the proper □EX-COOL'® coolanl mixture
through (he filler ngcii until the level neaches
toe base of tha filler necti.
Then replace the pressure cap, Al any tirne during
this procedure if cooiarrt begins to flow ool oi the
filler neck, reinstall ihe pressure cap. Be sure
the pressure cap is hand-iighj,
Engine Fan Noise
This vehicle has a clutched engine cooling fan* When the
clutch is engaged, the fan spins taster to provide moro air
to cool tha engine. In most everyday driving condilions
(he cJutch is not engaged. This Improvasfuef economy
end reduces fan noise. Under heavy vehicle loading,
trailer towtog, and/or high ouisida temperatures, the fan
speed iocFoases when the dutch engages. So you may
hear an ir>crease in too noise^ This is normal and should
not be mtstaken as the transmission slipping or making
e)dfa shifts. It is merely the cooling system functioning
properly. The fan will slow down when additional cooling
is not required and the clutch disengages.
■/ou may also hear this fan noise whan you slart Ihe
engine, It will go away as the Ian dutch disengages.
&-Э5