Cadillac 2017 CT6 Owner's Manual page 260

Caution
If improper coolant mixture,
inhibitors, or additives are used in
the vehicle cooling system, the
engine could overheat and be
damaged. Too much water in the
mixture can freeze and crack
engine cooling parts. The repairs
would not be covered by the
vehicle warranty. Use only the
proper mixture of engine coolant
for the cooling system. See
Recommended Fluids and
Lubricants 0 321.
Never dispose of engine coolant by
putting it in the trash, pouring it on
the ground, or into sewers, streams,
or bodies of water. Have the coolant
changed by an authorized service
center, familiar with legal
requirements regarding used
coolant disposal. This will help
protect the environment and your
health.
Checking Coolant
The vehicle must be on a level
surface when checking the coolant
level.
3.0L V6 Engine Coolant
Surge Tank
Vehicle Care
3.6L V6 Engine Coolant
Surge Tank
Check to see if coolant is visible in
the coolant surge tank. If the coolant
inside the coolant surge tank is
boiling, do not do anything else until
it cools down. If coolant is visible
but the coolant level mark is not
visible, add a 50/50 mixture of
clean, drinkable water and
DEX-COOL coolant at the coolant
surge tank to the top rib on the
middle of the tank, but be sure the
cooling system is cool before this is
done. See Engine
Overheating 0 261.
259