Renault Clio dCi thermostat replacement

My 2003 1.5 dCi (65) was running slightly cool and the temperature needle would drop by one or two notches with the engine under low load conditions, such as motorway driving. It never used to do this and the needle would always stay in the centre under all driving conditions. These symptoms are indicative of a thermostat that is failing in the open position, so I changed it.