CHEVROLET 2009 Suburban - Manual (Page 433)

If no coolant is visible in the surge tank, add coolant as
follows:
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.
Turn the pressure cap slowly 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. Keep turning the pressure cap slowly and
remove it.
3. Fill the coolant surge tank with the proper mixture
to the FULL COLD mark.
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