How do I swap the thermostat in a peugeot 405 1.8 GLX 1995?

Where is the leak? Can you actually see it or are you having to top it up alot? If you cant see a leak check for damp carpets or water in the oil. Don't fill the rad beyond the max level as it will only blow it out when it gets hot.
Sorry I answered your question regarding where the thermostat is but this is unlikely to cause a leak, but would cause high temperature if sticking in shut position.

Mark
December 2005

Follow the thick hose from the top of the radiator on the passenger side to the thermostat housing on the cylinder head. From memory I think there are two bolts on the housing cover. When you have fitted it, make sure you get the air out of the system to avoid air locks. There are bleed screws on some of the pipes in the cooling system and also on the top corner of the radiator on passenger side.

Mark
December 2005