MOTOR TRUCK SERVICE MANUAL
COOLING SYSTEM
GENERAL
TROUBLE SHOOTING
gasket, leaky radiator hose or water pump seal. Foam is
Causes of Coolant Loss:
an excellent insulator and can seriously interfere with
1. Leaks and seepage - may be either external or
proper circulation.
internal.
5. Evaporation - Evaporation reduces the amount
of coolant in the system. This is a common
External leaks easy to locate, may occur at radiator,
occurance where alcohol base types of
heater, water pump, core plug hole, hose connections,
antifreeze are used. A faulty pressure cap may
radiator cap, drain cocks, and gaskets.
also be the cause of evaporation.
Internal leaks are more difficult to locate since these
Cause of Overheating:
leaks occur at cracks and faulty head gaskets.
1. Cooling System
Internal leaks are indicated by a decrease in coolant
a. Low coolant supply
level and the presence of coolant in crankcase. Correct
b. Leaks at any of the following: gaskets,
this condition immediately or serious damage to engine
hose connections, water pump, radiator,
will result.
heater, core plugs, drain cock or plugs,
2. Boiling - may be caused by any of the following:
a. Radiator or other parts of cooling system
cracked head or block.
clogged with rust or scale.
c. Broken or loose fan belt.
b. Grille or bug screen clogged.
d. Radiator clogged.
c. Radiator core fins damaged.
e. Collapsed or clogged hose.
d. Thermostat defective stuck closed.
f. Defective pressure cap.
e. Water pump leaking air into system.
g. Worn or corroded impeller on water pump.
f. Radiator hose collapsed or rotting inwar
h. Foaming.
dly.
i. Radiator air flow obstructed.
g. Radiator pressure cap defective.
j. Bent fan blade.
h. Cylinder head loose causing exhaust gas
k. Improper or defective thermostat.
leakage into cooling system.
2. Ignition System
a. Ignition timing late.
i. Water pump impeller corroded or loose on
b. Defective spark advance.
shaft.
3. Fuel System
j. Antifreeze protection inadequate causing
a. Carburetor set too lean.
partial freeze-up.
b. Valves timed late or leaking.
3. After-Boil - Boiling which may occur in a cooling
system after the engine is shut off even though it
c. Intake manifold leaking.
did not occur during operation is known as
d. Leak in vacuum operated accessories.
afterboil. This condition which usually happens
4. Miscellaneous
a. Clogged muffler or tail pipe.
to cooling systems that need attention, occurs
b. Stiff rebuilt engine.
because the coolant is still picking up heat from
c. Dragging brakes.
the engine and the heat is not being dispersed
d. Low engine oil level.
by circulation through the radiator. Other causes
e. Engine overloaded.
of afterboil are overprotection or use of high
Cause of Overcooling:
temperature thermostat with alcohol type
1. Missing thermostat.
antifreeze,
improper
installation
of
the
2. Defective thermostat stuck open.
thermostat, or a thermostat that is operating
3. Short runs and intermittent driving.
improperly.
4. Foaming - Foaming of coolant may also cause
coolant loss. This occurs only with a very dirty
cooling system and under severe operating
conditions. Usually an air or exhaust leak in the
system contributes to foaming and this is caused
by a faulty
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