How do you bleed air from the cooling system of a Peugeot 306 HDI?

To bleed air from the cooling system of a Peugeot 306 HDI, first ensure the engine is cool. Remove the expansion tank cap and start the engine, allowing it to reach operating temperature. Turn the heater to maximum and keep an eye on the coolant level; as the thermostat opens, air bubbles should escape. If necessary, top up the coolant and repeat the process until no more air bubbles are visible. Finally, replace the expansion tank cap securely.