GMC 2010 Sierra Owner's Manual page 498

3. Fill the coolant surge tank with the proper mixture
to the FULL COLD mark.
4. With the coolant surge tank pressure cap off, start
the engine and let it run until the engine coolant
temperature gauge indicates approximately
195°F (90°C).
6-38
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 FULL COLD mark.
5. Replace the pressure cap. Be sure the pressure
cap is hand-tight and fully seated.
6. Verify coolant level after engine is shut off and the
coolant is cold. If necessary, repeat coolant fill
procedure Steps 1 through 6.
Notice: If the pressure cap is not tightly installed,
coolant loss and possible engine damage may
occur. Be sure the cap is properly and tightly
secured.