Hi Craig i know this is very late but it may help someone like me in the future. i searched google for skoda thermostat replacement and this was the only briskoda thread that came up. on selection i realised no one had managed to answer your question hence i could not tell where or how to replace my thermostat.
Therefore, i was forced to go in blind.
The thermostat on an octavia 1.9tdi 2005 is located just the the rear right hand side of the alternator. it is uncharacteristically fed from the lower radiator hose up to the side of the engine block. the thermostat housing is held into the block by two 10mm bolts. At first glance it looks as if you will need to remove the alternator and other pipes etc. This is not the case.
The removal of the two bolts can be carried out using a half inch drive ratchet with an extention bar attached to a universal joint (nuckle) and a 10mm socket. once the bolts have been untightend to their fullest degree, i found they were easily removed and replaced using a telescopic magnet, you could use your fingers if you have piano hands, mine are like a bunch of bananas (huge).
Pull off the housing still attached to the lower hose and push to one side.
Remove the old thermostat and rubber seal.
Replace using a new thermostat and rubber seal, the replacement seal usually fits onto the thermostat.
Once in place the housing can be placed back into position and then the bolts put back into the holes.
Care should be taken when tightening the bolts, do not use the ratchet for the first few threads to ensure they are not cross threaded.
Then tighten hand tight and a bit, dont over do it or you will break the plastic housing.
One more tip, if replacing in the winter as usually the case, warm the engine slightly first not too much. but this will make things less brittle when tightening.
Hope this helps someone.
