leave it unless its bugging you or your selling.
Ours has been doing this now for 2 years.
Its very inconsistent but we just leave it.
Yes it is.
I cannot guarantee without seeing its the same fault as ours... but it sounds the same.
Ours sometimes just didn't work at all.
Then after a couple of days worked fine.
Its very inconsistent.
But one thing about a Mondeo.. it keeps prodding along ;)
If its bugging you take it to a garage - if not leave well alone and see what happens.
Mines been doing it for 2 years nearly now. The aircon is on the verge, the tempretaure gauge is hit and miss and the rubbers for the back box need changing every 6 months... but the car keeps going. (Its now done 173,000 miles).
Its not a car - its a tool.
Its a common ocurrence on the mk3 diesels -
The temprature sensor is on metal of the head (its behind the waterpump/ power steering pulley) - this means it reads the actual head temprature, not the water temprature - the thermostat controls the water by opening an closing, diverting the coolant from the radiator, as it goes (slowly) through its close/open/close cycle, the temprature tends to go up and down
The head cools/ heats at a different rate from the coolant, and as the thermostat controls the coolant, there can be a "mismatch"
Also, the engine does not produce a lot of heat in normal use, and the heater tends to take a lot iof heat out of the system, if it takes more heat out than the engine produces, it will not maintain its temp - there is an electrical heater (3 element) built into the system before the heater, im not sure when this comes on, for how long (mabee just for warm up) - in artic countries the MK3 Mondeo has a diesel burner/ heater instead of the electric on we get
The temp sender on the head is useful as if the water runs dry the exessive heat will be read by the sender, and the ECU backs off the fuelling (if the sensor was in the water if it ran dry it would not read it) + if the car has been sitting cooling for a while it reads the head temp and can adjust the fuelling accurately
The engine is said to be "overcooled" and it is a common problem with mk3 Mondeo diesels
If its really bad (running cool) and its not the electric heater elements it could be the second thermostat (small oil cooler thermostat on the waterpump housing)