GMC 2007 Sierra 1500 Pickup Owner's Manual page 504

Checking Coolant
The coolant surge tank is located in the engine
compartment on the passenger's side of the
vehicle. See Engine Compartment Overview on
page 480 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.
504
The vehicle must be on a level surface. When
your engine is cold, the coolant level should be at
the FULL COLD mark.
If your vehicle is equipped with a low coolant
sensor and the LOW COOLANT LEVEL message
comes on and stays on, it means you are low
on engine coolant. See "LOW COOLANT LEVEL"
under DIC Warnings and Messages on page 270.