How to drain and fill DEF
Thread Starter
Newbie
Joined: Feb 2026
Posts: 3
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From: Aurora, CO
ML350 Bluetec
How to drain and fill DEF
Hi all,
This is my first post so please forgive me if it’s in the wrong place.
I am a new owner of a 2012 ML350 Bluetec with approx 134k miles. The SUV has had many if not all of the emissions recalls done by the previous owner and seems to run very well. However I suspect that there could be an issue with the DEF caused by very few miles being driven recently.
I would like to drain and refill the DEF tank (according to the ECU display it is full) with fresh fluid but it seems it might not be as easy as it sounds. I tried to insert a 1/4 OD piece of flexible tubing into the tank but it goes in about 13 inches and stops without getting wet so I think that option is not going to work.
One of the local Mercedes service departments has offered to vacuum out all the old fluid at a shop rate of $260 per hour plus tax. They won’t commit to the total possible cost for the procedure. I called a local independent service shop that said to bring it in and they would do it for $240 per hour but they don’t have the necessary equipment to vacuum the fluid out. So they would have to remove the tank from the vehicle to drain it.
I’m pretty handy with tools so I think I could get the tank removed and drained if I could find a write up or YouTube video of the procedure but I haven’t found it yet.
Can anybody provide some guidance?
thank you
Tom
This is my first post so please forgive me if it’s in the wrong place.
I am a new owner of a 2012 ML350 Bluetec with approx 134k miles. The SUV has had many if not all of the emissions recalls done by the previous owner and seems to run very well. However I suspect that there could be an issue with the DEF caused by very few miles being driven recently.
I would like to drain and refill the DEF tank (according to the ECU display it is full) with fresh fluid but it seems it might not be as easy as it sounds. I tried to insert a 1/4 OD piece of flexible tubing into the tank but it goes in about 13 inches and stops without getting wet so I think that option is not going to work.
One of the local Mercedes service departments has offered to vacuum out all the old fluid at a shop rate of $260 per hour plus tax. They won’t commit to the total possible cost for the procedure. I called a local independent service shop that said to bring it in and they would do it for $240 per hour but they don’t have the necessary equipment to vacuum the fluid out. So they would have to remove the tank from the vehicle to drain it.
I’m pretty handy with tools so I think I could get the tank removed and drained if I could find a write up or YouTube video of the procedure but I haven’t found it yet.
Can anybody provide some guidance?
thank you
Tom
