Fuel tank overflow?

[Artkez]

I'm thinking I filled my gas tank too much, but now its scaring me.

 Right after I got home from a full fill up, I noticed quite a spill on my garage floor. Looking underneath the car it appeared to be coming from the forward and top part of the gas tank, definitely not from any hoses or any leaking. The dripping stopped shortly and everything was ok, but it was a noticeable amount.  Definitely no leaking overnight .

Next couple of times I drove the car, same thing happened. Another interesting thing is that before I get to the garage, I stopped parked on an incline uphill and there is no leaking. the second I get up on the curb and on a flat surface, the slight leaking occurs.

I even siphoned one gallon out of the tank, and its still happening.
 
Where is the overflow coming from? How do I get it to stop?  What areas can gas tanks leak from? It definitely doesnt seem to be a crack or hole because then it would be consistent.

[Pawel66]

I would probably start with removing cover of the fuel level sensor inspection hole in the trunk floor and take a look there. Chances are fuel level sensor gasket is not holding or the vent pipes hoses are not sealed.

Hope it is not tank rusted through…

[rwmastel]

Have you read this?  If you're not familiar with details of the tank system, here's plenty of info.
https://www.sl113.org/wiki/Fuel/Tank

Do you have any history of maintenance on the fuel tank system?

Are you a DIY person?
- If so, that link and replies here from members will help.
- If not, there are many members in the LA area, perhaps one could help in person.  Worst case take it to your trusted mechanic.

[Artkez]

great info, ill definitely read up on it! would love a suggestion of a great mechanic in LA, close to Hollywood area

[Artkez]

so the fuel appears to be leaking from the forward and upper part of the tank, its not a significant amount since the fuel level has gone down to about half a tank. ive been driving the car a little bit and not noticing anything major, but today after about 30 minute drive, i took a look under the car, noticed some small drips, and a little bit of dripping fuel onto the hot muffler tube which was vaporizing.

very scary, I feel like this could ignite and cause a fire or a big problem!

what is going on here? something must be wrong with the vaccum or a pressure buildup?

one thought was that there could be an issue with the gas cap. I do have the proper locking gas cap. When I got the car the gas cap had a rubber seal and I couldnt get it to turn all the way. I changed the rubber seal to the proper cork one, and the cork one made the gas cap easier to screw on fully. Is this a problem? is there an issue with the venting of the gas cap? I drove it with the gas cap off and didnt notice any drips after?

is the gas cap supposed to be vented or non vented?

[66andBlue]

"unvented"
https://www.sl113.org/wiki/Fuel/LockingGasCap

[Artkez]

have I changed something buy putting in that cork gasket? did that make it not sealed properly?

[Pawel66]

When fuel is leaking from the filler cap, you see it there immediately.

In my opinion, even though I am not an expert, I would not drive the car until you identify where it is leaking, if you say it is dripping on the exhaust.

When you say "forward part of the tank", I assume it is forward of the car.

Easy access places to look for leaks:
1. Have you checked the space below the fuel level sender inspection window? that was the first one.
2. Vent lines
3. Filler - you have to unscrew some screws to remove to cover, not very complicated
4. Fuel lines on the left side of the tank - you said they were dry

The first check is the first two points, IMHO.

[Artkez]

Good call!

I feel as though its coming from the venting system some how. It seems to be dripping from the area under the passenger seat basically.

I did look under the cap at the fuel sending unit and did not see anything unusual there

[Bonnyboy]

Did you confirm that you don't have holes in the top of the tank.  A lot of crud gets in there and if it gets wet it stays wet.   

I had just a few rust holes on my tank and a new tank solved it.   

[Artkez]

how can you check?

[Cees Klumper]

One test is to apply some air pressure to the whole system, like SMOG places do on older cars. The air escaping will point to where there may be holes.

But if the leak you are seeing is from the area "under the passenger seat" then that might point to a leaking fuel / fuel return line.

Best would be to, with engine cold, turn on the ignition which will activate the fuel pump and with your symptoms, it would appear that you should be able to see where fuel is leaking out. Worst case, you may need to drop the tank to inspect the top for any pinholes etc, if you can't locate the leak another way.

But, there should be 0 leaks in this system.

[Pawel66]

Good call!

I feel as though its coming from the venting system some how. It seems to be dripping from the area under the passenger seat basically.

I did look under the cap at the fuel sending unit and did not see anything unusual there

Then rock the car, follow the smell, check the other places mentioned, that is what I would do. Indeed chances are you have rusted holes in the tank.

[Artkez]

It doesn't appear to be happening all the time, but at specific times like the end of a drive. That's what is making me think that pressure is building and causing this gas release

Just for good measure I ordered a new cork gasket for the fuel sender and will replace that. I really dont think theres any pinholes in the tank, but I will evaluate that!

[Artkez]

One interesting thing I've noticed is that my car doesnt appear to have the venting funnel under neath the car, is this found on 280sls? where can I find this part?

[TJMart]

One interesting thing I've noticed is that my car doesnt appear to have the venting funnel under neath the car, is this found on 280sls? where can I find this part?

The 280SLs do not have the venting funnel if you have the emissions system. The Vapor tank is located in the trunk and the tank vents into this from the filler neck of the gas tank.

[Jonny B]

Arthur,

I found this thread that speaks to the fuel venting system, with a diagram from the parts/service book.

https://www.sl113.org/forums/index.php?topic=23943.msg171572#msg171572

There is an explanation in the technical manual - referenced in the above thread.
Go to the tech manual, see listing for "Fuel System", the bottom three items listed under "Components" will give you a explanation of the two different systems and the workings.

[Artkez]

Just a thought.. could switching to a vented fuel cap bypass this system and solve the problem temporarily?

[Jonny B]

I did a bit of searching (used the three words "vented non venter" without quotes. Got a bunch of hits, but the first page was enough to get a feel for this.

Appears as a stop gap the vented cap can work, just keep in mind that it might leak some fuel out and that there will be a gas odor in the garage.

[Artkez]

well looks like the original idea of the leak coming from the fuel sender was spot on!

I had checked under that cap in the trunk floor, and saw a dry area... but of course i checked it long after the last drive and the gas leak had since dried

but today i decided to go for a drive and check that spot again and found it leaking like a sieve around the fuel sender. needless to say a new cork gasket is on its way! hopefully this solves it

[Pawel66]

Goo you spotted this!

Be careful when undoing the holding nuts not to tear off the studs.

I put some sealant on both sides of the cork (maybe not necessary). Sealant that is good for gas, not all of them are.

Observe the precautions related to work with gasoline. Especially if your tank is full - fuel may spill out through the sensor opening.

If you have the tube type fuel level sensor, pull it up very slowly as it is full of fuel that drips from it very slowly and it will spill when you take the sensor out to replace the gasket.

[Artkez]

wouldnt you know it, i took out the fuel sender and the old gasket must have disintegrated into thin air.... or it never had one!

I cant believe I did not notice this problem earlier. will update when the new one comes in and all is sorted. thanks for all the help!

[Artkez]

just wanted to give a big thank you to the contributors of this post who steered me in the right direction, especialy pawel66. I was able to install the new gasket easily and it solved the problem perfectly! i also took the time to replace the 4pin socket, which the previous owner had done a DIY repair on with a zip tie and some silicone. some photos to show the journey here

the first photo shows the fuel sender as I discovered it. I stuffed some paper around it which got soaked in gas after i drove around (this paper started off with a brownish color, not white) . the last photo shows the new paper I put back there dry as a bone with the new gasket!

[Artkez]

I also took a look into the gas tank from this top hole before I replaced the fuel sender. I took a real deep look, and was unsure about what I saw. what do you think about the state of the interior of the gas tank? Is it rusted inside or is that normal?

I will note that I believe there were issues with the fuel pump that must have gotten clogged up, but since then I have installed a clear inline filter between the tank and the fuel pump. I notice that It picks up some particles, but nothing crazy and my current plan is to change that out frequently.

[Lori]

Yes a little rusty but not too bad.  Have you replaced the screen filter on the bottom of the tank?  That will catch a lot of those particles as well.  You will notice more sediment in the inline filter if you let your fuel level go below 1/4 of a tank as it will draw fuel from the bottom at that point.  Mine was much worse