1999 GMC C-SERIES engine

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6-21
Radiator Pressure Cap
(Gasoline Engines)
The radiator pressure cap
must be tightly installed
with the arrows on the cap
lined up with the top of the
overflow tube. This will
prevent coolant loss and
possible engine damage
from overheating.
When you replace your radiator pressure cap, an
ACDelco

cap is recommended.
NOTICE:
Your radiator pressure cap is a 9 psi (62kPa)
pressure
-type cap for use with medium duty
cooling systems only. It must be tightly installed
to prevent coolant loss and possible engine
damage from overheating. Be sure the arrows on
the cap line up with the top of the overflow tube.
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6-22
Surge Tank Pressure Cap
(Diesel Engines)
The surge tank pressure cap
must be tightly installed
with the arrows on the cap
lined up with the top tube of
the coolant surge tank.
When you replace your surge tank pressure cap, an
ACDelco

cap is recommended.
NOTICE:
Your surge tank pressure cap is a 9 psi (62kPa)
pressure
-type cap for use with medium duty
cooling systems only. It must be tightly installed
to prevent coolant loss and possible engine
damage from overheating. Be sure the arrows on
the cap line up with the top tube of the coolant
surge tank.
Thermostat
Engine coolant temperature is controlled by one or more
thermostats in the engine cooling system. The
thermostat stops the flow of coolant through the radiator
until the coolant reaches a preset temperature.
When you replace your thermostat, an ACDelco


thermostat is recommended for gasoline engines.
Caterpillar
parts are recommended for diesel engines.
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6-23
Engine Coolant (Gasoline Engine)
The cooling system in your vehicle is filled with
DEX
-COOL
engine coolant. This coolant is designed
to remain in your vehicle for 5 years or 150,000 miles
(240 000 km), whichever occurs first, if you add only
DEX
-COOL
extended life coolant.
The following explains your cooling system and how to
add coolant when it is low. If you have a problem with
engine overheating, see ªEngine Overheatingº in
the Index.
A 50/50 mixture of clean, drinkable water and
DEX
-COOL
coolant will:

Give freezing protection down to
-34F (-37C).

Give boiling protection up to 252F (122C).

Protect against rust and corrosion.

Help keep the proper engine temperature.

Let the warning lights and gages work as
they should.
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.
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6-24 What to Use
Use a mixture of one-half clean, drinkable water and
one
-half DEX-COOL
coolant which won't damage
aluminum parts. If you use this coolant mixture, you
don't need to add anything else.
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:
If you use an improper coolant mixture, your
engine could overheat and be badly damaged.
The repair cost wouldn't be covered by your
warranty. Too much water in the mixture can
freeze and crack the engine, radiator, heater core
and other parts.
If you have to add coolant more than four times a year,
have your dealer check your cooling system.
NOTICE:
If you use the proper coolant, you don't have to
add extra inhibitors or additives which claim to
improve the system. These can be harmful.
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6-25 Checking Coolant
Coolant Recovery Tank
(Gasoline Engines
-- Specialty Hood)
Coolant Recovery Tank
(Gasoline Engines
-- Sloped Hood)
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6-26
Surge Tank (Caterpillar
Diesel Engines)
When your engine is cold, the coolant level should be at
the COLD level, or a little higher, on the coolant
recovery tank with the gasoline engine, or at the COLD
FULL mark, visible through the surge tank, with the
diesel engine.
If this light comes on and
stays on, it means you're
low on engine coolant.
See ªLights, Low Coolant Warning Lightº in the Index
for further information.
Adding Coolant
If you need more coolant, add the proper DEX
-COOL

coolant mixture at the coolant recovery tank or the
surge tank.
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6-27
CAUTION:
Turning the radiator pressure cap (on a gasoline
engine) or the surge tank cap (on a diesel engine)
when the engine and radiator are hot can allow
steam and scalding liquids to blow out and burn
you badly. With the coolant recovery system, you
will almost never have to add coolant at the
radiator. Never turn the radiator pressure cap
or the surge tank pressure cap
-- even a
little
-- when the engine and radiator are hot.
Add coolant mixture at the recovery tank or the surge
tank, but be careful not to spill it.
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.
Some conditions, such as trapped air in the cooling
system, can affect the coolant level in the radiator. If you
need to add coolant to the radiator, follow the steps
listed under ªHow to Add Coolant to the Radiator.º
See ªEngine Overheatingº in the Index.
Engine Coolant
(Caterpillar
Diesel Engine)
If your vehicle has a Caterpillar diesel engine, see the
Caterpillar
Operation & Maintenance Manual provided
with your vehicle to find out what to add, also when and
how to service your cooling system.
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6-28
Power Steering Fluid
See your Maintenance Schedule for when to check your
power steering fluid.
How To Check Power Steering Fluid
Check your power steering fluid only when the engine is
warm. If the engine isn't warm, you probably won't get
an accurate reading.
Vehicles with diesel engines
have a sight glass. If you
can see fluid in the glass,
you have enough.Other models have a cap with a dipstick. If you have
one, unscrew the cap and check the dipstick. It should be
between ADD and FULL (if the engine is warm).
If you need to add some, put in only enough of the
correct fluid to bring the level up to the FULL mark (if
you have the dipstick) or so you can see fluid in the
glass, if you have a sight glass.
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