the 87 300TD fuel tank has an overfill dump line? - PeachParts Mercedes-Benz Forum

vstech · #1 10-07-2010, 12:14 PM

Well, I got my TD on the road, and took it to the filling station. I wanted it totally full for my economy to get calculated. however, I was not paying attention to the pump, and I dumped 5+ gallons on the ground!!! arrgh. cleanup mess, etc.
2nd week I go to fill it up and I am paying SUPREME attention to the pump, slowly dribbling fuel in to the top of the neck, and it keeps taking it and taking it.
I notice splashes under car, look down, and there is a tube that is just POURING fuel out!
arrrgh again!
I call roy, and he confirms that the 124 wagon has a built in filler neck drain to prevent overfilling and expansion of the tank!
ficacta! blankety blank!!!!
first click, off.
period.
don't fill the 124's to the top!

babymog · #2 10-07-2010, 02:31 PM

I top mine off, never dribbles, can always get to the next whole dollar.

I think that line is a vent and should have a valve on the end. Photo?

DieselPaul · #3 10-07-2010, 02:34 PM

It runs to a valve on the bottom of the tank.

vstech · #4 10-07-2010, 07:39 PM

Whunter said it's stock that way and it prevents overfilling the car. it's too dark out to take a good pic tonight, but I'll snap one and put it up in the AM...

vstech · #5 10-07-2010, 08:21 PM

I went out with a flashlight and snapped off a pic.
it drains out near the subframe mount.

Billybob · #6 10-07-2010, 08:24 PM

Quote:

Originally Posted by vstech

Whunter said it's stock that way and it prevents overfilling the car. it's too dark out to take a good pic tonight, but I'll snap one and put it up in the AM...

"it prevents overfilling the car" what does that mean? By dumping fuel on the ground! That makes no sense at all, the prevention to overfilling the tank is the pump's fill nozzle shutting off when the filler neck is full! Don't you think that there would be a mention of such a feature in the operator's manual, the FSM, the EPC, I thought the fuel tank and its plumbing was designed not to leak fuel even in a rollover!

Sounds like you've got a failed connection or a deteriorated hose that is leaking fuel once a certain level is attained in the tank. Possibly the large diameter vent hose that runs between the tank and the filler pipe

Billybob · #7 10-07-2010, 08:28 PM

Quote:

Originally Posted by vstech

I went out with a flashlight and snapped off a pic.
it drains out near the subframe mount.

That looks like it could be the drain for the passenger side compartment behind the rear wheel. Where the jack, first aid kit and folding triangle are stored. The large vent hose and the filler pipe transit that compartment.

vstech · #8 10-07-2010, 08:29 PM

I think I will be pulling up the carpet and inspect any hoses going to the fuel tank.
this line looks like a drain for the wheel well or something... I doubt fuel is supposed to be there...

layback40 · #9 10-07-2010, 08:32 PM

Most cars have some sort of tank vent. I cant get my w124 to over flow and I fill it & shake the car & fill more till all the bubbles are gone. We have our own gravity fill from an over head tank, no auto shut off. Maybe some do overflow & others dont. One day I must put a little compressed air in the tank & listen for the vent.

Billybob · #10 10-07-2010, 08:40 PM

Quote:

Originally Posted by vstech

I think I will be pulling up the carpet and inspect any hoses going to the fuel tank.
this line looks like a drain for the wheel well or something... I doubt fuel is supposed to be there...

I don't think you'll be able to see much under the carpeting there is only a plastic cap about 2 1/2" over the fuel level sender access hole. You might be able to see if fuel is/has been flooding the top of the tank though! If it's the vent hose I'm pretty sure you'll be dropping the tank to get to the fitting at that end! A mirror from underneath and outside of the tank might let you see something, I think there is a grommet where the vent hose passes through the chassis into that behind the wheel well compartment. The other end of the hose attaches to a bib on the filler neck in there. When dealing with the tank you attach the vent hose to the tank then lift it up into position threading the filler neck and vent hose through the chassis.

I'll venture to say your mileage ought to increase a bit once you fix this!

vstech · #11 10-07-2010, 08:44 PM

I went out and opened the wheelwell area, and it's dry, no sign of fuel in there. got under there and fully inspected the area, and it is indeed a vent built into the fuel tank. it's coming down the side of the tank. it's deep inside the frame of the vehicle, nowhere near the wheelwell of the car.
while digging around I discovered a HUGE Black widow!!!
methinks I'll be spraying my car before doing too much wrenching on her!

layback40 · #12 10-07-2010, 08:56 PM

John,
"Huge black widow" ? What are you doing with your girl friend under the car !!

vstech · #13 10-07-2010, 09:08 PM

Quote:

Originally Posted by layback40

John,
"Huge black widow" ? What are you doing with your girl friend under the car !!

Sorry, I can't help it, I'm old, I forgot where I stashed her...

vstech · #14 10-08-2010, 11:23 AM

Quote:

Originally Posted by Billybob

I don't think you'll be able to see much under the carpeting there is only a plastic cap about 2 1/2" over the fuel level sender access hole. You might be able to see if fuel is/has been flooding the top of the tank though! If it's the vent hose I'm pretty sure you'll be dropping the tank to get to the fitting at that end! A mirror from underneath and outside of the tank might let you see something, I think there is a grommet where the vent hose passes through the chassis into that behind the wheel well compartment. The other end of the hose attaches to a bib on the filler neck in there. When dealing with the tank you attach the vent hose to the tank then lift it up into position threading the filler neck and vent hose through the chassis.

I'll venture to say your mileage ought to increase a bit once you fix this!

well, I'm computing (taking into account the fuel I dumped on the ground ) about 30mpg... sounds fair to me.
this vent that none of your cars seem to have concerns me. should I drop the tank and visually inspect the top for damage/failed hose?

Bio300TDTdriver · #15 10-08-2010, 11:36 AM

Quote:

Originally Posted by Billybob

That looks like it could be the drain for the passenger side compartment behind the rear wheel. Where the jack, first aid kit and folding triangle are stored. The large vent hose and the filler pipe transit that compartment.

I agree, that is for water, not fuel.