GMC SIERRA CK2 1999 Owner's Manual page 313

Adding Coolant
If you need more coolant, add the proper DEX
coolant mixture at the coolant recovery tank.
CAUTION:
Turning the radiator pressure cap when the
engine and radiator are hot can allow steam and
scalding liquids to blow out and burn you badly.
With the coolant recovery tank, you will almost
never have to add coolant at the radiator.
Never turn the radiator pressure cap
--
a little when the engine and radiator are hot.
Add coolant mixture at the recovery tank, but be careful
R
not to spill it.
-
COOL
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.
--
even
CAUTION:
yellowblue
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