PRIN. OF INTERNAL COMBUSTION ENGINES - OD1619 LESSON 2/TASK 3
(b) The pellet type thermostat (figure 71), is currently used because its
consists of a valve operated by a piston, a steel pin that fits into a small case
containing a copper impregnated wax pellet.
When the engine is cold, the wax
pellet is contracted and the spring pushes the valve closed.
The wax pellet
expands as the engine heats up, pushing the valve open against the force of the
spring. The pellet-type thermostat will maintain a constant temperature by varying
the size of the valve opening.