Buick 2010 Lacrosse Owner's Manual page 303

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. Then 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.
4. With the coolant surge tank cap
off, start the engine and let it run
until the upper radiator hose
starts getting hot. Watch out for
the engine cooling fan(s). By this
time, the coolant level inside the
coolant surge tank may be
lower. If the level is lower, add
more of the proper mixture to
the coolant surge tank until the
level reaches the mark pointed
to on the front of the coolant
surge tank.
5. Replace the cap. Be sure the
cap is hand tight and full
seated.
If coolant is needed, add the proper
®
DEX-COOL coolant mixture at the
coolant recovery tank.