The wire contact connected to the Coolant Temperature Sensor of my Mercedes OM636 (Boat engine same as Mercedes 170D, 180D) was corroded and got accidentally snapped off. Can I just solder this back on and and therefore save the £42 for a new Coolant Temperature Sensor?
I would think you should be able to if there is a terminal for the wire to attach to. If the terminal has broke off at the base of the sensor, then it probably won't work. I would use a soldering iron, versus open flame type of iron to ensure the heat is more localized. If you are worried about the sensor not working due to the heat, I don't think I would worry about it too much. Think of it this way, if it doesn't work after you reconnect it, it needed replaced anyway. It will cost you nothing but a little bit of time and solder to try it. If it works, you're golden. If it doesn't, you aren't out much for trying.