check there are no blockages in the flow from the engine rad. upper hose should be hotter than lower. significant difference would suggest a blockage. Often caused by not flushing the coolant often enough. I'm sur it will be the thermostat. It may be opening the flow to often, sort that with engine recommendations as it affects fuel economy and we all need to do our bit for the environment.
Wish peugoet thought of that when they designed this car!
Big D
February 2009