Checking the Thermostat (Mazda 121 (3))

The thermostat opens the coolant passage to the radiator when the engine warms up. If the thermostat remains closed due to a fault, the engine will overheat. This can be determined by the temperature gauge on the instrument panel, while the radiator remains cold. However, a faulty thermostat may also remain open after the coolant has cooled. In this case, the engine will not reach its operating temperature or will reach it very slowly, and the power of the interior heater will be reduced.

Note: If the engine overheats after a short trip, the cause may also be that the radiator is clogged with limescale deposits.

Remove the thermostat.

Slowly heat the thermostat in a container with water. The thermostat should not touch the walls of the vessel. The thermostat should be completely immersed in water. The temperature should be monitored using a thermometer.



At the opening temperature, i.e. about 85°C (for diesel engines - 70°C), the thermostat control plate should begin to open.

When cooling, check whether the thermostat closes completely. If not, replace it.

Install the thermostat.