CarTalk.com Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Intermittent fuel leak

We have a 1995 Mercedes E320 with 106,000 miles. Recently we have been experiencing a very unusual problem. One afternoon my son was backing out of the garage when I noticed liquid dripping from under the vehicle just forward of the right rear wheel as he drove away. I figured it was just water and didn’t give it any thought. A few days later as he is driving away I notice the liquid, which seems much more this time, coming from under the car. I follow the liquid trail in the driveway, smell it and find out its gasoline. I schedule a shop visit. They removed the metal shroud that protects the fuel pump and filter, put it on the lift, started it up and find nothing leaking. It seems when the cat sits idle in the gartage for an extended period of time when it starts up the gasoline comes pouring out from somewhere under this metal shroud. Yesterday when we started the car the garage floor was covered in gasoline (about a gallon). It seems to be getting worse. Does anyone have any thoughts on what it might be. Any comments would be appreciated.

Point to consider: warm/hot fuel/coolant/tranny fluid lines expand and contract when cold.

Perhaps that’s why the gas leaks only when the line(s) are cold. Loose or split fitting?

I’m wondering how the evap system is on this car, especially the charcoal canister. I had a problem where I could smell gas when the car was just started and running, but couldn’t find a leak. After some investigation and a handy SRM, I found that the mechanic had put the canister’s vent line to a non-vacuum source after a service to clean the throttle body. The charcoal canister was collecting gas fumes from the tank, but not getting purged at all. Putting the lines on correctly fixed the problem.

I’m just guessing, but maybe the charcoal canister or other part of the evap system is damaged, and gas fumes from the gas tank are escaping and causing the leak. Just something to consider.

We decided to take the car to the shop once again. We stopped for gas. The gas cap was on but not that tight and I could smell gasoline. When I opened the gas cap I noticed that the filler neck and cap were wet with gasoline. I never noticed this on any of our other cars. We filled it to 3/4 of a tank. The next morning when we started the car some gasoline was starting to leak on the garage floor. This time after looking under the car I opened the filler door and say gasoline coming from under the filler cap. It was flowing down the outside of the filler tube and down the overflow tube. It seems that it is being pushed out of the gas tank by pressure. Does this make any sense. What could be causing this? I am really confused!!

Sounds like a bad gas cap. The seals can go bad. Buy a new cap at the dealer (yes, $$, but you want it right). Do not park it inside your garage until you get it fixed, gasoline fumes are explosive.

I can’t believe you’re continuing to park this thing in your garage.