LEAKAGE TESTS

TM 10-3930-623-12

5-21. Cleaning Radiator. Clean the radiator cap by

hose. Add water to level of housing outlet. Disconnect

spraying a stream of water (hot, if possible) through the

drive belt from fan and water pump pulley. Start engine,

holes in the valve cage while moving the valve up and

accelerate several times and watch for bubbles in

down with a pencil or a blunt wooden instrument. Clean

thermostat housing. The appearance of bubbles or the

out dirt, trash and insects imbedded in the air passages

sudden rise of liquid when accelerating is evidence of

of the radiator, using compressed air or a stream of

head gasket leakage into cooling system. Make test

water. Do not use steam.

quickly before coolant reaches boiling point as steam will

give misleading results.

Correct the condition by

replacing cylinder head gasket and repeat test. If

CAUTION

leakage is still evident, a cracked cylinder head,

requiring replacement, is indicated. Install thermostat;

Do not hold air or water hose too

and connect radiator hose. Fill radiator. Install and

close to radiator or use too great a

adjust fan and alternator drive belt.

pressure as damage to the radiator

may result. Clean out any stoppage

NOTE

in drain cocks with a soft wire.

The cooling system must be free of

5-22. Filling System. Close radiator and cylinder block

rust and scale to maintain efficiency

drain cocks. Fill system to suit climate conditions as

of the system. The use of corrosion

follows:

If the prevailing temperature is above 32

inhibitor

compound

reduces

degrees F, partially fill the system with clean, fresh

corrosion and formation of scale.

water. Add corrosion inhibitor compound and fill system

inhibitors are not cleaners and do not

with water until coolant is evident at radiator opening. If

remove rust or scale already formed.

there is a possibility that temperatures below 32 degrees

Treating the cooling system with the

F will be encountered, add anti-freeze as required to

inhibitor consists of adding the

compound to the coolant.

The

safeguard cooling system from freezing at lowest

inhibitor

should

renewed

expected temperature. Fill with coolant to level of filler

periodically, especially if the system

neck, install radiator cap, start engine and operate at fast

has been cleaned or flushed.

idle until temperature gage shows normal operating

temperature. Stop engine and check coolant level. Add

5-26. FAN BELT ADJUSTMENT (fig. 6-8). Loosen

coolant, if necessary.

capscrew attaching idler pulley mounting bracket to

slotted adjusting arm bracket.

Loosen capscrew

5-23. LEAKAGE TESTS. Air in the cooling system or

attaching idler pulley bracket to adjusting arm and move

exhaust gas leaking into the system causes rapid

idler pulley either way to obtain correct belt tension. A

corrosion and rust formations which will eventually clog

light pressure applied to belt midway between fan pulley

the system and cause overheating and loss of coolant.

and water pump must produce a 3/4 to 1 inch belt

deflection. When properly adjusted, tighten capscrew

Air may be drawn into the system due to low liquid level

attaching bracket to arm.

in the radiator, leaky water pump or loose fittings.

Exhaust may be blown into the coolant system, past the

5-27. ELECTRICAL SYSTEM MAINTENANCE.

cylinder head gasket or through cracks in the cylinder

head and crankcase.

5-28. IGNITION TIMING. Timing the ignition system so

the spark occurs at each plug at the correct point in

5-24. Air Suction Test. Completely fill radiator with

piston travel may be done by either of two methods: (a)

coolant. Drain out one and one-half pints of coolant to

using a spark plug triggered timing light with the engine

prevent overflow during test. Be sure radiator cap is in

running, or; (b) static timing, with the engine not running.

Either method requires observation of a timing mark on

good condition and will make an air-tight seal. Attach a

the flywheel through an observation hole in the top of

length of rubber tubing to the end of the overflow tube,

flywheel housing (see figure 1-2).

being certain the connection is air-tight. Operate engine

until temperature gage stops rising and remains

5-29. USING TIMING LIGHT.

stationary. Without changing engine speed, put end of

rubber tube in bottle of water. Be sure there are no

1. Connect timing light according to the specific

kinks or sharp bends to restrict air flow. Watch for air

instructions for the timing light being used. Timing light

bubbles in the water as an indication that air is entering

lead to spark plug may be connected to either number 1

the cooling system. Correct the condition by tightening

or number 6 spark plug. Remove cover from timing

cylinder head bolts, water pump mounting bolts, hose

mark hole (see figure 1-2).

clamps and all fittings. Replace all hose that is cracked,

2. Start engine and run it at slow idle speed (400 rpm

swollen or otherwise deteriorated.

or less). Direct flash from timing light into hole in top of

flywheel housing (see figure 1-2) to light timing mark

5-25. Head Gasket Leakage Test. Start test with a cold

each time it passes hole. Mark will appear to stand still

engine.

Remove thermostat housing and reinstall

although engine is running. Shade area if needed to

thermostat housing without thermostat or water outlet

increase visibility.

5-4