fuel tank vent?
 

Hi gang,

Sorry for the noobish question, but I was just reading another post and have to ask. Since I bought my '95 E300D about 4 months ago, it has regularly made a suction sound - like breaking a vacuum seal - when I undo the fuel cap to fill up. Being new to MB and diesels, I thought this was normal, but it appears as if it is not. Others seem to suggest that there is a fuel tank vent that can get clogged and create this situation and subsequently affect fuel flow. Can someone confirm this for me? Also, anyone know where to find the vent?? Thanks in advance!

- Mark

I cannot confirm this for your year vehicle, but on the older MB's above the passenger's rear tire there is a bell shaped device tank vent. if it's clogged with mud, you fuel tank can implode. Ive seen it.

Yikes, well, I guess I better get to looking. If there is one there and it is plugged - or partially plugged, I wonder how much it has been affecting performance. I have had some ocassional nailing - wonder if this might be related.

tank,

I thought the vent exit was on the rear driver's side on the older MBs but I don't know where it might be on your car. Look for a steel line with a strange looking rubber gizmo on the end.

Plugged vent will not cause nailing. It might cause a loss of power because not enough fuel is getting to the engine.

P E H

Any idea where it is on a 1987 300D (W124)? I put a new fuel cap on the tank and still have the same problem.

-Jim

On '81 it's on left rear
 

On my '81 it's on the left rear side, just forward of the tire and inboard from the rocker panel by maybe 6". Look for a bell-shaped thing hanging straight down. Remove the bell and clean the vent tube as far as you can by pushing a wire up it.

Cool. Thanks guys. I will have a look tonight and report back what I find. Is a bit sluggish at times, not sure if it related, but sometimes I feel like I should be getting a little more power - even for a NA diesel.

Hmmm. Well, I had a look this evening but I am still not 100% sure. I am pretty sure I found the fuel tank vent. It looks to be a plastic hose that hangs down from the front-top of the tank - located on the passenger side. I couldn't see that there wasn't anything obstructing it though. I know that I am not looking at a water drain, but I couldn't confirm that it actually attached to the top of the tank.

Anyway, the more I think about it, the more I actually think that the sound I am hearing is not air being sucked into the tank when I remove the fuel cap, but rather, air escaping the tank. So, what about that - normal or not? If not, what's the deal? Either way, I guess the tank vent would have to be plugged somehow.

Could that be the drain outlet from the filler area? If it is not too cold, pour some water in the hole under the fuel cap (the drain) and see if it comes out there.

I don't have a clue where it is so feel free to disreguard me! :)

-Jim

Hey Jim, good point. But I am pretty sure it is not as all the water drains pretty much look the same and I have scoped them out before. Regarless, I plan on snaking a cable through all the drains and then up this one suspect hose to see what I get. I will keep you posted.

-Mark

I have a mild tank vacuum issue on the 1984 300SD. The tank vent tube is not blocked at the bottom. I've run wire up it about 18 inches with no restrictions and no debris coming out.

Is there a section of rubber tube somewhere on the top of the tank that could be collapsed? I presume the vent tube leads to the top of the tank.

Ken300D

I recently dealt with my tank screen and tank vent on my '87 300D. Check out this thread: http://www.peachparts.com/shopforum/diesel-discussion/209993-87-300d-tank-screen.html

Answer:
 

Yes, there is a vent valve, picture attached.

Here is the part you need.
MB# 2014760232


Item Number: 2014760232
Main Category: MB
Sub Category: Fuel System
Description: Valve...fuel tank vent...application...124, 140, 126, 201, 210
Weight: 0.100

Answer:
 

W124.133
You have the same setup/location and part number as post #13.

Answer:
 

Superseded to the part# in post #13.