w124 tank vent?
 

Where is the tank vent line? I get the suck when I open the tank.

According to the CD shop manual (47-0030)when operating properly the tank could have up to 50mb pressure or 1 to 16mb vacuum! So a "woosh" when you open the cap can be a normal function.To answer your question the vent is under the car on the sedan im pretty sure it on the passenger side a funny looking bell shaped thing. Don

Yep, on the sedan it's under the drivers side rear. If you follow the fuel return line where it goes back up thru the floor into the tank, the vent valve will be just a couple inches away from it. It's attached to the metal line from the tank with a short piece of hose - a pair of needle-nose pliers will work to undo the clip and let you pull the whole assembly off.

But if the car has stock tires, unless you're thinner than Twiggy, you'll need to jack the car up on that side to even get to the bloody thing. Another reason I love 205/70 tires.

Are you sure it is the suck . . . and not the blow? Also possible for pressure to build inside the tank if air is getting fed into the return line.

No but I ran a bit past the empty light and fill up was only 15ish gallons. 27mpg tho, not horrible for the way I drive.

Is there a method to test the vent. I never have a vacuum or pressure either for that matter.