I don't know the specifics of the OM617 but on OM603 the 3 prong temp switch has a M14 x 1.5mm thread. You'll have to check if the your engine is the same. There are 2 BMW temperature switches with this same thread. BMW mounts them directly into the radiator hence the lower temp ranges.

ÜRO PARTS Part # 61318361787 = 80/88c

ÜRO PARTS Part # 61311378073 = 91/99c

Rock auto has them for $11 but they charge for shipping. It only makes sense to buy from them if ur getting other stuff shipped from same location. You will need to grab the BMW electric plug from the JY and splice it into your wiring harness.
http://doozaadoozaa.webs.com/immage/temp_sensor_pole.jpg
http://doozaadoozaa.webs.com/immage/temp_sensor_plug-circuit.jpg

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CENSORED due to not family friendly words