Hello,
I just updated #20 (to have it all together) as I found in the meanwhile a 100% fitting expansion tank for 2.5T and early 2.2 TDCI.
Many thanks to digdog for taking pictures for me of his car! 
I also found a fitting version for 2.2 TDCI from aftermarket with really good quality: NRF 454092 Quality "looks and feels" like original equipment.
So overall for every Mondeo MK4 there's an expansion tank available with Sensor:
| Engine type | Ford no. without sensor | Volvo no. with sensor | Aftermarket with sensor | Picture |
1.6 TDCI, 2.0 TDCI, 2.2 TDCI (10.04.2008 - 22.12.2014) | 1460978, 6G91-8K218-FA | no 100% suitable found | NRF 454092 |  |
2.5T, 2.2 TDCI (03.03.2008 -10.04.2008) | 1453048, 6G91-8K218-DC | 31200322 | tbd. |  |
1.8 TDCI 1.6, 1.6 EB, 2.0, 2.0EB (203PS/239PS), 2.3 | 1449986, 6G91-8K218-AD | 31439508 | tbd. |  |
As the availability of a risk free sensor system (as used in series in other cars) is clarified, next step is the harness connector.
If my cross check is correct, it's a "MOLEX MX64".
Potential part numbers with code A:
without CPA: 31402-2100

with CPA: 31402-2110
CPA = Connector Position Assurance: the red peace to check that the connector is locked correctly and also blocking the locking mechanism

Fitting terminals: GET 0.64
Tyco part number: 1393366-1 for 0,5mm² - 0,75mm², tin plated
Tyco part number: 1393366-2 for 0,5mm² - 0,75mm², silver plated (works normally also on tin plated pins as counter part)
As there are so many part numbers, I have to check here more.
Next topic would be: "How to indicate missing coolant"?
Checking the sensor I found:
Coolant level OK => Circuit is closed
Coolant level too low => Circuit is opened
So if everything is fine, the circuit is closed.
So it can not be a signal to put the above mentioned pin 13 on ground. Or it is inverted somehow.
Is there maybe an expert here, who nows more how this is done?
Without a real chance that this pin 13 could work, I hesitate to check it with my BCM, not to kill it.
Looking forward for useful hints and advices... 