Buick 1994 Skylark Owner's Manual page 195

4. With the coolant surge tank pressure cap off, start the
engine and let it run yntil
you
can feel the upper
radiator hose getting hot. Watch out~'for the engine
fan.
By this time, the coolant level inside the coolant
surge tank may be lower. If the level is lower, add
more
of
the proper mix to the coolant surge tank
until the level reaches the split line formed by the
black and white
part
of the tank.
5. Then replace the
pressure cap. Be sure
the pressure cap is
tight.