Engine thermostats principle and effects.

Engine thermostats perform three major functions

1.    Help an engine to reach operating temperature more quickly

2.    Help regulate engine temperature to prevent overheat

3.    Restrict flow to promote more even cooling

Most modern engines operate close to 200 degrees Fahrenheit. Below this operating temperature is considered cold and the engine needs more fuel to run properly. This is why it is desirable to reach operating temperature as quickly as possible.

Againg extra temperature is destructive for engine.So proper temperature is needed for economic operation.

 

When the engine is cold the thermostat blocks flow to the radiator and opens the bypass circuit. In this mode the water pump circulates coolant only inside the engine. The coolant is prevented from flowing through the radiator where it would be cooled.  Instead coolant flows through the bypass and back to the water pump. The effect is a quick increase in engine temperature.

The thermostat is basically a temperature controlled valve. The spring loaded valve is attached to a small cylinder filled with thermal wax. As the engine warms up, coolant transfers heat to the wax-filled cylinder. The heat causes the cylinder to expand and pushes down on the spring loaded valve.

 

If the temperature begins to fall below the limit set by the thermostat the flow will be restricted until it rises to the proper level. In a well maintained cooling system the thermostat will last for many years.

As coolant ages, the additives that prevent corrosion are depleted. This causes a huge amount of damage to the system and can cause thermostats to stick. If the thermostat sticks open, the engine runs too cold and waste fuel.

When a thermostat sticks closed the engine will overheat. Overheating causes cylinder heads to expand greatly. This has the effect of crushing the cylinder head gasket and can crack the head[s]. Pistons also expand and gall the cylinder walls. Overheating, even for a short while can severely damage the engine.

A non-working thermostat should be replaced with the exact temperature replacement specified for the vehicle. Removing the thermostat will NOT increase cooling. An engine without a thermostat will flow too much coolant to the front cylinders and may deprive coolant to the rear cylinders.

operating an engine without a thermostat can cause severe hot spots that may not show up on the temperature gauge. The sensor for the gauge measures temperature only in a small part of the engine. Rear cylinders could be severely overheating and not be revealed on the temperature gauge.