TOPIC 4. THERMOSTAT

TM 10-3930-644-14&P

TOPIC 4. THERMOSTAT

A. DESCRIPTION The thermostat is Installed in the

6. Suspend

and

completely

immerse

the

cooling system to regulate the temperature of the

thermostat in a container of clean water (Figure

coolant, and is located in the water outlet elbow.

4-1). Heat the water and stir with an accurate

Normally, when the coolant temperature is 180F or less,

thermometer to check the water temperature.

the thermostat is closed, preventing the coolant from

flowing through the radiator.

When the coolant

7. As the water temperature reaches 180F,

temperature rises above 180F, the thermostat begins to

observe the thermostat. If the valve does not

open, allowing the coolant to flow through the radiator

start to open at temperatures of 180-200F. or

where the temperature is reduced through the cooling

if it opens well before the 180 point is reached

effect of the fan.

the thermostat should be replaced.

The thermostat should be fully open at 202F; in this

manner, it acts as a temperature controlled valve that

regulates

the

coolant

temperature

within

its

characteristic limits.

The thermostat seldom needs replacement in service,

however, it should be checked when the cooling system

is cleaned. While removing the thermostat, check the

hose; if it shows signs of deterioration when flexed,

replace the hose. Also check the hose connected to the

bottom of the radiator, and if it shows signs of

deterioration, replace it.

CAUTION

D0 NOT RUN ENGINE WITHOUT A

THERMOSTAT!

B. REMOVAL

Figure 4-1. Testing Thermostat

1. Replace the thermostat if it sticks in an open or

closed position. If the engine overheats or does

not reach and maintain normal operating

temperature, the thermostat should be removed,

tested for proper operation, and replaced if

found defective.

2. Remove the engine side panels and raise the

operator's seat.

3.Partially drain the cooling system, then remove the

clamps from the top radiator hose and the

coolant by-pass hose or L.P.G. converter tube.

Pull these hoses off the water outlet elbow.

4. Remove two nuts and lockwashers, and lift the

outlet elbow off the cylinder head. Remove

Figure 4-2. Replacing Thermostat

adapter ring and thermostat from elbow.

5. Before testing thermostat, clean the bellows and

examine for rupture or distortion. If the valve

can be pulled or pushed off its seat with only a

slight effort when cold, or if valve does not seat

properly, the unit is defective and must be

replaced

M-155-1

2-45