Cadillac 2008 DTS Owner's Manual page 327

2. Then keep turning the cap and remove it.
5-32
3. Fill the coolant
surge tank with the
proper mixture to
the FULL COLD mark
on the side of the
coolant surge tank.
4.6L L37 Engine shown, 4.6L LD8 Engine similar
4. With the coolant surge tank 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 the FULL COLD mark
on the side of the coolant surge tank.
5. Then replace the cap. Be sure the cap is hand-tight
and fully seated.