Glow Plugs Part Number
 

For a 2008 E320 Bluetec I saw one post saying that the glow plugs voltage is not 12V. I also read an article that ML 320 glow plugs are 4.4V or 7V
Can someone clarify it and, if possible tell me the OEM glow plug part number for a E320 Bluetec?
Is it suggested to change all 6 or change only the bad ones?
Any advice about some special tip or care when changing these plugs?
Thanks.

Not sure about OM642 but on OM648 it is BERU # GE 116; 5 volts

It is up to you where you buy from but you can look in the Pelican Parts Catalog and see the Glow Plugs and part numbers you need. Use only Bosch or Beru Glow Plugs.
If you get the correct plugs the voltage should not matter. Unless of course you think you are getting too much voltage and that is killing your plugs.

I have not read stuff on the newer models as you have to know if they Glow Plugs get stuck in them as sometimes happens on the other diesel models that have aluminum cylinder heads.

So there could be a tough choice. Change all of them and risk snapping of one or more what were working glow plugs in the Cylinder head or limit the risk of so many snapping off and only replace the bag Glow Plugs.

Once a Glow Plug is out you should ream out the Carbon with a reamer or some other alternative method.

When the glow plugs are installed use some never-seeze type compound n the threads.

US 2008 bluetec uses beru gp controller so I presume it uses beru gp ge105 which is 4.4v. the best is to take one out and check. Don't buy Bosch unless you are very sure as it may be European spec.

The stuck glow plugs issue seems to be only on the 606 motors, I've almost never heard of it happening on any of the others, and zero about the current engines like the 648/642/651....

Yes, this weekend I took one plug out of the engine and found all this numbers engraved on it:

CZ 302 7V K72 MK
A 001 159 57 01 NGK

It is a 8 mm thread and was very easy to be removed.
I also replaced the glow plug controller and the glow plug warning sign on o the dash board is gone.

When I had the glow plugs replaced back in 2015 (I used the dealer, paid $$, was traveling for weeks on end at the time) on our ML320 they used
642 900 57 01 controller
001 159 66 01 glow plugs

The only problem that I had with the controller is that the original from MB on my car is bigger size than the new one that I bought and the harness are made just long enough to reach the controller.
At the time to install the new one, the round connector is not long enough to reach the new controller. In order to get this installed I need not to use the long bolt + nut in front of the controller.
I try to re-route the cable but even doing this the connector will not reach the controller. So, I did not use the controller front bolt+nut.
I don't like that.