help diagnose this fuel-filler overflow issue - 202
 

97 c230.....pump has been cutting off at 6-8 gallons for 2 years, worse in hot weather. I know when my car is full, and what point on the fuel gauge correlates to how many gallons it needs.

Except today, when it started dripping gas somewhere behind the wheel. Apparently overfilled. I opened the flap and there is no leakage there. This has to be related to the early cut-off issue I think. Where's the failure point? Is there a clog in the neck? I'm not sure what's between the cap and tank.

Our cars are getting to the age where cracked/deterioated hoses/vent tubes for overflow are becoming common. Maybe your's has split. Remove the plastic inner fender and give everything connected to the filler neck area a good inspection.

It is common for these cars to be a pain to fill up. I put the auto fill clicker on the slowest filling setting possible and am then just prepared to wait. It usually fills up until full before clicking off but at a slow rate. Probably a blessing in disguise. It gives me just enough time to clean all the windows plus headlights and then pop the hood to check the fluids. If it went faster, I probably wouldn't check these things often enough.

Mine clicks off at 6-8 gallons while using the low setting. I just have to keep clicking for 6-8 gallons more. You can imagine how maddening it gets.

I suppose I need to remove the wheel and the liner, and then I should have access to the components?

I don't know what I'd repair. Would one replace the filler neck?

Have you tried this? Rather than pushing the pipe all the way in, leave it out and inch or two and let the handle sag down. This way, the pressure should be able to vent through the small gap between the filler hole and the pipe. I think the problem you’re experiencing is related to the environmentally-driven new gas pump technology (that, in an effort to avoid spilling even a drop of gas) cuts off at even a hint of pressure. It doesn’t sound like there’s anything wrong with your car.

The gas leaking out under the car is what is supposed to happen if the tank is over filled. It will leak out until it goes down to the maximum level the tank can hold.

yep, done it. No difference. The only way is manual squeezing at a trickle.

So, if it's supposed to leak, that's good. I pulled up the part on eBay - it has so many vents, curves, and gaskets to make me think something is probably clogged, keeping vapors from venting out. Maybe I should just replace the damn thing.

http://cgi.ebay.com/ebaymotors/94-00-Mercedes-c230-Fuel-Filler-Vaccum-Tank-Pipe-Hose_W0QQcmdZViewItemQQcategoryZ42604QQihZ006QQitemZ160135164183QQrdZ1QQsspagenameZWD1V

What is the housing? I was expecting - drumroll - a tube.

Is this an overflow chamber? Does it hold excess fuel? Is it designed to hold vapors?

Personally I wouldn't replace it unless you could test and prove that the part was defective. Have you tried different gas stations? Our C230 has always had lots of little quirks. For the little things, it's very often been something seemingly obvious (not mechanical or electrical) that resolved the issue. For example, one day the fuel gauge stopped working. Thoughts started going through my head about replacing the fuel sending unit (is that what that part is called?) and all the labor that goes with it. I starting thinking back to what I had done differently right before the problem started. Oh yea I had put el cheepo discount store gas in the tank. Went and topped off with Exxon or Amoco and bingo the problem was fixed and it's never come back. That was like four or five years ago. Another time was the CE light. Got the codes and couldn’t figure it out for the life of me (keep in mind I’ve been through the MAS twice and know what that’s all about). Starting thinking about stupid things that would mess up the fuel pressure and delivery. I took off the gas cap and started poking around. I looked real closely at the gas cap itself and saw that the rubber grommet was starting to dry out and crack. Switched the gas tank cap from the E class wagon to the C230. Problem solved with an $8.00 gas tank cap. I don’t have any ideas for you, but I’d bet it’s something lame that’s being overlooked.

Well, as the issue has been going on for 2 years and 70k (yes, 70k in 2 years) I've tried MANY gas stations. I would say that I DON'T experience the issue at 1 in 10 stations. So, it's an issue with vapors accumulating where they shouldn't.

Back to square one.......my best guess is vapors aren't escaping, and that pretty much would have to mean something is clogged.......so wherever the vents are along the path is where I will start

I'll probably end up throwing it in the shop and paying them $90 to figure it out. I give up

I also have the same issue, on my 1998 C230 with 99Kmiles, for the past 18months.

I think I have an issue with the piping for the filler neck shifting in it's brackets. Sometimes I hear a noise form the passenger side rear wheel-well when going over bumps, anyoe else hear a noise like that?

But that is just a guess.