Cooling system bleed

QI hope that I have nearly reached my objective in bringing the servicing of my 2007 Skoda Octavia 1.6 FSI (BLF engine code) up to date and many thanks for your help with this. The next job is to change the coolant. In the old days this would be a simple operation, but I have been told that when refilling the thermostat must be opened electronically by some sort of an external device to ensure that the system is free of air. Surely the temperature would open the device and leaving the filler cap open and watching for the bubbles, etc, would complete the operation? I wonder if this is another manufacturer’s anti-diy contrivance? WHA Burgess

AThe thermostat fitted to your Skoda is a standard temperature-operated unit and has no electronic components. As you correctly say, the thermostat will operate and open as the temperature in the cooling system rises. Whoever informed you of the need to open the thermostat electronically may have been getting confused with the bleeding instructions for vehicles with auxiliary heaters. On these vehicles the coolant shut-off valve needs to be activated via the VAG diagnosis system VAS 5051B.

The official VAG instructions for bleeding out the cooling system without the auxiliary heater fitted are as follows: first, mix the coolant additive and water in the correct ratio and fill up the cooling system to the ‘Max’ mark on the expansion reservoir. Fit the reservoir cap and seal the system, then turn off the air-conditioning and heating system. Start the engine and maintain the engine speed at 2000rpm for around three minutes, then allow the engine to run until the radiator fan starts. Check the coolant level and top up if required, taking care when releasing the coolant reservoir cap to avoid scalding. I would also check the cooling system pipes as the engine warms up, to ensure the coolant is flowing through the system.