Fuel expansion tank recovery system question

[Shortsguy1]

Hello-
I have an early w115, 220d, but I think its fuel expansion system is similar to some w108 cars. I removed the trunk cardboard (a while ago) that supported the small plastic expansion tank (or breather system, maybe) with three lines to it, and now I don't know which way the small plastic tank is supposed to be oriented. This is behind the spare tire and normally hangs from the trunk cardboard with a clip (if I recall correctly).



Please see the attached image or this ebay ad for images of the part I am asking about:
https://www.ebay.ie/itm/MERCEDES-PAGODA-W108-250-280SE-W111-W113-FUEL-TANK-BREATHER-1084710081-/282990658527?hash=item41e38ec3df


My system is leaking fuel out the breather hole behind the bumper, so I know I have it oriented wrong. Could someone let me know which way around this thing is supposed to be mounted in the car? Thanks.

[gmog220d]

Does this image from the FSM help?

[gmog220d]

I took a look at my car. The post on top of the compensation vessel goes into a steel clip that's on the card. Have you still got that clip on your removed card?

[Shortsguy1]

Thank you. Yes, that is very helpful. But also confusing. My cardboard basically disintegrated due to a trunk leak. So that is why I have this problem. I have taped the small tank to the car in the orientation shown, so now I don't know why I have fuel leakage. The atmospheric vent pipe to the plastic tank must extend up higher inside the tank, otherwise it would not work. I wonder if I have a blocked nose or a problem inside the plastic tank. Thanks again gmog. I have more to figure out, but those pages help a lot.

[meltedpanda]

those line do deteriorate after time, on my W110 I replaced the all from start to finish , and all was good, not a tough task but tedious. You can find rubber metric hose at most auto stores

[gmog220d]

Hmmm - I too would be thinking about a clogged vent line between the fuel tank and compensation vessel. If one of the two is clogged perhaps fuel could pass through the open one to the vessel and fill it to the point it would overflow into the vent line to the outside, since it can't drain out the clogged line from the vessel back to the tank.

So why two vent lines to the tank? It would be nice to know the routing of the tank vent lines inside the fuel tank. Do they extend to opposite sides of the tank, so when fuel sloshes to one side and into the vent line on that side the other side is clear and able to vent/drain?

Are you experiencing this only when the tank is full, or all the time?

[meltedpanda]

those are vent lines, no fuel should be in them , something is amiss, I have owned MB's for years and years, never had fuel in those lines

[Shortsguy1]

My problem is only when the tank is quite full. I though it only happened right after I had filled up. But I have driven the car about 30 miles since filling up, and it is still happening. Our road has a lot of "crown" and is slightly uphill, so when the car is parked, the right rear of the car (where the compensation tank is located) is definitely the lowest point.

I will double check that the lines are aren't obviously clogged/kinked and make sure that I taped the compensation tank as high as possible on the trunk interior.

melted panda-
The FSM excerpt provided by gmog suggest that it is okay if fuel goes up in those lines to the compensation tank. Thanks for sharing your first hand knowledge as well.

As I learn more, I will write a followup. Thanks for all the help. I really appreciate it.

[meltedpanda]

that seems odd although that it what it says, How would fuel flow up to that level is beyond me, fluid dynamics would say otherwise . i guess vent pressure could force it up?
In any respect I have had a W114 W115 , W110 and never saw fuel in the container .

Curious to know what you find

[gmog220d]

Originally Posted by meltedpanda

that seems odd although that it what it says, How would fuel flow up to that level is beyond me, fluid dynamics would say otherwise . i guess vent pressure could force it up?
In any respect I have had a W114 W115 , W110 and never saw fuel in the container .

I respectfully submit the following based on my own experiences with fuel tank ventilation systems in old VW buses:

Bus fuel tanks are in the rear, in front of the engine. Later buses, in the '70s, had tank vent lines that were routed way up into the rear corners, steel tubing joined by short sections of hose. One clue that it was time to replace those hose sections was when you smelled gas after going through curves with a full tank (assuming gas wasn't spewing out past the bad gasket in the cap). When poking around looking at those vent lines you could see that the hose sections were wet with fuel, so obviously fuel was getting up pretty high into that tubing in the corners. With good hose joining the tubing sections you'd never know fuel was getting that far into the vent system (but the danged fuel cap would still spew fuel and provide a nice "eau de gasoline" for you and your passengers!).

Different vehicle for sure, but the same thing applies to our vintage M-Bs - fuel moving around in the tank will push itself into the vent system. When it works properly we never see raw fuel or smell it, ideally.

[Idle]

These allow air and fumes to vent both ways, both in and out. Without them as you pulled fuel from the tank the tank would collapse.

It helps to think of this canister as a buffer of sorts. If you just had a line to the outside it could spill gas out or suck water in, such as during a rainstorm. With this canister gas can enter the can and then vent out as a vapor. And air can enter the can and vent into the gas tank. But rainwater and dirt can't climb up the hose and then drain off into your tank. I mean, it could. But it would be a rather rare thing.

By the way.... If you have ever cleaned out a gas tank you might find, after fifty years, a bit of dirt in there. How did it get there? The answer is through the vent hose, slowly.

[meltedpanda]

learn something new every day