Level one thermostat control

1. Gloucestershire College
Motor Vehicle Studies.

2. Engine Cooling Systems
This presentation will explore:
• Thermostat Control

3. The Thermostat
Closes when cold
valve
jiggle pin
thrust pin
wax capsule
rubber membrane

4. The Thermostat
Opens when hot
Wax expands to force the pin out,
pushing down the capsule.
Allows the coolant to circulate.

7. Thermostat Location

8. Thermostat Closed
When the engine is cold, the thermostat
is closed. A return spring holds the
diaphragm against the aperture.
The route to the radiator via the top
hose is cut off by the closed thermostat.
This accelerates the engine warm-up
process to both reduce engine wear
and emissions.
By-pass open
To top hose
and radiator
A by-pass channel returns the coolant
to the water pump and allows it to
circulate through the water jacket in
the engine block and head. This cycle
repeats until the optimum engine
temperature is reached.

9. Thermostat Open
Coolant is allowed through to the
radiator and then back to the
engine. This continuing process
allows the engine temperature to
be maintained at its optimum
value, and the thermostat will
continue to cycle as temperatures
rise and fall.
As the engine and coolant warms
up, a wax-filled pellet expands in
the thermostat and pushes the
thermostat open, closing the
by-pass port.
To top
hole
By-pass closed
To top hose
and radiator

10. Thermostat

11. Experiment.
• By carrying out a simple experiment we
can simulate a thermostat located in a
engine and check its operation.
• WARNING! –The Water in the Kettle is
Boiling. Go Careful!