Heres a 'how to' on replacing a thermostat on a Clio Mk 2 Phase 1(1998 onwards) 1.2 Petrol 8 valve(may also be relevant to other petrol engines in the Meganes and Clios).
The one I changed today was leaking,but this could also be of help if the thermostat is faulty(cool running if 'stat stuck open,over heating if 'stat stuck closed).The thermostat is only available as a complete housing,and the one I used was an aftermarket part(First Line part no. FTS 423.89,Genuine Part no.7700 110 716 B) and was around £15 plus the dreaded.The unit is situated on the right hand side of the cylinder head(when viewed from the front),and is directly above the
sensor.The sensor is tempramental at the best of times,but coolant leaking from the housing(as I had today) and getting into it and the wiring connection can only make matters worse!.
First off,make sure the engine is cold.Remove the air intake hose by pulling one end off of the air filter housing and twisting the other end out of it's bracket.You then need to remove a bracket which supports the intake hose and a vaccuum valve on the front of the head,this is held on with one 13mm headed bolt.You should then be able to see the thermostat housing.There are two hoses connected to it(one from the radiator and one from the heater system),these will obviously be filled with coolant,so either be ready with a bucket under the car or do it somewhere where you don't mind getting coolant on the floor.Draining anti-freeze into a drain is illegal,so don't do it blah blah blah!.....
The hoses are held on with spring clips.These can either be removed with a pair of pliers(be carefull,because if the clip slips out of the pliers and hits your fingers it bl##dy hurts!),or by using the special tool for them(a cable operated compressor which grips and squeezes the clip and doesn't allow it to spring open).You can then remove the hoses.Next,undo the three 10mm headed bolts,and the unit will come off.Clean the face on the head with some Emery cloth(or similar),and refitting is the reversal of the above procedure(in the best Haynes book of lies fashion...).
You'll need to top up the coolant and bleed the system.Undo the bleed cap on the thermostat housing,put the car heater temperature setting onto hot,and start the engine.Keep the coolant topped up(with 50/50 anti-freeze/water mix),wait for it to come out of the bleed cap and replace it.Run engine at fast idle(around 2500rpm),and make sure the heater gets hot.Replace the header tank pressure cap and wait for the radiator cooling fans to cut in.Turn the engine off and allow to cool,top up coolant and check for leaks,and then Roberts your mothers brother,job done.
Heres some 'interesting photos'....
The thermostat housing.....(The bleed valve is the part that looks like a tyre valve cap.You remove this to bleed air from the cooling system).
The thermostat is the gold part in the middle of the housing...
And finally,this is the evidence that the housing had been leaking.The white crusty stuff is the residue left from the leaking coolant.It was infact the rubber seal that was leaking,but this is not available seperately.You could reseal the seal(if you know what I mean...) with gasket sealer or simialr and re-use it,but it's really not worth faffing about for something that only costs £15 or so,and theres always a chance it will leak again.