Chevrolet 2007 Cobalt Owner's Manual page 298

Checking Coolant
The coolant surge tank is located in the engine
compartment on the driver's side of the vehicle.
See Engine Compartment Overview on page 284
for more information on location.
298
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 COLD FILL line.