Specifications

20–01 Pressure Relief Cap
Check
WARNING
Do not remove or loosen the surge tank cap until
the engine and cooling system have completely
cooled. Use extreme care when removing the cap.
A sudden release of pressure from removing the
cap prior to the system cooling can result in a
surge of scalding coolant that could cause seri-
ous personal injury.
CAUTION
The radiator cap currently installed may not be the
same one installed when the vehicle was built. If
the radiator cap must be replaced, make sure that
it is the correct cap for the cooling system of the
vehicle. Because the radiator cap pressure rating
affects the operating temperature of the engine,
installing an improperly rated radiator cap may
have adverse effects on the cooling system, and
engine operating temperatures. This could cause
premature engine wear or damage.
1. Remove the fill cap first, to relieve the cooling
system pressure, then remove the SAE cap.
2. Using a radiator-cap tester, check the pressure
cap to see if it maintains pressure to within 10%
of the pressure rating marked on the cap. If it
doesn’t, replace the cap. See
Fig. 1 or Fig. 2.
Make sure that the replacement radiator cap is
correctly rated for the cooling system of the
vehicle.
3. There is a second valve in the radiator cap that
opens under vacuum. This prevents the collapse
of hoses and other parts that are not internally
supported when the system cools. Inspect the
vacuum-relief valve to be sure it is not stuck.
4. Make sure that the cap seals properly on the
coolant filler neck seat, and that the radiator cap
gasket is not damaged. On vehicles with screw
on caps with O-rings, make sure that the O-ring
is not cracked or deteriorated. Replace the cap if
the gasket shows deterioration or damage.
20–02 Radiator Pressure-
Flushing and Coolant
Change
NOTE: For additional instructions on cleaning
and flushing the engine’s cooling system, see
the applicable engine manufacturer’s mainte-
nance and operation manual.
1. Park the vehicle, apply the parking brakes. Tilt
the hood or cab. For instructions on tilting the
cab, see Group 60 of the
Century Class Trucks
Workshop Manual
.
2. Place a suitable container under the elbow of the
radiator outlet pipe and under the radiator. The
container should hold at least 60 quarts (58.6
liters) of fluid for single radiator applications, or
80 quarts (76 liters) for Argosy’s with auxiliary
radiators.
WARNING
Do not remove or loosen the surge tank cap until
the engine and cooling system have completely
cooled. Use extreme care when removing the cap.
A sudden release of pressure from removing the
cap prior to the system cooling can result in a
surge of scalding coolant that could cause seri-
ous personal injury.
3. Remove the surge tank cap.
4. On Argosy’s with auxiliary radiators, open the
remote bleed valve. See
Fig. 3.
WARNING
Do not attempt to drain the cooling system until
the coolant and engine are cool. Draining the
cooling system prior to the system cooling could
cause severe personal injury due to scalding.
5. Remove the drain plugs from the radiator side
tank, the lower tank on auxiliary radiators, and at
the lower radiator outlet pipe elbow, if equipped.
See
Fig. 4. Allow the coolant to drain.
6. Install and tighten the drain plug(s) and the ra-
diator outlet pipe drain plug after the radiator has
been drained. Do not overtighten the plugs.
7. Flush the radiator(s) as follows.
Engine Cooling/Radiator 20
Century Class Trucks Maintenance Manual, September 2010 20/1