20–01 Radiator Cap Checking
WARNING
Drain the coolant only when the coolant and en-
gine are cool. Draining it when these are hot could
cause severe personal injury due to scalding.
The radiator cap is the most often ignored part in the
cooling system. If it is suspect, replace it. An inspec-
tion means checking the cap with a pressure tester.
A radiator cap in good condition will not open below
9 psi (62 kPa). A visual check is also in order: look
for signs of deterioration of the inner gasket. Also
look for cracks or breaks in the spring retainer in the
cap, and for corrosion or deposits on the spring itself.
If the spring is not in perfect condition, it has prob-
ably lost tension; replace it.
20–02 Radiator Pressure
Flushing and Coolant
Changing
NOTE: For additional instructions on cleaning
and flushing the cooling system, see the engine
manufacturer’s maintenance and operation
manual.
WARNING
Drain the coolant only when the coolant and en-
gine are cool. Draining it when these are hot could
cause severe personal injury due to scalding.
1.
Drain the radiator.
1.1
Remove the surge tank cap.
1.2
Remove the plug at the bottom of the ra-
diator left side tank to drain the engine
coolant.
2.
Disconnect the radiator inlet and outlet hose con-
nections.
3.
Flush the radiator.
3.1
Attach a flushing gun nozzle to the radia-
tor outlet.
3.2
Run water in until the radiator is full.
3.3
Apply no more than 20 psi (138 kPa) air
pressure intermittently to help dislodge
sediment buildup in the core.
CAUTION
When flushing the radiator, do not apply more
than 20 psi (138 kPa) air pressure. Excessive pres-
sure can damage the radiator or heater core.
4.
Drain the radiator, and flush the radiator until
clean water flows from the radiator. Remove the
flushing gun.
5.
Close the petcock at the bottom of the radiator.
6.
Connect the hoses. When you install Breeze
Constant-Torque hose clamps, the clamps must
be tightened to the correct torque. The screw tip
of the clamp must extend about 1/4 inch (6 mm)
from the clamp housing, and the belleville
washer stacks must be collapsed almost flat.
See
. You must use a torque wrench to
install these hose clamps correctly. The correct
installation torque for Breeze Constant-Torque
hose clamps is as follows:
For clamps with a 5/16-inch tightening screw
hex:
40 lbf·in (460 N·cm).
For clamps with a 3/8-inch tightening screw hex:
90 lbf·in (1020 N·cm).
NOTE: All hose clamps will lose torque after
installation due to "compression set." However,
when correctly installed, Breeze Constant-
08/15/94
f200286
A
B
1
A. The screw tip must extend about 1/4 inch (6 mm).
B. The belleville washer stacks must be collapsed
almost flat.
1.
Tightening Screw Hex
Fig. 1, Breeze Constant-Torque Hose Clamp
Engine Cooling/Radiator
20
School Bus Chassis Maintenance Manual, March 2003
20/1
