GMC Sierra Denali Owner's Manual page 301

How to Add Coolant to the Coolant
Surge Tank
If you haven't found a problem yet, check to see if coolant
is visible in the surge tank. If coolant
is
visible but the
coolant level isn't at or above the FULL COLD mark, add
a 50/50 mixture of clean, drinkable waterand
DEX-COOL@ coolant at the coolant surge tank, but be
sure the cooling system, including the coolant surge tank
pressure cap, is cool before you do it. See Engine
Coolant on page 5-24 for more information.
/ ; 1 CAUTIC I:
Steam and scaldin, ,iquids from a hot coa ....g
system can blow out and burn you badly.
They are under pressure, and if you turn the
coolant surge tank pressure cap
-
even a
little
-
they can come out at high speed.
CAUTION: (Continued)
Never turn the cap when the cooling system,
including the coolant surge tank pressure cap,
is hot. Wait for the cooling system and coolant
surge tank pressure cap to cool if you ever
have to turn the pressure cap.
5-32