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Plastic tank + saddle tank: Breather line configuration

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difflock
Posts: 317

Plastic tank + saddle tank: Breather line configuration

Post#1 » Sat Sep 14, 2019 10:54 am

Hey folks!

I have a plastic tank paired with a saddle tank that I got installed a few weeks ago by my mechanic. Right after install, I filled it up all the way and was disappointed to find it leaking diesel onto the pavement.

I initially thought the problem was a bad seal between the saddle tank and the plastic tank, so I pulled everything out to inspect yesterday. Everything looked fine and tight, but it turned out that instead of connecting all the breather lines together like in the manual (image below), my mechanic attached hoses to each fitting individually and routed them to a high point near the body. This makes sense in theory, as it would let the air escape, but I am guessing as the tank fills up and air rushes out the high cavities in the plastic tank, some fuel ends up squirting out the end of these exposed breather lines, causing the leak onto pavement.

My hypothesis is that the right way to prevent this is to join them all and route them to the high point on the filler neck, as the manual suggests. This way any splash-back is contained to inside the system, while still letting air get released.

Screen Shot 2019-09-14 at 2.37.52 PM.png


Since I am connecting to a saddle tank, not the filler neck in the diagram, it turns out I don't have enough breather fittings on my saddle tank to follow the instructions in the manual.

The manual describes attaching the tank to a filler neck that has three fittings (24, 25, 29 in diagram). but my right saddle tank has only one breather fitting, as you can see here.

Screen Shot 2019-09-14 at 2.45.44 PM copy.jpg


How can I achieve a properly working system with the components I have?

More specifically, the questions I'm looking to answer are:
- I don't have a steel T-fitting line (7) that the manual assumes is being used. Instead of sourcing one, I am planning to mate the hoses to a T fitting from the hardware store instead. Any better ideas?
- Since I am looking to connect all breather lines to one fitting on the saddle tank, I am planning on joining hoses marked by (14c, 14b) with a Y and connecting them to the single breather fitting on the saddle tank.
- What fittings should be plugged up in my configuration? The manual mentions 9 and 19. Any others?

This is my first major "under the car" mechanic attempt on the G, so any advice or tips appreciated :)

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cal_w460
Posts: 1908

Re: Plastic tank + saddle tank: Breather line configuration

Post#2 » Sat Sep 14, 2019 11:17 am

You can just run the breather lines a bit differently.

- One pipe from the left to the right of the plastic tank.
- Add a T or Y connection to the right end of that cross pipe. The two free connections then ties up all the left nipples with soe rubber fuel hoses.

I used 1/2” stainless steel pipes with press nipples to replicate that OEM cross pipe. Added a T-connection in the middle and a short pipe to the fuel sender breather.

This is not rocket science. Just make sure nothing rubs against the body or other parts.

I also added a large MAHLE fuel filter to the end of the breather pipe, before it attaches to the filler neck (saddle tank in your case). To prevent dust, mold particles and other stuff to enter the tank.
w460.333 1982 Colorado Beige 300 GD OM617.931

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vadimivanovich
Posts: 7836

Re: Plastic tank + saddle tank: Breather line configuration

Post#3 » Sat Sep 14, 2019 11:38 am

I used hardware store fittings to connect all of the vent lines to the filler neck. Works just fine - but be sure your fuel cap is the vented version (diesel).
"The way you think is the way you live"

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Fernando BR
Posts: 1905

Re: Plastic tank + saddle tank: Breather line configuration

Post#4 » Sat Sep 14, 2019 12:43 pm

I am using only one saddle , 2 are not possible. One breath is direct from saddle .Mercedes says it is not ok to use saddle with plastic tank.I am using for more than 7 years.
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difflock
Posts: 317

Re: Plastic tank + saddle tank: Breather line configuration

Post#5 » Sat Sep 14, 2019 1:23 pm

The Mercedes diagram looks overly complex, no? Is that necessary? I am not even sure what is going on.

My plan is to do something similar to the diagram, but with hardware store fuel hose and fittings. I will put a Y fitting at the area labeled 24 in the diagram so I could merge the two hoses to the one fitting on the tank.

Something like this:
19F41341-6691-4EB5-AD7A-67A7C2930EF4.jpeg

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vadimivanovich
Posts: 7836

Re: Plastic tank + saddle tank: Breather line configuration

Post#6 » Sat Sep 14, 2019 1:50 pm

Seems fine. Again, please verify that your gas cap is the vented version. If not, you can drill a tiny hole and make it vented. Without that you will build a vacuum in the tank until the engine shuts off.
"The way you think is the way you live"

difflock
Posts: 317

Re: Plastic tank + saddle tank: Breather line configuration

Post#7 » Mon Sep 16, 2019 2:09 pm

Got it in, surprisingly wasn’t so bad!

Is it ok for the rear cross member to press against the tank? That’s how it fit in, seems to be a correct tight fit all around. And I am using the rubber strips against the frame.

A87299CA-0028-4ADA-9964-5B8A1748DACF.jpeg

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cal_w460
Posts: 1908

Re: Plastic tank + saddle tank: Breather line configuration

Post#8 » Mon Sep 16, 2019 7:16 pm

I put a piece of rubber inbetween my plastic tank and that cross member.
w460.333 1982 Colorado Beige 300 GD OM617.931

difflock
Posts: 317

Re: Plastic tank + saddle tank: Breather line configuration

Post#9 » Tue Sep 17, 2019 9:01 am

vadimivanovich wrote:Seems fine. Again, please verify that your gas cap is the vented version. If not, you can drill a tiny hole and make it vented. Without that you will build a vacuum in the tank until the engine shuts off.


Thanks for the tip! Is my cap vented?

Seems like tiny holes in the marked area.
D74485B4-253F-4A18-85B6-383DD2F8D316.jpeg

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AlanMcR
Posts: 4283

Re: Plastic tank + saddle tank: Breather line configuration

Post#10 » Tue Sep 17, 2019 9:42 am

Says "Mit Ventilbelüftung" - so "with vent".
...Alan

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