130
Main thermostat, checking
1.
Check to make sure the thermostat is fully closed.
To confirm this hold the thermostat up against a
light. No light may shine through where the joints
meet. If it does, this means that the thermostat can-
not be closed and must, therefore, be replaced.
2.
Heat the water to 75
°
C and insert the thermostat.
3.
After at least 30 seconds check to see if the ther-
mostat is still closed.
4.
Heat the water to boiling point (100
°
C). After the
water has been on the boil for at least 30 seconds,
check to see if the thermostat has opened at least
7 mm. If the thermostat has not opened, replace it.
Replacing main thermostat sealing
ring
Special tool:
(999) 6781 Drift
Use the special drift, 6781, to locate the sealing ring
properly in relation to the thermostat contact surface.
1.
Place the new sealing ring on drift 6781.
2.
Carefully tap in the sealing ring until the drift bot-
toms in the thermostat housing.
6781
Main thermostat
The thermostat housing contains two thermostats for
maintaining temperature in the engine cooling circuit
and one thermostat for the bus interior heating system.
If the bus does not have an hydraulic retarder or auto-
matic transmission with oil cooler, their connections 2
and 3 on the thermostat housing are inter-coupled with
a pipe elbow and the housing has only one vent hose.
The following is the flow in the thermostat housing:
1.
From engine
2.
To oil cooler in gearbox/retarder
3.
From oil cooler in gearbox/retarder
4.
To windscreen defroster and (if fitted) heated lube oil
tank
5.
To bus interior heating circuit
6.
To radiator
7.
To coolant pump
