2012 Chevrolet Avalanche Owner's Manual - Page 349

Vehicle Care 10-19 { WARNING 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 surge tank pressure cap - even a little - they can come out at high speed. Never turn the cap when the cooling system, including the surge tank pressure cap, is hot. Wait for the cooling system and surge tank pressure cap to cool if you ever have to turn the pressure cap. If no coolant is visible in the surge tank, add coolant as follows: 2. Keep turning the pressure cap slowly and remove it. 1. 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 a hiss is heard, wait for that to stop. A hiss means there is still some pressure left. 3. Fill the coolant surge tank with the proper mixture to the FULL COLD mark.