Cooling System Descalers; Reverse Flushing; Spin-On Coolant Filter - PREVOST H3-41 Maintenance Manual

SECTION 05a: H3 SERIES COOLING SYSTEM
Fill with a 50/50-antifreeze/water solution
and add required inhibitors.
Vehicles with coolant filters:
Fill with a 50/50-antifreeze/water solution.
Replace coolant filter as per the Lubrication
and Servicing Schedule in section 24 if
required.
Dispose of spent fluids in an environmentally
responsible manner according to regulations in
effect in your area.
COOLING SYSTEM
(approximation)
Includes heating system: 24 US gal (91 liters)
8.1

COOLING SYSTEM DESCALERS

If the engine overheats and the fan belt tension,
coolant level and thermostat operation have
been found to be satisfactory, it may be
necessary to de-scale and flush the entire
cooling system.
Remove scale formation by using a reputable
and safe de-scaling solvent. Immediately after
using the de-scaling solvent, neutralize with a
neutralizing agent. It is important that product
directions be thoroughly read and followed.
After using the solvent and neutralizer, fully drain
the system, and then reverse flush the engine
and radiator (see "Reverse Flushing" in this
section) before filling the system with coolant
solution.
8.2

REVERSE FLUSHING

After the engine and radiator have been
thoroughly de-scaled, they should be reverse-
flushed. The water pump should be removed
and the radiator and engine reverse-flushed
separately to prevent dirt and scale deposits
from clogging the radiator tubes or being forced
through the pump.
accomplished by hot water, under pressure,
being forced through the cooling system in a
direction opposite to the normal flow of coolant,
loosening and forcing deposits out.
The radiator is reverse flushed as follows:
1. Remove the radiator inlet and outlet hoses
and replace existing radiator cap with a new
one.
2. Attach a hose to the top of the radiator to lead
water away from the engine.
PA1615 Maintenance Manual All Series | Section 05a revised September 2016
18
CAPACITY
Reverse flushing is
3. Attach a hose at the bottom of the radiator
and insert a flushing gun in the hose.
4. Connect the water hose of the gun to the
water outlet and the air hose to the
compressed air outlet.
5. Turn on the water and when the radiator is
full, turn on the air in short blasts, allowing the
radiator to fill between blasts.
NOTE
Apply air gradually. Do not exert more than
138 kPa (20 psi) air pressure. Too great a
pressure may rupture a radiator tube.
6. Continue flushing until only clean water is
expelled from the radiator.
The cylinder block and cylinder head water
passages are reverse flushed as follows:
1. Remove the thermostats and the water
pump.
2. Attach a hose to the water inlet of oil cooler
housing to drain water away from engine.
3. Attach a hose to the water outlet at the top of
the cylinder head (thermostat housing) and
insert the flushing gun in the hose.
4. Turn on the water until the jackets are filled,
and then turn on the air in short blasts. Allow
jackets to fill with water between air blasts.
5. Continue flushing until the water from the
engine runs clean.
If scale deposits in the radiator cannot be
removed by chemical cleaners or reverse
flushing as outlined above, it may be necessary
to remove the upper tank and rod out the
individual radiator tubes with flat steel rods.
Circulate the water through the radiator core
from the bottom to the top during this operation.
9

SPIN-ON COOLANT FILTER

The optional engine cooling system filter is used
to filter out impurities such as scale or sand from
the coolant and it also eliminates the process of
adding inhibitors to the antifreeze/water solution.
The filter is mounted onto the cooling fan drive
mechanism aluminum casting (Figure 17).
To replace a filter:
1. Close the filter shut-off valve on the filter
mounting head and unscrew the old filter
from mounting.