The Thermostat and its Function

This section provides an overview of the thermostat's role in the engine cooling system, explaining how it helps the engine heat up quickly from a cold start and maintain its optimal operating temperature.

The Function of the Thermostat

• The thermostat is a component of the engine cooling system.

• It is a standard feature on all liquid-cooled piston engines.

• Its main function is to help the engine heat up quickly from a cold start and keep it at its optimal operating temperature.

• The thermostat can be placed close to either the cylinder block's coolant input or coolant outlet.

• When the coolant is still cool, the thermostat shuts off the longer circuit, closing the supply to the radiator.

• This causes the coolant to circulate within a shorter circuit, bypassing the radiator and allowing the engine to warm up faster.

• Once the desired temperature (typically 82 degrees Celsius) has been reached, the thermostat progressively opens the path through the radiator.

• This balances and maintains the optimal operating temperature for efficient engine performance.

• If insufficient mixing occurs between hot fluid from the shorter circuit and cold fluid from the longer circuit, and if temperatures continue to rise to 93 degrees Celsius, then only circulation within longer circuit occurs as shorter one shuts off.

• At this point, only circulation through radiator takes place.

How Does a Thermostat Work?

• A thermostat consists of a cylinder filled with wax that has a high coefficient of thermal expansion.

• Inside this cylinder are a rubber insert and a piston.

• When placed in hot liquid, as wax transitions from solid to liquid state, it expands significantly in volume and pushes the piston out of the cylinder.

• Modern automotive thermostats operate on this principle and can be adjusted to the desired opening temperature.

• The primary valve is mounted on the cylinder, and the assembly is placed in the thermostat frame secured in place within the thermostat housing.

• As the fluid within the system becomes hotter, the piston rests against the frame, causing the cylinder to move and open the primary valve.

• This enables circulation through radiator.

• When fluid (and wax) cools down, a spring helps return the valve to its closed position.

• A single-valve thermostat cannot shut off the shorter circuit.

• However, a double-valve thermostat uses two valves, with one shutting off the shorter circuit when longer circuit is fully open.

• The most common type of thermostat used is a double-valve thermostat.

Variations and Types of Thermostats

• Different vehicles use thermostats with different opening temperatures, which are usually indicated on them.

• Some thermostats feature a jiggle pin that plays a significant role in removing air locks in certain cars.

• Some engines with more complex cooling systems may have two thermostats to control temperature in multiple circuits.

• Modern automobiles may use electronically controlled thermostats for better temperature regulation.