Pontiac 2005 Bonneville Owner's Manual page 311

3. Fill the coolant surge tank with the proper mixture
to the full cold fill mark on the side of the coolant
surge tank.
4. With the coolant surge tank pressure cap off, start
the engine and let it run until you can feel the upper
radiator hose getting hot. Watch out for the
engine cooling fans.
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 about 4.5 inches (11.4 cm)
from the top of the filler neck.
5. Then replace the pressure cap. Be sure the arrow
on the pressure cap lines up with the tube.
5-51