Testing Radiator Caps

NOTE

After all leaks have been repaired, the radiator should be

painted. A non-insulating paint should be used. Before

The appearance of air bubbles in thermostat

painting, the radiator should be clean, dry and free of all

housing will indicate a leak.

flux residue.

(6) Repeat procedure on all cylinders until all

leaks are located.

NOTE

(7) When air pressure-hissing indicates the

cylinder valves are open, the engine should be rotated until

No more than one coat of paint will be applied to

valves are closed.

radiator cores on tactical wheel vehicles (3/4 ton

c. Testing with Automatic Transmission. This test

through 10 ton trucks), except M39A2 series

trucks, which will not be painted.

should be performed with engine cold. As engine-heats,

water expansion could result in appearance of bubbles

when there is no leak. This test will not locate the leak but

3-24.

Testing Stand

only determine if a leak exists.

(1) Disconnect fan belt from water pump.

The radiator test and repair stand (8, fig. 2-1) combines

(2) Remove thermostat and fill thermostat

leak test tank, work bench and soldering equipment into

opening with water.

one efficient unit It has a motor driven work bench rack for

(3) Operate engine for a short time and

raising and lowering the radiator at the test tank with

observe for air bubbles in thermostat housing while engine

minimum effort. When the rack is elevated above the tank

is running.

water, it becomes a sturdy adjustable work bench.

d. Combustion Leak Tester. For combustion leak

Soldering torch, air blow gun and regulated air connections

testing, a Combustion Leak Tester (5, fig 2-1) is also

are built in. Specially designed jigs for supporting the

recommended. This tester can be used on all types of

radiator in any position are attached to the unit. This well-

vehicles and operates on a chemical color change

designed arrangement promotes an organized systematic

indication It requires only the removal of the radiator cap

repair procedure with a saving of time and effort.

and will locate the leak with the removal of each spark

plug wire in sequence.

3-25.

Field Test Tank

3-22.

Testing Radiator Caps

For field service a collapsible canvas tank (fig 3-9) will be

provided in the third echelon equipment unit set No 1 for

Radiator caps should be tested periodically for proper

light maintenance companies. This tank consists of a one-

operation. A defective cap can cause loss of coolant,

piece canvas bag with wooden staves in pockets to hold

over-pressure damage or collapse of cooling system

the sides up and four round poles running through canvas

components. When testing radiator caps, the pressure

loops to support the rim. A rubber mat protects the bottom

seal on both the cap seating surface and the radiator filler

of the tank from being torn by the radiator. When the tank

neck should be carefully inspected. A cooling system

is collapsed, two poles are removed and placed inside the

tester (2, fig 2-1) should be used. These testers make use

tank, which is then rolled inside the mat and fastened with

of a hand pump, a pressure gauge and adapter fittings for

five flat metal hooks

attaching to the various types of caps. The radiator cap

seals should be moistened to assure that the test results

are equal to operating conditions. To determine the

pressure relief valve opening pressure, the manufacturer's

specifications should be consulted In some instances, the

pressure is stamped on the cap. Be sure that the cap

operates at the specified pressure.

The vacuum

protection valve can be tested by visually checking that the

valve spring operates and the seal is good.

3-23.

Cleaning and Painting

CAUTION

Radiators should never be painted with ordinary

lacquers, enamels or paints as these insulate the

heat transfer. This reduces the cooling efficiency.

Figure 3-9. Collapsible canvas tank.

Always use Non-Insulating Radiator Core Paint.

3-9