GMC 2009 Sierra - Manual (Page 343)

How to Add Coolant to the Coolant
Surge Tank
If you have not found a problem yet, check to see if
coolant is visible in the surge tank. If coolant is visible
but the coolant level is not at or above the FULL COLD
mark, add a 50/50 mixture of clean, drinkable water
and 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 5-23 for more information.
If no coolant is visible in the surge tank, add coolant
as follows:
{ CAUTION:
Steam and scalding liquids from a hot cooling
system can blow out and burn you badly.
They are under pressure, and if you turn the
radiator pressure cap — even a little — they
can come out at high speed. Never turn the
cap when the cooling system, including the
radiator pressure cap, is hot. Wait for the
cooling system and radiator pressure cap to
cool if you ever have to turn the pressure cap.
5-31