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.

Coolant Leak
 

Important omission - the car is my 1989 300E!

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.

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