W140 M104 ECT Sensor
 

Can you just replace the ECT and CT sensor as a DIY project?

Do I have to drain the coolant? Can I just unscrew the old one and screw the new one in?

Thanks. I am looking for an easy way out. If draining is required, I will leave it to the pro...

It's an easy DIY job. Just make sure the engine is cold, and replace the seal ring(s). No need to drain anything. Good luck

Henry, to make it a . . .
 

"messless" job, drain the overflow bottle. Use a siphon to remove the fluid, maybe all of it. You can save it and pour it back after the new sensors are installed.

As you remove the two sensors, it will be clean, ie no af/water. That's what I'd do! :)