Cadillac 2007 STS Owner's Manual page 391

Checking Coolant
The coolant surge tank and pressure cap are
located on the driver's side of the vehicle, toward
the rear of the engine compartment. See
Engine Compartment Overview on page 373 for
more information on location.
CAUTION:
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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/FROID line on the side of the
surge tank. Follow the arrow from the top of
the tank down the side to the horizontal mark.
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