There's two temperature sensors on the OM617 block, drivers side. One for the in-dash gauge and one for the preglow relay.

I want to replace one of these with a generic aftermarket sensor, so I need to know the correct thread size for the part.
Available at the store are M14, M16 and M18 sized.
Which goes into the OM617?

Thanks a lot!

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Tomas, Sweden
1966 Mercedes Benz 230S with OM617.912, automatic. Disk brakes from W108
1983 Mercedes Benz 300TD grey, OM617.912 and 5-speed manual
1983 Mercedes Benz 300TD blue 7-seater, OM617.912 and 5-speed manual