air in fuel line after changing fuel filter


New member
full an idiot...I was switching the fuel filter on my 2003 3500 and in doing research before i read that you dont need to but fuel in the filter and it will self prime. Well that was incorrect and now i have air in the fuel line. Ive gone and filled the filter up with Diesel and have proceeded to try and crank through the air but to no avail she will not turn over. Ive done quite a bit of searching through posts and not really coming up with much. I dont see how to bleed the system and a local mechanic has told me that he thinks i need to bleed the injectors which doesnt sound fun. Any help would be greatly appreciated. cheers.
Do you see air/bubbles in the clear lines? I did this for the first time recently and after some cursing and such I was successful in priming it. Here's what I did:

loosen bleed screw on the top of the fuel filter

remove fuel line from the low pressure fuel pump (front of the engine - black/white horseshoe clip)

fill fuel filter and lines through a fuel line and funnel that is long enough to be higher than the aforementioned fuel pump. fill until fuel comes out of fuel pump inlet.

reattach line to low pressure fuel pump

reattach input fuel line from fuel tank to fuel filter

curse threateningly

crank away


'02 140 Hi BlueBlk Pass
I presume you are talking about a OM612 2001-2003 T1N, as the OM647's have an electric pump in the tank and this should not be an issue for those models.

Priming is always a good idea to reduce overheating the starter, lowering the voltage on the battery below 11.5 at which point you get the dreaded START ERROR, and possible damage to the low pressure pump.

For years I did the funnel/turkey baster technique (my PDF from 2003 is still posted) But Dr. A has a better method. I don't have pictures of this - so next week [NOW POSTED] I will post a thread on this. But in the meantime, if you have access to a VOSS fitting (I got mine from the old clear line that I replaced). Strip off the black clamps and white spreader. Heat gun off the nylon line. Attach a 6" or so length of fuel line on the fitting. Remove the TOP fitting on the low pressure pump. Check its O-ring, then silicone grease it. Now install the stripped down fitting. Attach a vacuum pump like a Mityvac pump. Pump away. You will be able to see fuel work its way up into the pump. I like to let it sit for a couple of minutes to see if there is an air leak. Now the tricky part. You have to quickly remove the vacuum line fitting and replace the fuel line (that is why the bypass fitting is stripped of the clamp and the fuel line is prepared ahead of time). You will lose a little bit of prime, but not much. Restarting time and wear and tear on the system is considerably reduced.

In the absence of a VOSS fitting, try to find a rubber cone fitting with a right angle that will fit in the pump's exit port to set up the vacuum pump.
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New member
The first few time I changed the filter, I had to go back and re-do connections several times before the air would stop. For 02-03 OM612 engines:

some things I learned:
1. Get a fuel filter without the water sensor/drain fittings. Two less things to leak air.
2. Always have a full tank of fuel before changing filter. Less distance for fuel to flow back in the line.
3. Clamp the fuel line from the tank before removing it from the old filter. Fuel will have less chance to get sucked back to tank.
4. Never use Hasting filters. They are slightly off and will not provide a good seal at the top connections.
5. Don't panic if 20 seconds of cranking doesn't clear the lines of air. Sometimes it takes several tries of 10-15 seconds each, a couple minutes total. Have a jumpstarter or spare battery on hand if needed. I don't like to run a starter more than 10-15 seconds for fear of overheating it, despite what the manual says about cranking for a minute or more to purge.
6. Air is purged automatically by the system. Much cranking may be needed to remove enough for the engine to start if a fumbling filter change was made.

7. Never did this, but installing a cheap electric fuel pump between the tank and filter can remove air from the system without extended cranking. Maybe on a bypass loop so it can be isolated from the regular fuel line once the filter change is successful.


New member
This is my follow up. I used every method mentioned to try and push or pull the fuel through the fuel system to try and get primed again. I gravity feed fuel through the fuel line, pressurized the fuel tank, and mighty vac'd through the fuel pump...the ladder being the most efficient in my opinion and thanks to HKpierce on his help with that method Regardless what i found was air in the system coming from the fuel filter and joining the basic consensus that you need the fuel filter design WITHOUT the water sensor port/ water drain port. After installing that...she fired up and is now fine.
So one question is that im still concerned with not having those features because its my understanding that if water gets in the engine it is devastating. And being that the fuel filter that i replaced had the water sensor design and it had worked fine i feel like i still want to get that fuel filter to ill keep trying...Anyway Thanks to everyone and hope this helps others.
I had the same problem. I replaced the clamps on the fuel lines to no avail. On my rig the problem turned out to be the itty bitty o-ring at the end of the water bleed screw. I think the replacement cost a couple dollars at the Mercede$ dealer. The old o-ring was deformed I think from being overtightened.

Aqua Puttana

Poly - Thread Finder
... The old o-ring was deformed I think from being overtightened.

Tighter is not always better when it comes to O-ring seals. Correct installation is.

Posts here do show that a filter with no WIF sensor makes things easier. Funny that so many Sprinters all over the world are operating with the OEM WIF filter design intact.

WIF isn't reported as being very common. If it happens and you have no warning there can be serious consequences. I choose not to roll the dice, but I don't have a OM612 engine.

Water in Fuel Light WIF warning is on.



Former Nelson BC Sprinter
I have the Bosch fuel filter without WIF sensor hole or water bleed screw if anyone needs one mailed out it's $47 with postage from Canada


New member
Eliminate air in the T1N fuel caused by the MB fuel filter once and for all. The fuel filter assy pictured can be purchase on ebay.
Remove the T on the MB filter from the hoses and spice the 2 hoses together with a 5/16 brass hose barb. Using a 3/8 hose barb connect a new length of 3/8 hose from the fuel tank input that was connected to the input of the MB filter up to the new filter input. Using a new 3/8 hose length connect the output of the new filter to the plastic connector that was on the top of the old MB filter. The 3/8 hose will fit over the O rings on the plastic connector as pictured. Using 14-16mm fuel injector clamps install a clamp at each of the hose connections. I used a strap from Home Depot and mounted the filter to the brake booster. Its not the nicest of installations but my 2003 has 350K miles on it and I don't take it far from home as I never know what will fail next.



2004 140” SHC T1N 2500
Well done! :thumbup:
Be aware that you’ve removed the fuel preheat mechanism, so might wish to avoid driving into freezing temperatures. (but heck, I’D like to avoid that too!)


UK Spec 2002 LWB 311 CDI
Been working on this exact problem today as i'm still tackling the rough idle problem on my UK spec 311 CDI. Having plugged the end of the hose connecting a recent fuel tap i put in the tank i left the van idling for ten minutes hoping the engine note would change, suffice to say it made no difference. So (as i seem to do each Sunday) i got the tools out and started poking around, this time around the fuel filter as having had that lot off as part of a service and then again when removing the tank and lines i thought it a good place to start.

First mistake was to undo the bleed screw slightly to see what would happen, nothing but hissing then the engine died, no bother, popped the pre-heating valve off & syringed a load of fuel back into the filter to top it off, then reconnected then popped off the inlet (tank connection) and sucked the diesel back up to the filter and quickly refitted the pipe. I turned the engine over for about 30 secs with nothing happening so i stopped - mild panic setting in.

Second mistake was whilst checking the filters connectors for leaks i could hear hissing coming from the fuel line connector, the one that's locked by the white 'c' shaped fitting. In fact by now with my ear next to it its making the same noise a balloon makes when you let the air out by hand - sort of high pitch squeaking/bubbling noise. So on deciding to investigate this further i manage to snap one of the tabs off the connector that the white fitting locks - great!

I decided to refit everything and leave the filter alone, & feeling utterly dejected I went to turn the engine over again expecting nothing and to my surprise it spluttered back into life - all good.................. i think.

However on closer inspection of the filter its leaking not only on the fuel line connector but also around the WIF sensor judging by the staining on the bottom of the cannister. I'm hoping the purchase of a new fuel line that connects the LP pump to the filter and a new filter with no WIF sensor may just solve my problems. Having watched said fuel line there's an almost constant stream of very fine bubbles in the line so i'm hoping this is the culprit as many of you pointed out to me.

Also i'm thinking of fitting either a hand primer bulb on the inlet just before the filter, (i've gone off the taste of diesel having done this a few times) of maybe a check valve in the same place, does this sound like a good idea? If the engine doesn't quieten down after that i'm gonna go the re-design route like bubbasprinters done.

At the 20sec mark below i put my phones mic directly next to the fuel line connector fitting and you can hear the squeaky / bubbling noise

And this one you can noticably see bubbles in the fuel line.

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I did a write up on how to convert to the 04-06 filter housing that gets rid of potential air leak spots but maintains the stock filter placement and configuration.


Former Nelson BC Sprinter


UK Spec 2002 LWB 311 CDI
Just a quick update: i fitted my new Bosch fuel filter with no WIF sensor on bottom, bleed screw on top or WIF drain on side so just the pipe connections on the top and a new fuel line that connects the filter to the LP pump and whilst not totally knocking out all the noise at idle has certainly reduced it significantly.

Bosch filter i bought:

Fuel Line:

A couple of pictures here:
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