How to replace the coolant thermostat on a Volkswagen Golf IV

Let’s see how to replace the thermostat on a Volkswagen Golf IV (also known as Bora): The work should be done with the engine cold, and it is advisable to disconnect the negative terminal of the battery; place a container under the radiator, open the cap of the expansion tank, and drain the fluid. The thermostat is located at the bottom, on the right side of the engine and is covered by other components. You will need to remove the lower timing cover, move the secondary air pump, which is secured with a few 10mm bolts. It is also helpful to loosen the engine mount and then lift it with a jack: this will give you more space. Disconnect the cooling hose entering the thermostat and drain the residual fluid; remove the thermostat housing, and then use a flat screwdriver to remove it. Clean the seat thoroughly, removing any traces of the old gasket. Insert the new thermostat - which can be found on Amazon with the code B0DRYL5K2P for £14.99, with free one-day delivery for Prime customers - with the new gasket into its housing. Reconnect the cooling hose and reassemble all components that were removed or moved from their place. Close the radiator drain cap and pour in the coolant according to the manufacturer's specifications, into the expansion tank up to the "max" mark. Now, you need to bleed the air by leaving the expansion tank cap open and starting the engine at idle. Set the fan to maximum temperature and minimum speed; the fluid level will drop, and you will need to add fluid to maintain it at the max level. When the engine reaches operating temperature and the radiator fan activates, the air has been bled.