Flushing; Cooling System Descalers - PREVOST H3-41 Maintenance Manual

SECTION 05A: H3 SERIES COOLING SYSTEM
NOTE
If for any reason, the coolant level drops
below the surge tank level probe, the Check
Engine warning light will illuminate.
5. Stop engine and allow cooling.
6. Open the two heater line shutoff valves,
check the coolant level in the surge tank,
and then add as required.
CAUTION
Never pour cold coolant into a hot engine.
The sudden change in temperature may crack
the cylinder head or block.
If the entire system has been drained, redo the
previous steps while maintaining the two heater
line shutoff valves in the "Open" position. With
engine running, activate the driver's and central
heating systems to permit coolant circulation. If
the vehicle is equipped with a windshield upper
section defroster, momentarily pinch the hose
located between the recirculating pump suction
and the defroster outlet connector to ensure
windshield upper section defroster complete
filling. Complete the procedure by bleeding the
heater cores as explained in Section 22, under
"9.4 Bleeding Heating System".
9

FLUSHING

If the cooling system is contaminated, flush the
cooling system as follows:
1. Drain the coolant from the engine.
2. Refill with clean water.
CAUTION
If the engine is hot, fill slowly to prevent rapid
cooling and distortion of the engine castings.
3. To thoroughly circulate the water, start and
run the engine for 15 minutes after the
thermostats have opened.
4. Fully drain system.
5. Refill with clean water and operate for 15
minutes after the thermostats have opened.
6. Stop engine and allow cooling.
7. Fully drain system.
Vehicles without coolant filters:
18 PA1621 Maintenance Manual All Series | January 2017
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: 27 US gal (102
liters)
9.1

COOLING SYSTEM DESCALERS

If the engine overheats and the water pump,
coolant level and thermostat operation have
been found to be satisfactory, it may be
necessary to flush and de-scale the cooling
system.
1. Drain the coolant from the engine.
2. Fill system with clean water.
3. Add the required amount of a reputable
commercially available de-scaling product
(aluminum & copper compatible). It is
important that product
thoroughly read and followed regarding
duration of the treatment, temperature and
product mix ratio).
CAUTION
Only use de-scaling products sold by a
reputable manufacturer, product must be
aluminum and copper compatible and must
be safe for rubber hoses and gaskets.
Some de-scaling products will require the use
of a neutralizing agent before coolant system
refill
Carefully follow manufacturer's directions to
avoid cooling system damage when using
descaling products.
Never use "home brewed" descaling solution
containing caustic or acid products not
intended for cooling system descaling or
having unknown active product concentration.
CAPACITY
directions be