GMC SIERRA CK2 1999 Owner's Manual page 263

3. Fill the radiator with the proper DEX
coolant mixture, up to the base of the filler neck.
(See "Engine Coolant" in the Index for more
information about the proper coolant mixture.)
R
-
COOL 4. Then fill the coolant recovery tank to the
COLD mark.
5. Put the cap back on the coolant recovery tank, but
leave the radiator pressure cap off.
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