Engine thermostats are required to regulate the temperature of the engine during normal operation. The thermostat allows the engine to heat-up quickly when cold and maintain a desired temperature once the desired temperature has been reached.
The thermostat consists of a primary valve, secondary valve, springs and charge cylinder. The charge cylinder is full of a certain type of wax with a pre-defined melting point (the point at which the wax changes from solid to liquid). The wax changes state from solid to liquid at approximately 80°C in most engine cooling water systems.
After the change of state within the charge cylinder, the liquid occupies more space than when it was in a solid state. A rod inserted into the charge cylinder is pushed outwards linearly as there is now no longer space for the rod within the charge cylinder. The rod pushes the secondary valve closed whilst at the same time opening the primary valve. The temperature of the engine thus controls the movement of the rod and consequently the amount of cooling water sent to the radiator, or bypassing the radiator.
The thermostat has a proportional response design. The temperature of the engine dictates if cooling water is sent to the radiator, or, bypasses the radiator; this is effectively a feedback loop.
Hot cooling water temperature (>80°C) = Cooling water sent to radiator.
Cold cooling water temperature (<80°C)= Cooling water recirculated (radiator bypassed)
3D Model Details
This 3D model shows all major components associated with a typical thermostat, these include:
- Main Valve
- Air Bleed
- Charge Cylinder
- Secondary Spring
- Bypass Valve