Motor temperature sender 3 Pin R1/2-14G

Front diameter 14mm; length 11mm
Thread outer diameter 20.8 conical
Air is trapped in the coolant system.

If coolant is added too quickly when refilling the cooling system, air can become trapped in the engine block/head. This causes the water pump to run dry and it cannot remove the trapped air from the system itself.
To top up the cooling system properly:
1. loosen the coolant temperature sending unit, part number 2852157, (see PAL / Support Pro 0.32.6) at the rear from the head enough to allow air to escape from the block / head. Do this with the radiator cap removed to allow the heat exchanger level to fill the engine. Sometimes pumping (pushing) on the hoses with your hand will help the coolant move the air. 2.

Fill up slowly with coolant until coolant flow is detected at the temperature sender from the head. Tighten the sender again. This allows coolant to reach the water in the pump. Confirm this by pumping the hose by hand until resistance is felt from the coolant, in the hose. 3.
Start the engine and watch through the radiator cap to ensure that coolant is seen flowing through the heat exchanger when the thermostat opens. Fill the heat exchanger with coolant and close the system immediately to allow pressurisation. Do not continue to run the engine if no coolant flow is detected as this could indicate a faulty thermostatic valve and cause an overheating condition.