Figure 2-12. Exhaust gas leakage into cooling system.

as 35 pounds per square inch (fig. 2-2). Pump pressures

are naturally greater at higher engine speeds and while the

thermostat is closed. The radiator pressure cap also

allows additional pressure to build up when the coolant is

boiling.

2-15.

Accessories Connected to Cooling System

a. Description. Many military vehicles have one or

more independent circulating systems connected by hose

or tubing to the engine cooling system for the purpose of

heating or cooling of oil coolers, air compressors,

transmissions, etc. The water pump circulates coolant to

radiators and water jackets of these accessories in the

same manner as to the vehicle radiator and engine water

jacket.

b. Effects of Leakage and Clogging. Leakage in

these units may affect cooling in the entire system either

through coolant shortage or by excessive coolant

Figure 2-12. Exhaust gas leakage into cooling system.

contamination, such as oil from the engine oil cooler. The

unit itself may be damaged by leakage, as in the case of

b. Prevention of Leakage. Considering the many

coolant leakage into a transmission. Restriction of coolant

possible points of leakage at the cylinder head joint and

flow in the connecting hose and tubes may also seriously

the seriousness of coolant leakage into the engine, it is

interfere with proper operation of such units.

imperative that the cylinder head always be kept perfectly

leakproof. Cylinder head bolts cannot be evenly tightened

c. Preventive Maintenance.

Cooling system

with an ordinary wrench. Use of a torque-indicating

preventive maintenance includes inspection of all special

wrench is necessary to obtain proper uniform pressure on

circulating systems to see that they are secure, leakproof,

all bolts and to avoid warpage of head or distortion of block

and in good condition.

at valve seats and cylinder bores from overtightening. The

extreme importance of maintaining cylinder head joint

2-16.

Cooling System Corrosion

tightness demands careful attention to all instructions on

installation of new gaskets, proper order for tightening

a. Rust Formation. A chemical combination of iron,

bolts, correct torque to apply, and rechecking torque

water, and air produces rust. The water jacket of the

following a new gasket installation. If any stud bolts are

automotive engine has a large mass of iron exposed to the

loosened in the block when removing cylinder head, they

cooling water, and no cooling system is free of air. Thus

should be tightened before head is installed.

all elements of rust formation are found in the cooling

system. Rust is a product of a chemical process called

2-14.

Engine Water Jacket

corrosion. Over 90 percent of the solid matter that clogs

radiators is rust. Corrosion not only produces harmful

The engine water jacket has many gasketed water joints

products like rust, but also damages iron and other cooling

and a number of metal water joints in both block and head,

system metals. When two different metals, such as iron

where preventive maintenance neglect may result in

and copper, are placed in contact with each other and then

leakage. Vibration, pressure, and wide changes in engine

immersed in water, a corrosive action called electrolysis

temperature, impose strains on all these points. Gaskets

takes place and electric currents flow through the water

deteriorate from effects of heat, water, and pressure.

from one metal to the other in exactly the same manner

Gasket joints at thermostat housing and water pump

that electricity is produced in a battery. Although these

mounting are common points of leakage. Metal joints,

currents are very weak, over a period of time they cause

such as core hole plugs, drain plugs, shut-off valves,

localized corrosion that weakens, pits, and sometimes

temperature gage fittings, and connections at water

eats completely

bypass or recirculation tubes, are all subject to leakage.

Corrosion leakage occasionally develops in metal water

joints. Any leakage at water jacket joints or casting cracks

is aggravated by pump pressures which may run as high

2-11