With reference to changing the sender unit for the temperature gauge, I carried out this job on my 1.6 Zetec engine three weeks or so ago. I undid the top hose, and moved it to one side, then I undid the smaller hose underneath, and moved that to one side, then put a ring spanner on the sensor and unscrewed it. It was as easy as pie.
When fitting the new unit, I wound a few turns of white plumber's tape around the thread, and screwed it back in and tightened it up firmly with a ring spanner. I topped up with antifreeze/summer coolant and that was it. It was all up and done in less than twenty minutes. I never found any need to remove the thermostat housing, - and never even considered I would need to do so. Many thanks, Cooderkey.
PS I bought the unit from an eBay seller called ' transitpartsuk '. This was a very friendly and efficent business seller. They shipped quick, and were not expensive, and the staff were brilliant and seemed to know what they were doing.