Cooling System - GMC 2005 T-Series Owner's Manual

If you no longer have the overheat warning, you can
drive. Just to be safe, drive slower for about 10 minutes.
If the warning does not come back on, you can drive
normally.
If the warning continues and you have not stopped, pull
over, stop, and park your vehicle right away.
If there is still no sign of steam, you can push down the
accelerator until the engine speed is about twice as
fast as normal idle speed for at least three minutes while
you are parked. If you still have the warning, turn off
the engine and get everyone out of the vehicle until it
cools down.
You may decide not to lift the hood but to get service
help right away.
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Cooling System

CAUTION:
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If your vehicle has air conditioning, the
auxiliary electric fan under the hood can start
up even when the engine is not running and
can injure you. Keep hands, clothing and tools
away from any underhood electric fan.
If the coolant inside the coolant surge tank is boiling, do
not do anything else until it cools down. The vehicle
should be parked on a level surface.
When the engine is cold, the coolant level should be at
the COLD FULL mark. If it is not, you may have a
leak at the pressure cap or in the radiator hoses, heater
hoses, radiator, water pump or somewhere else in
the cooling system.