Hi Everyone, 2005 E320 CDI with 3.2 L inline 6.
Temperature on dash readout has been quite low (50 - 70 degrees) within last few weeks as outside temp has gone below 0 degrees. Also noticed that fuel economy hasn't been its usual self. From this forum, I learned that its time for a new thermostat.
Got a new thermostat and jug of coolant from the dealer last week and installed it today since it was and acceptable temperature outside here in the Great White North (Ontario, Canada)
From this thread, I learned that the new thermostat has one hole that screws the clip to hold the fuel lines that isn't tapped. No big deal as I have some M6 x 1 taps and tapped the hole no problem. I wonder if the Benz designers purposely designs things to make life more difficult for the DIY people, or is it a simple manufacture issue where an engineering change never made it into the part. I came from the automotive manufacturing world and believe me this wouldn't be the first time something like this happened.
Install was not difficult, but I really wanted to take my time since it is the first time I have attempted this. Got all bolts out with a 3/8 drive with swivel and a female torx, but a quarter drive might have been a bit easier, (although my female torx bit needed a 3/8 drive).
Once the three bolts holding the thermostat were almost out, I used a magnet to hang onto the bolts, just in case a bolt decided to drop down to who knows where or even down the oil filter opening which I removed to get better access for bolt removal. Did stuff a rag into opening just in case of an errant bolt or even some coolant loss into the oil.
Lost maybe 3/4 liter when I pulled the large hose off, but a well placed rag caught a good portion the coolant. I could have minimized coolant loss had I heeded the advice to drain the coolant from the expansion tank first.
Topped off with 50/50 coolant and distilled water.
Sure enough within a few kms of driving, the dash temperature readout was right around 90, just where it should be.
Cold beer time.

Sorry to ramble on, but I do have one question for any of you Benz gurus.

Found this on YouTube, Mercedes W211 How to use hidden AC menu.
On the AC panel, Hold the "OFF" and "REST" button simultaneously, looks to be around 5 seconds, which will access a menu with a number of sensor functions,
The functions are:
1) in car temp
2) temp outside
3) heater core temp, left
4) heater core temp, right
5) evaporator core temp
6) engine coolant temp
7) refrigerant temp
9) not used
10) blower control voltage in range 0.8 - 6V (max)
11) air pollution sensor
12) sun sensor
20) control current of aux fan
21) engine RPM (x100)
22) vehicle speed, km/hr
23) terminal 58d battery charge, percent
24) battery voltage
40) software status register
41) hardware status register

I really wanted to find out my coolant temperature before I undertook changing out the thermostat, just to make sure that I was addressing the real issue. It all worked out of course, it actually was my thermostat.

Accessing this menu on my car did not work. The video shows press and hold "OFF" and "REST" to access and same to exit. I tried it with the car running.

My 05 CDI has a "O" button where the video shows "OFF" button. Also tried the AC OFF (far right button on my car, and the "REST" button, but this did not work either.

Anyone have an insight so I can access this function. Looks like this vid was made in Germany, so maybe Euro cars and NA cars are different?

Thanks for any responses.

As a newbie Benz owner, I wish I had got one sooner, by far the best car I have ever driven.