Coolant Leak

I replaced a coolant sensor recently (the one that screws into the block aft of the coolant bleed screw), because the previous one was leaking coolant.

Unfortunately, the leak persists. Questions-

1-What is the sensor for?

2- Does this sensor require a sealing ring or washer to stop the leak?

3-Will applying a high temperature-resistant sealant to the threads impair the functioning of the sensor?

4-In short, what is the best way to stop the leak?

The leak is slow, but is enough to annoy. Thanks in advance for your advice.

Important omission - the car is my 1989 300E!

[MikeTangas]

Not to sure on such a new car, but I think that is the temp sensor for the aux fan. Yes it should have had a new copper washerwith it, and yes you need that washer. You shouldn't need any high temp pipe dope, but a little teflon tape won't hurt.

To repair, remove the sensor, install copper washer on sensor with 1 or 2 wraps of teflon tape to threads, reinstall sensor, attach lead to the post and admire your handywork.

[vinamg]

Just make sure that the copper or aluminum washer is in place. If it is, get a new one. Also, be careful not to overtighten. I wouldn't use any teflon or sealant. Some of the sensors require a ground.

Vinamg