How to Install the Thermostat on a Seat Toledo and Leon

Let’s see how to replace the thermostat on the Seat Toledo (and also the Seat Leon). Allow the engine to cool down completely; the thermostat is located at the rear of the engine, near the cylinder head, connected to the coolant hoses. For safety, disconnect the negative terminal of the battery, then place a container under the work area and partially drain the coolant.

Remove the upper hose (the one going to the radiator/exchanger), unscrew the 2 or 3 screws that secure the thermostat housing to the engine block, and carefully extract it. Clean the contact surfaces on the engine block thoroughly. You can find the new thermostat on Amazon with code B00ELMB8ZE for £11.88, with free delivery for Prime customers.

For reassembly, there is a critical step, as the thermostat must be seated freely within a blind hole, making it difficult to keep it in position while placing the housing. Position the O-ring in its groove, insert the new thermostat, use a long plastic tie to hold it in place, thread the end of the tie upwards and make a temporary knot, securing the end of the tie with tape so that the thermostat stays pulled upwards and does not fall in when you position the housing.

You can remove the tie once you have inserted the screws, then fill the expansion tank with coolant, after which you will need to bleed the system of air and reconnect the battery.