C63 fuel leak top of sending unit filter
 

Hi guys, I’m new to the forum and recently purchased a c63. I am at a loss with an issue and i was hoping you guys can help me figure it out. I’ve attached a pic of where my fuel is leaking from. Noticed fuel smell at rear driver wheel well each time i go for a drive and after opening up the rear seats and cover to the pump i noticed fuel slowly coming from this opening. I circled the opening in red. Any ideas?? Thank you all in advance!!!
https://cimg0.ibsrv.net/gimg/www.mbw...b95edd67b.jpeg

You need to replace that unit. Happened to me recently.

Why does it leak from there though? Is it some sort of over flow or vent? What purpose does it serve? Thanks!

Mine was cracked from age and heat, etc. Not sure if some kind of epoxy or JB Weld would seal it up, but I don't like messing with gas leaks so I replaced the whole unit.

Actually I just took a look at your pic. I don't know what's up with that hole, but mine was cracked where the black tip from the green hose meets with the white plastic.

Thanks for your feedback. Yeah i have no clue wtf that opening is for. Hoping someone can tell me. I was thinking to put a rubber cap over it temporarily till i can make the time to get to the dealer. Car runs perfectly fine but no clue why it’s leaking from there.

I'm curious to know what that hole is for as well. Just be careful with the fumes. I had a lot of gas pooled in that recess where the hose plugs in. I was shopping for a new car while waiting for the part to come in, just in case, lol.

Hahaha yeah it’s not too bad but still a gas leak.

The way that hole piece is shaped, it does seem like some sort of an overflow, but I dunno.

That’s what I’m thinking. Some sort of overflow or worn filter indication.

W204 C63 Fuel Leak at Sending Unit
 

That nipple that is leaking fuel is for a fuel pressure sensor that's used on the non-AMG C Class cars. It fits in the nipple with two o-ring seals and is held in place with a wire clip.

I'm wondering if this part will fit into the C63's sending unit and seal the leak? I think it would. The probe on the sensor may be a bit long. Even if it is, I don't think it's a problem. Here's why. As I was cleaning the nipple with a Q-tip dipped in acetone, and without pressing very hard, the Q-tip pushed through the plastic. It would be much easier than replacing the sending unit, cheaper too.

I repaired mine with JB Weld epoxy and it seems to be holding up well. I recommend C63 owners do this proactively before a leak starts. Just be gentle with the Q-tip
https://cimg3.ibsrv.net/gimg/www.mbw...018b5b5e1f.png
Fuel Pressure Sensor
https://cimg6.ibsrv.net/gimg/www.mbw...f076826dcd.png
Sending Unit With Sensor (C350)

Yes you are absolutely correct.

Since I make Mercedes fuel tanks for a living, I have somewhat an idea how they are put together and the differences between models.

That hole is usually pugged and then pierced through with the sensor when a sensor is installed.

Using a sensor to plug it would be the easiest solution.

I would not recommend any jb weld weld or some other putty. The heat which is created during hardening could crack the POM.

The cheapest solution would be some sort of boat plug if they come in that small diameter.

There is no need to do anything preventive other than replacing your gas cap.
the only reason why the port started leaking is because the fuel system had a too high of a pressure and the plug broke out.
that could be caused by not functioning roll over valves or not venting gas cap.
nothing can be done about roll over valves besides replacing the whole tank.

sventastic82, thanks for the reply.

So, the gas tank can be damaged and leak if the gas cap is bad? That's scary. Can the gas cap be tested?

On mine the access panel gasket was out of place and allowed fuel vapors into the cabin. I don't like to think what would have happened if I had lit a cigarette while driving. This is something MB should do something about. This is not an isolated problem. Please, if you have experienced this fuel leak, file a report with NHTSA at https://www-odi.nhtsa.dot.gov/VehicleComplaint/

If you scent gasoline in the cabin, or by the left rear tire, have it checked without delay.

Wil

The gas cap is vented towards the outside, if that vent is blocked the system will find another way to vent and in your case it could have been that port but only if that port was damaged or too week in the begin with.

Nothing would have happened if you would have lit a cigarette. The fumes are not even enough to be ignited by anything.

The leak isn’t even severe enough to cause anything besides smelling it. The biggest concern would be if the car rolls over in a accident and actual fuel would leak constantly. Under normal operation you would get occasional small leaks by the fuel sloshing around.