Buick LaCrosse Owner's Manual page 356

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.
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.
The coolant surge tank pressure
cap can be removed when the
cooling system, including the surge
tank pressure cap and upper
radiator hose, is no longer hot.
1. Turn the pressure cap slowly
counterclockwise. If a hiss is
heard, wait for that to stop.
A hiss means there is still some
pressure left.
2. Keep turning the cap and
remove it.
3. Fill the coolant surge tank with
the proper mixture to the mark
pointed to on the front of the
coolant surge tank.