2011 Chevrolet Impala Owner's Manual - Page 276

10-20 Vehicle Care WARNING (Continued) 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 coolant is needed, add the proper mixture directly to the radiator, but be sure the cooling system is cool before this is done. How to Add Coolant to the Radiator { WARNING An electric engine cooling fan under the hood can start up even when the engine is not running and can cause injury. Keep hands, clothing, and tools away from any underhood electric fan. 1. Remove the pressure cap when the cooling system, including the pressure cap and upper radiator hose is no longer hot. Turn the pressure cap slowly counterclockwise. If a hiss is heard, wait for that to stop. A hiss means that there is still some pressure left. 2. Keep turning the pressure cap and remove it. { WARNING Steam and scalding liquids from a hot cooling system can blow out and burn you badly. (Continued)