Figure 2-6. Radiator leakage.

2-11.

Radiator Overflow Tank

a. Function The radiator overflow tank serves as

temporary reservoir for coolant overflowing from the

radiator while driving, or Immediately after the engine is

stopped. Any coolant collected in the tank is forced back

into the radiator when the engine cools down and creates

a vacuum in the cooling system (para 1-9)(fig 1-6).

b. Causes of Failure. Like the radiator cap, the

overflow tank is exposed to corrosive effects of steam and

air. Being empty most of the time, it receives little

protection from rust inhibitors in the coolant. Thin-walled

steel overflow tanks may therefore rust through from the

inside and allow coolant overflow to leak out and become

lost. Water, condensed in the tube connecting pith

radiator, may freeze or the tube may become clogged with

foreign matter.

c. Effects of Failure. An air leak in tank-to-radiator

tube or above liquid level in the radiator can cause failure

of the vacuum and prevent coolant in tank from returning

to the radiator. In fact, a liquid or air leak anywhere in the

cooling system will make overflow tank operation less

effective. Clogging of connecting tube not only puts tank

out of service but also seals the system, creating the

possibility of harmful pressures.

d. Prevention of Failure. Proper functioning of

overflow tank depends on maintaining an airtight cooling

system, and free unobstructed flow between tank and

radiator. This requires frequent inspection for coolant

leakage, for air leaks above coolant level, for connecting

tube clogging, and for presence of coolant in overflow tank

Figure 2-6. Radiator leakage.

with engine cold.

b. Air Passage Obstruction. The primary function of

2-12.

Water Pump

the radiator is to transfer heat efficiently from the coolant

to the air (para 1-9d). This is not possible without clean,

a. Pumping Failure The water pump is the only

straight air fins and unobstructed air passages. Flying

power-driven unit in the coolant system. Pumping failures

dust, sand, grass, leaves, and other debris may clog air

are most often caused by broken or loose drive belts, but

passages in a very short time. Air fins are easily bent and

edge wear of impeller blades and wear of pump housing

damaged by impact of small stones and from other

also reduce pumping capacity. Sand, rust, and other

accidental causes. The problem of maintaining sufficient

abrasive foreign matter in coolant have a tendency to clear

air flow through the radiator is often further complicated by

areas impeller blades. Corrosion of impeller (fig 2-7) and

brush guards, air inlet screens, shutters, armor, etc.

housing may result from failure to install corrosion inhibitor

Therefore, constant attention to the condition of all air

with water, or to discard rusts antifreeze solution.

passages and restrictions is required in order to avoid the

danger of overheating. In extreme cases, cleaning may be

required at least daily.

2-8