85 300D Fuel Tank Vent?? - PeachParts Mercedes-Benz Forum

tobybul · #1 06-30-2006, 12:07 PM

Can someone please point out where the fuel tank vent is on this vehicle? My overflow hose is dripping from supposedly the tank getting pressurized and the vent may be clogged so fuel may be "venting" thru the fill cap and dripping thru the overlow hose. Is this possible?

1983/300CD · #2 06-30-2006, 12:27 PM

Quote:

Originally Posted by tobybul

Can someone please point out where the fuel tank vent is on this vehicle? My overflow hose is dripping from supposedly the tank getting pressurized and the vent may be clogged so fuel may be "venting" thru the fill cap and dripping thru the overlow hose. Is this possible?

By "overflow hose" do you mean the hose from the drain inside the fuel door? That hose goes straight down and drains under the car. You can get a buildup of pressure from the fuel heating. The vent nozzle under the car on the driver's side will allow air IN to the tank without much restriction, but air OUT of the tank needs to build up a PSI or two before it vents. Not exactly sure why, but that's the way mine works.

The condition of fuel getting "blown" out of the filler neck seems almost impossible. The cap is sealed for one. If you get a woosh, you know it is holding the pressure. It is also the highest point in the tank, and fuel follows gravity. If you drove on the two passenger wheels like they do in the movies, then you might have a shot at it.

tobybul · #3 06-30-2006, 12:46 PM

Quote:

Originally Posted by 1983/300CD

By "overflow hose" do you mean the hose from the drain inside the fuel door? That hose goes straight down and drains under the car. You can get a buildup of pressure from the fuel heating. The vent nozzle under the car on the driver's side will allow air IN to the tank without much restriction, but air OUT of the tank needs to build up a PSI or two before it vents. Not exactly sure why, but that's the way mine works.

The condition of fuel getting "blown" out of the filler neck seems almost impossible. The cap is sealed for one. If you get a woosh, you know it is holding the pressure. It is also the highest point in the tank, and fuel follows gravity. If you drove on the two passenger wheels like they do in the movies, then you might have a shot at it.

Thanks for the input. I am not totally convince myself that this was the cause. Just feedback from one of my other posts. I did fill the day b4 this occurred and very likely I did not close cap tight...or cap my be getting bad? Yes, it is drpping from the hose from inside the fuel door. It was a bit damp inside behind the fuel door the first time I chked this prob.

MattBelliveau · #4 06-30-2006, 01:27 PM

Mine is on the drivers side of the car, and I think it's in front of the trailing arm (I replaced my line a year ago, so I'm just going from memory). It will look like a hard fuel line with a spigot looking thing at the end of it, and faces the rear of the vehicle.

#5 06-30-2006, 02:15 PM

According to the drawing in the Haynes manual, the vent comes off the center top of the tank and goes left, and then down to the left rear of the tank, near the fuel gauge sender.

tobybul · #6 06-30-2006, 10:50 PM

Looks like the cause of the drip on mine was a loose or untightened fuel fill cap. After I tightened it the problem stopped.

dazsa · #7 07-01-2006, 10:51 AM

My vent line under the car is plugged, so I am leaving it unhooked where the vent line comes out of the bottom of the trunk to see if it fixes my vacuum build up.

Don

dieseldiehard · #8 07-01-2006, 01:22 PM

Quote:

Originally Posted by tobybul

Looks like the cause of the drip on mine was a loose or untightened fuel fill cap. After I tightened it the problem stopped.

BTDT
My wife put the cap on her '83 300D on sideways, half of it was tight, mis-threaded like it was fuel was gushing out on turns, made a mess on the RR fender. Oh duh!