Symptoms - Random warning service light on dash, sometimes every 5 mins.
Engine code - P0599(12) controlled thermostat control
Citroen guidance - went for new thermostat as a first step
Purchased: METZGER 4006417 Engine thermostat - https://www.autodoc.co.uk/metzger/17013 ... thermostat - £83 with delivery
On arrival - all looks okay, I did notice that the thermostat could be removed although its sold as 1 entire unit.
Following the workshop manual you can replace it, some of the mounting screws can be a pain to reach but overall it's not too bad.
Drain coolant, remove battery and mount, remove the coolant hoses and electrical connectors (yellow one snapped on me when removed)
After fitting the new part, I noticed the coolant tube that was fixed to the rear was loose compared to the original - see below (grey to the right of bolt 1):
The problem I had is that I damaged the yellow electrical connector when removing - typical moment when working on the car
Solution - I carefully removed the thermostat and the temp probe from the new housing and replaced it with the old housing. The green probe is easy with a retaining clip, but with the thermostat I used a small flat head screwdriver to gradually get it out. Its tight, and easy to deform the plastic, but with the screwdriver and some water pump pliers you can get it out.
I would advise not to put any pressure on the plastic which houses the yellow connector as it could break.
Also use the new sealing gasket.
Here are the parts removed:
I'm not sure if the other thermostats offered would be the correct dimensions, but I would personally advise against purchasing METZGER 4006417 for part number 98 121 314 80 even though its listed as compatible.