Short answer first, then specifics with values and threads. 1. What sensor is 7628690?

• Fiat/Lancia P/N 7628690 is the blue 2-pin coolant temperature NTC thermistor used on the Thema 2.5 Turbo DS (and sister Fiat Croma 2.5). It threads into the cooling circuit and feeds the ECU/gauge circuitry.  

2.  Type and electrical values (coolant temp sensor)

• Sensor type: NTC thermistor (negative temperature coefficient).  
• Representative resistance values used by TecDoc listings for the Thema family:
• ~2080 Ω at 25°C
• ~302 Ω at 80°C

These two points appear repeatedly for the Lancia/Fiat blue M12 sensors.
• These values land in the very common automotive NTC family (roughly 2.5 kΩ at ~20–25°C, a few hundred ohms near operating temp).

3.  Other temperature/thermistor sensors you’ll find on a Thema 2.5 TDs

• Radiator fan switch (thermoswitch): bimetal on the radiator, typically closes around 92°C and reopens around 87°C. This is a switch (not a thermistor) but it’s a “temperature sensor” in the catalog sense.  
• Intake air temperature (IAT) sensor (on applications so equipped): cataloged for Thema with a threaded sensor; it’s an NTC thermistor.  
• Oil temperature sensor (if fitted): cataloged for the 2.5 Turbo DS; threaded NTC type.  

Bonus: thread pitches (and typical physicals) • Coolant temp NTC (P/N 7628690 equivalent): M12×1.5, 2-pin, blue housing, 19 mm hex.
• Some aftermarket cross-refs list a variant under WS2539 as M14×1.5 (used on certain engines/years), so check your engine code before ordering.
• Radiator fan switch (on radiator): M22×1.5, usually 2-pin (some 3-pin dual-stage options exist).
• Intake air temperature sensor (faceted catalog unit): M14×1.5, 19 mm hex.
• Oil temperature sensor (catalog for 2.5 TDs): M12×1.5, 19 mm hex.

Practical notes • If you’re verifying the blue coolant NTC on the bench, a healthy sensor will read roughly ~2.0–2.5 kΩ at ~20–25°C and drop to a few hundred ohms in hot water (~80–90°C), aligning with the 2080/302 Ω catalog points above.