Figure 2-2. Outside leakage of engine water jacket.

shock, and deterioration of gaskets, and wear, breakage,

hose usually takes place more rapidly from the inside (fig

or corrosion of metal parts may create leakage; these

2-3) so that outside inspection is not dependable.

conditions are often more severe in military operation.

Hardening of old hose increases the difficulty of keeping

The radiator pressure cap, which is used on nearly all

connections leakproof. Hose failures not only result in

military vehicles, creates additional pressure in the system,

leakage, but may also cause restriction of coolant

thereby increasing the leakage tendency at hose

circulation through clogging or collapsing.

Rubber

connections and other water joints. Radiator leakage may

particles from rotted hose linings will clog the radiator

be caused by accidental damage to the core from flying

water tubes and are very difficult to remove. Rotted hose

stones and debris, minor collisions with other vehicles or

may break open without warning and cause a large

objects, or from sabotage and combat damage. Such

coolant losses. In addition to the usual radiator hose,

damage can easily occur without the driver's knowledge.

some military vehicles have other coolant hose and tubes,

such as the cylinder head water by-pass and steam relief,

b. Appearance and Effects Small coolant leaks,

and overflow tank tubes. Frequent outside examination of

all hose and connections and careful inside inspection of

which show dampness or even dripping when cold, may

radiator hose whenever the connections are opened,

not be noticed when the engine is hot, due to rapid

require little time and can save much trouble

evaporation of the leakage.

Leakage of antifreeze

compound may be easier to find because It evaporates

much more slowly than water. Rusty or grayish-white

stains at joints in the radiator or engine water jacket (fig 2-

2) are usually indications of leakage, even though there

appears to be no dampness. Even small leaks should not

be neglected, since they often become larger, sometimes

suddenly, and generally while the vehicle is being driven.

When a driver neglects leakage inspection he risks

overheating during operation, possible mechanical

breakdown, and failure of his mission.

Figure 2-3. Inside deterioration and clogging of rubber

hose.

2-7.

Thermostat

a. Causes of Failure The function and operation of

the thermostat is such that this indispensable unit does not

have an indefinite service life and can fail with little or no

advance warning. The valve and operating mechanism Is

subjected to extreme temperature changes, corrosion, and

also to wear and bending movement. Rust or foreign

Figure 2-2. Outside leakage of engine water jacket.

matter in the coolant interferes with proper thermostat

operation and overheating from any cause may damage it.

2-6.

Rubber Hose

Defective thermostats may stick open or closed, or they

may leak. Thermostat Testers (1, fig 2-1) are available

Leaks are more common at radiator hose connections

and will prove to be a time-saver. To test, remove the

than anywhere else In the cooling system.

Engine

thermostat from the vehicle. Place thermostat in tester,

vibration has a tendency to wear and loosen rubber hose

allow to heat and read the thermostat opening

connections. Clamps may buckle the hose and threads on

temperature.

the clamp bolt are sometimes stripped. The hose itself

has a limited service life. Heat and water cause hose

swelling, hardening, cracking, and rotting. Deterioration of

2-5