Cadillac 2007 DTS Owner's Manual page 368

Checking Coolant
For more information on location, see Engine
Compartment Overview on page 356.
368
The engine coolant
surge tank is located
toward the rear of
the engine compartment
on the passenger's
side of the vehicle.
CAUTION:
{
Turning the surge tank pressure cap when
the engine and radiator are hot can allow
steam and scalding liquids to blow out
and burn you badly. Never turn the surge
tank pressure cap — even a little — when
the engine and radiator are hot.
The vehicle must be on a level surface. When
your engine is cold, the coolant level should be
at the FULL COLD mark, located on the side of
the surge tank that faces the engine.