GMC Sierra Denali 2009 Owner's Manual page 369

Checking Coolant
The vehicle must be on a level surface when checking
the coolant level.
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 is not at or above
the FULL COLD mark, add a 50/50 mixture of clean,
drinkable water and DEX-COOL
surge tank, but be sure the cooling system is cool
before this is done.
®
coolant at the coolant
The coolant surge tank is located in the engine
compartment on the passenger side of the vehicle. See
Engine Compartment Overview on page 5-14 for
more information on location.
The coolant level should be at or above the FULL
COLD mark. If it is not, you may have a leak in the
cooling system.
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