1999 GMC SIERRA radiator

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5-11
Cooling System (Gasoline Engine)
When you decide it's safe to lift the hood, here's what
you'll see:
A. Coolant Recovery Tank
B. Radiator Pressure Cap
C. Engine Fan(s)
CAUTION:
If your vehicle has air conditioning, the auxiliary
electric engine cooling 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 recovery tank is boiling,
don't do anything else until it cools down.

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The coolant level should be at or above the COLD mark.
If it isn't, you may have a leak in the radiator hoses,
heater hoses, radiator, water pump or somewhere else in
the cooling system.
CAUTION:
Heater and radiator hoses, and other engine
parts, can be very hot. Don't touch them.
If you do, you can be burned.
Don't run the engine if there is a leak. If you run
the engine, it could lose all coolant. That could
cause an engine fire, and you could be burned.
Get any leak fixed before you drive the vehicle.
NOTICE:
Engine damage from running your engine
without coolant isn't covered by your warranty.
NOTICE:
When adding coolant, it is important that you
use only DEX
-COOL
(silicate-free) coolant.
If coolant other than DEX-COOL is added
to the system, premature engine, heater core or
radiator corrosion may result. In addition, the
engine coolant will require change sooner
-- at
30,000 miles (50 000 km) or 24 months,
whichever occurs first. Damage caused by the
use of coolant other than DEX
-COOL
is not
covered by your new vehicle warranty.
If there seems to be no leak, start the engine again. See if
the engine cooling fan speed increases when idle speed is
doubled by pushing the accelerator pedal down. If it
doesn't, your vehicle needs service. Turn off the engine.

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5-13 How to Add Coolant to the Coolant
Recovery Tank (Gasoline Engines)
If you haven't found a problem yet, but the coolant level
isn't at or above the COLD mark, add a 50/50 mixture
of clean, drinkable water and DEX
-COOL
engine
coolant at the coolant recovery tank. (See ªEngine
Coolantº in the Index for more information.)
CAUTION:
Adding only plain water to your cooling system
can be dangerous. Plain water, or some other
liquid like alcohol, can boil before the proper
coolant mixture will. Your vehicle's coolant
warning system is set for the proper coolant
mixture. With plain water or the wrong mixture,
your engine could get too hot but you wouldn't
get the overheat warning. Your engine could
catch fire and you or others could be burned.
Use a 50/50 mixture of clean, drinkable water
and DEX
-COOL
coolant.
NOTICE:
In cold weather, water can freeze and crack the
engine, radiator, heater core and other parts.
Use the recommended coolant and the proper
coolant mixture.

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CAUTION:
You can be burned if you spill coolant on hot
engine parts. Coolant contains ethylene glycol
and it will burn if the engine parts are hot
enough. Don't spill coolant on a hot engine.
When the coolant in the coolant recovery tank is at or
above the COLD mark, start your vehicle.
If the overheat warning continues, there's one more
thing you can try. You can add the proper coolant
mixture directly to the radiator, but be sure the cooling
system is cool before you do it.

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CAUTION:
Steam and scalding liquids from a hot cooling
system can blow out and burn you badly. They
are under pressure, and if you turn the radiator
pressure cap
-- even a little -- they can come out
at high speed. Never turn the cap when the
cooling system, including the radiator pressure
cap, is hot. Wait for the cooling system and
radiator pressure cap to cool if you ever have to
turn the pressure cap.

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5-16 How to Add Coolant to the Radiator
1. You can remove the radiator pressure cap when the
cooling system, including the radiator pressure cap
and upper radiator hose, is no longer hot. Turn the
pressure cap slowly counterclockwise until it first
stops. (Don't press down while turning the
pressure cap.)
If you hear a hiss, wait for that to stop. A hiss means
there is still some pressure left.
2. Then keep turning the pressure cap, but now push
down as you turn it. Remove the pressure cap.

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3. Fill the radiator with the proper DEX-COOL

coolant mixture, up to the base of the filler neck.
(See ªEngine Coolantº in the Index for more
information about the proper coolant mixture.)
4. Then fill the coolant recovery tank to the
COLD mark.
5. Put the cap back on the coolant recovery tank, but
leave the radiator pressure cap off.

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6. Start the engine and let it run until you can feel the
upper radiator hose getting hot. Watch out for the
engine cooling fan(s).
7. By this time, the coolant level inside the radiator
filler neck may be lower. If the level is lower, add
more of the proper DEX
-COOL
coolant mixture
through the filler neck until the level reaches the
base of the filler neck.
8. Then replace the pressure cap. At any time during
this procedure if coolant begins to flow out of the
filler neck, reinstall the pressure cap. Be sure the
arrows on the pressure cap line up like this.