Cadillac 2003 CTS Owner's Manual page 309

How to Add Coolant to the Coolant
Surge Tank
If you haven't found a problem yet, check to see if
coolant is visible in the surge tank. If coolant is visible
but the coolant level isn't at the FULL COLD/FROID
line on the side of the coolant surge tank, add a 50/50
mixture of clean, drinkable water and DEX
coolant at the coolant surge tank, but be sure the cooling
system, including the coolant surge tank pressure cap, is
cool before you do it. See "Engine Coolant" in the Index
for more information.
If no coolant is visible in the surge tank, add coolant
as follows:
CAUTION:
Steam and scalding liquids from a hot cooling
system can blow out and burn you badly. They
are under pressure, and if you turn the coolant
surge tank pressure cap
can come out at high speed.
5-14
R
-
COOL
-- --
even a little they
CAUTION: (Continued)
CAUTION: (Continued)
Never turn the cap when the cooling system,
including the coolant surge tank pressure cap, is
hot. Wait for the cooling system and coolant
surge tank pressure cap to cool if you ever have
to turn the pressure cap.