“Know your car” Series # 1


The Thermostat


Where is it? Follow the top radiator hose to where it joins the engine block. You will see a dome shaped alloy piece. That’s the thermostat housing. Inside is a thermostat. You will understand why its housing is that shape as you read through the article.

What does it do?
The thermostat is like a temperature operated gate. When the temperature of the coolant reaches 82°C the thermostat (gate) opens and lets the hot coolant flow out of the engine, via the top radiator hose, and into to the radiator.


When the engine is first started, and at low temperatures, the thermostat is completely closed and all of the coolant is kept recirculating through the engine. When the temperature of the coolant rises to between 82° and 92°C, the thermostat starts to open, allowing fluid to flow through the radiator. When the coolant reaches 93° - 104°C, the thermostat opens fully. The coolant then circulates through the hot engine block and passes to the radiator for cooling, and then back to the engine, via the lower radiator hose, and so on.


Source Diagram

The thermostat is fitted with the cylinder side in the engine (Techno’s rule) "cylinder side to the cylinder side".


How does it work? The "thermostat mechanism" is in the cylindrical part of the device. This cylinder is filled with a wax that begins to melt, and expand rapidly, at around 80°C. As the wax in the cylinder expands it pushes on a fixed rod from the top of the thermostat. The rod is fixed but the cylinder is mounted above a hole. As the cylindrical part moves down the valve opens up. The spring helps push the cylinder pack into place as the wax cools.



Safe journey


Rob (Techno) Spargo

Mazda MX-5 Club Victoria