Pontiac 2006 G6 - Manual (Page 304)

2. Then keep turning the
pressure cap slowly,
and remove it.
3. Fill the coolant surge tank with the proper mixture,
to the FULL COLD mark. Wait about five minutes,
then check to see if the level is below the mark.
If the level is below the FULL COLD mark,
add additional coolant to bring the level up to the
mark. Repeat this procedure until the level remains
constant at the FULL COLD mark for at least
five minutes.
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 than
the FULL COLD mark, add more of the proper
mixture to the coolant surge tank until the level
reaches the FULL COLD mark.
5. Then replace the pressure cap. Be sure the
pressure cap is hand-tight and fully seated.
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