GMC 2008 Yukon XL Denali, Owner'S Manual, Page: 370 / 502

Notice: In cold weather, water can freeze and crack
the engine, radiator, heater core and other parts.
Use the recommended coolant and the proper
coolant mixture.
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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. Do not spill coolant on a hot engine.
1. You can remove the
coolant surge tank
pressure cap when the
cooling system,
including the coolant
surge tank pressure
cap and upper radiator
hose, is no longer hot.
Remove the coolant surge tank pressure cap by
slowly turning the pressure cap counterclockwise
about one full turn. If you hear a hiss, wait for
that to stop. A hiss means there is still some
pressure left.
2. Then keep turning the pressure cap slowly, and
remove it.
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