As the title says, I can hear a bit of suction when I remove the fuel cap on my 1985 300D.

I know this is potentially a clogged vent, but is some suction normal?

If its not normal then how to i go about unclogging the vent?

Thanks

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1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

GONE but not forgotten
1976 300D 195,300 miles
1983 300D Turbo 175,000 miles

http://i42.photobucket.com/albums/e3...e485-1-2-1.jpg

Slight suction or pressure is normal. The relief valve does not maintain a "zero" pressure differential.

Perfectly normal,i dont have time right now to look up the info but it is in the shop manual. Don

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Red Green "This is only temporary,Unless it works!"

97 E300D 157000 miles
87 300TD ?141k? miles

You'll hear more suction if you're low on fuel.

Outside temperatures might also have something to do with more or less suction.

SLIGHT suction is ok. you might wanna pull the carpet/divider in your trunk and see if your tank is getting sucked in, just to be sure your slight is not more than the proper amount...

also if it is a plugged vent, it's pretty simple to look at the bell under the driver's side rear door ( I think it's under there anyway, just look under the car for tubing with a bell on it...) for mud or whatnot plugging it up.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Okay just wanted to make sure it was normal, my 76 300D never had any suction at all when i removed the cap, nor does my 280CE.

Thanks

__________________
1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

GONE but not forgotten
1976 300D 195,300 miles
1983 300D Turbo 175,000 miles

http://i42.photobucket.com/albums/e3...e485-1-2-1.jpg

My car is a W124, and I have never heard any suction when taking off the fuel cap, but I have a strange thing on the cap itself, its rust, I painted it with POR from the inside, cured it and coated it again, it still rusts.

Is this a sign of water in my tank, I regularly use startron in every tankfull.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

I think it's normal... atmosphere contains water, and it'll collect on cold surfaces... like the cap.

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

If it is the same as a 85 300sd, there is a vent pipe off the tank and a plastic two way valve that keeps liquid in the tank when you roll over and yet allows air in when fuel is pumped out of the tank. The valve is fairly easy to change as mine was plugged. Some say they have seen spider nests up their metal vent pipe that comes out by the driver side rear tire. An old speedo cable works best for running up that vent pipe. My guess is the plastic valve. If not available on this site try Diesel Giant site.