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mattsuzie 03-26-2000 10:38 AM

Hello. I have a 90 300 SEL and I smell gas inside the car. My mechanic told me it was a faulty gas cap so I got a new one I still smell gas. I see no leaks anywhere and/or on the ground.

The smell is strongest when I lift up the cover for the spare tire. Could there be a hole on the top of the gas tank? Would be unlikely to be there, but cannot think of anything else.

It seems like the vapors are going in the trunk, since there is no ventilation there, it then seaps inside the car.

Oddly enough, it seems like the smell temporarily goes away when I start the car, especially if I put the air on. I have not lost any gas mileage that I can notice, so leak, if any, must not be that big. The smell is terrible though.

Do you have any advice? Please help.



stevebfl 03-26-2000 11:16 AM

Fuel smells can be the worst. A small amount can stay with you.

Place the car on a lift and view all the rubber hoses in the area around the tank exit,fuel pumps, accumulator etc. View also the return hoses.

Does it only smell with a full tank. Try keeping it at half for a while (after you can't find visual evidence - look for staining it will still smell long after dry).

If it makes a difference full, you can expose the tank sending unit (and seal) through the first aid kit (I think).

One other possibility before you pull the forward trunk panel. In the gas flap area there is a drain hole for rain water to exit. This pipe is metal at both ends but passes through the trunk with a rubber or plastic hose which if disconnected can pass overflow fumes and/or leakage right into the trunk.

Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

mattsuzie 03-26-2000 12:06 PM

Thanks Steve.

The smell occurs at all levels in the tank. I did notice that there are 3 passages for the fuel to go in the gas flap; 1) obviously the round hole in the center that goes to the gas tank 2)the small hole on the bottom lead by a black plastic hose to the ground and 3)an opening just above the center hole to the gas tank (I do not know where this goes to)

I just filled up the tank this morning and I watched the gas slightly overflow, 99% goes to gas tank in center hole, some went to the bottom hole and some went to the "opening" above the hole. I watched it go to all 3 places. I could not know what I am talking about, but that is what I saw.

9 months ago, I had the following replaced: fuel governor and fuel pump and the hoses look good, but who knows? Why do you think the smell inside the car goes away when it is running?

Does the 300 SEL have a fuel vapor plastic expansion tank like I have been reading for the SL's? I heard that they leak.

I was confused about what you said about the gas flap area. I noticed a black plastic hose coming from the gas flap area. I do not see it passing through the trunk. I do notice when I overfill the tank , some gas comes out of that hose, but I have been slightly overflowing my tank for years, only now have a smelled a strong smell of gas from the back.

How can I smell gas in trunk, but see no leak. Run car and look under car and no leaks any where, but car smells like it will explode in trunk.

Thank you very much for your input.

stevebfl 03-26-2000 01:22 PM


I could be wrong about where the "rain drain" passes. If your put water
through it, all of it should come out the bottom. Pour a glass and catch
with same size glass.

As to why you don't smell it as much driving, your car is designed with
flow through ventilation. The constant changing of the cabin air takes place
with the flow as follows: in at the cowl ducts in front of the windshield,
through the interior, and out of the car through the trunk. The way it
gets out of the trunk is through doors built into the forward portions
(under) of the rear bumper (at the sides). These are visible after removing
the lining in the lower outward trunk recessions. Since the flow is away
you are in effect upwind from the smell.

If the "rain drain" isn't your problem and there are no leaks underneath, then you will need to remove the forward wall of the trunk and expose the tank. I think the fuel separator is in the tank. These kind of details I'm not so good with at home. My first activity professionally would be to
verify the whole circuit in the manual.

Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

mattsuzie 03-26-2000 02:19 PM

Thanks Steve, I think I am making progress. When I lifted the carpet on the right side in the trunk, there is gas. Gas is somehow flowing down the right wheel well after filling down inside the trunk under the carpet.

Did the water test in the drain hole in the gas filler and the water came up to the same level (used 2 clear coke bottles).

This is the kicker. Where does the fluid go in the third hole in the gas filler cap.

There are three places where the gas could go on filling

1 - Big Circle = fuel tank

2 - Bottom hole = ground

3 - Horizonal Space above Big Circle (#1) = I do not know

Hole #3 maybe is going down the wheel well to the trunk. Afraid to put water down there in the event that it goes into the tank. Does that 3rd space lead to the trunk?

Is is hard to remove the right trunk carpet, would hate to damage it to see.


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