Fuel Tank Vent on W210 - PeachParts Mercedes-Benz Forum

Eggburt · #1 02-06-2006, 03:16 PM

All of a sudden my 99 E300 DT is spitting diesel. I read some earkier posts and replaced the fuel tank cap but it is still burping diesel.

I assume that the fuel tank vent is clogged but have read differing suggestions on its location and how to clear it. Can anyone offer me assistance on where the vent is located on a w210 and how best to clear it.

raMBow · #2 02-06-2006, 07:07 PM

I would be curious as to your resolution. I've replaced the gasket on the fuel cap, which has made significant reductions in this. But from time to time will find some fuel beyond the cap prior to removal, when I refuel.

Have not really been able to track exact conditions of when this accually occurs. Warm, cold engine or weather temps, or how full the tank is. Simply I do not spend that much time filling up.

raMBow · #3 02-10-2006, 02:57 PM

Seems the '99 E300DT is still burping out some fuel at some point. Spent a lot of time at home today with sick kid and have not been able to find a definitive search here. As to the location of this vent and how to check for possible blockage.

Has anyone cleared the vent?

Where is it located? If you know please be very specific.

Backed it up on some ramps and rolled around looking for some time. Two tubes coming down in front of each rear wheel well. Seems like some of these are just body drains. One small clear plastic drain under center of car and another very small vent high up over the rear differential, but it is rubber and bent like a flat thumb. Did appear to be near a metal fuel line.

Noted some rust in the top of the filler neck, but nothing on the mating surfaces for the gasket.

Suggestions would be appreciated.

raMBow · #4 02-11-2006, 10:45 AM

Thought I would bump this once, now that the weekend is here, in the hopes of input.

Eggburt · #5 02-11-2006, 11:18 AM

I crawled under the back end and located the vent. It is located next to the fuel supply line almost directly above and to the front of the rear end in the center. The vent has a flared S-shaped connector that can be carefully removed. My hands got caught a couple of times but just gently pry it off and the vent tube will appear. I, too, was hoping to get back to it today. I plan on using an old turkey baster to insert into the vent tube and 'plunge' to remove any obstruction in the line. Do not forget to replace the S-shaped cover when done.

The first thing I did was replace the fuel cap but that did not solve the problem.

My current theory,

, is that a bubble is blocking the vent line from working. Possibly due to topping off the fuel tank to get to a whole dollar amount on the pump

. I do not want to put to much air pressure into the line so I hope a few squirts with the baster will do the job.

raMBow · #6 02-11-2006, 11:46 AM

I know which one you are talking about. I'll go out and try that myself. I'll try to take a picture of it if anyone wants to find it later.

raMBow · #7 02-11-2006, 04:14 PM

Removed the rubber snorkel type item off the vent found up above rear Differential above the passenger half shaft. Used a paint can opener to easily pull it down. The space is very limited in the area.

Placed 10' of 3/8 ID plastic tubing on it. Brought that over to the fuel filler with the cap removed. I could easily blow into it and hear it coming out the vent in the fuel filler neck. No problem drawing air from this either.

Tried with fuel cap on, same story.

Started '99 E300DT and same story. Easily draw air from and blow air into system.

Any thoughts here? (No I didn't breathe a bunch of diesel vapors)

If the vent is clear how does fuel get up there and get past the gasket?

Should I put some serious pressure on it with the air tank?

Oh, said I woud put some pictures as to above. First attempt...

raMBow · #8 02-12-2006, 09:56 AM

Still trying to make sense of this.

Is there some valve that closes the vent?

Did a couple of test drives last night to attempt to determine conditions under which this occurs.

First Drive - 12 miles, normal run to town, moderate acceleration, max 60mph. Check and cap had not leaked, though some fuel was being held back behind the gasket, so when I took it off, some came out, 5 drops or so.

Second Drive - same 12 mile run, only this time (mad dash to get child's perscription before pharmacy closed), plenty of hard acceleration (3/4 only, no WOT) and 90 mph on the "home stretch". Check and some fuel had made it beyond the cap, wet inside the fuel filler door, but no puddles.

Third Drive - 170 mile run to the City (did I mention the Pharmacy was out of that medication and now I have to find a 24-hr Pharmacy somewhere in the state etc.) Interstate travel mostly 70 - 80mph. One WOT. (Wake child up at 11:45PM force her to take this nasty stuff). Quick check, put tip of finger into base of fuel filler door and tip of finger is soaked in fuel.

Ambient temperatures for the day were between 34 and 28 with light snow.

Any thoughts appreciated. (No I will not drive like Grandma to avoid this)

raMBow · #9 02-12-2006, 10:55 AM

Fuel level was between half and quarter tank only during these runs, so overfill etc. not an option.

spark3542 · #10 10-20-2008, 12:24 PM

Resurrecting this thread, it came up when I searched for e300 fuel tank vent.

I'm getting significant vacuum when I open my filler cap on my 97. Would putting pressurized air into the vent as described in this thread do the trick?

Thanks