Fuel smell from trunk 280SL

[CromeYellow]

I read all the related threads I could find which is why I knew where to look.

Mine is the model with the evaporator tank on the driver's side of trunk.

Starting with where the fuel smell is apparently NOT coming from,

the fuel pump is new, the fuel tank itself is also new, and all the lines under the car seem fine with no observable trace of gas from underneath the car, including while it is running.





Also the fuel sensor I don't believe there is evidence of gas leaking there, and no gas smell coming from around there either



As far as that evaporator tank on the left


all the lines to it seem solid, and no gas smell there around the evaporator tank itself.







One of these metal covers is misplaced, but I don't think missing that metal cover would make a difference? on this model because I have the big evaporator tank on driver's side and no funnel pushing fumes out by the exhaust.




Where I do smell some gas is here




around the area of those two lines, coming out of the tank headed to the evaporator tank, but the lines aren't loose, the connection seems the way they are supposed to be.  I actually pulled the two lines out and reconnected them no observable difference in connection fit. 

The actual connection hose to the fuel tank seems solid. 

But that is the only area I can smell residual gas.

I hesitate to disconnect the lines at the other end at the evaporator tank to blow through them to clean them out because they seem so solidly connected, and I can't see any breaks or issues with the two lines between the evaporator tank and fuel tank.

The mechanic is willing to look at it again gratuit (he said that one of the vapor line connections was loose previously, not sure which one will find out), but then I'd want to tow the car to him which is over 100 miles away.

There is pretty much no gas smell while driving, but after stopping it is there, in the trunk and also can float into the passenger area such that the smell is observable when getting back into the car after parking it for a bit.

On the drive where observed the gas smell after driving the car for some miles (about 70 total) the car started the trip with a completely full tank.

[roymil]

You likely do have a leak to find.   However your last comment about completely filling the tank before a drive may point to a contributing cause.  Gasoline expands quite a bit when it warms and if you fill to the very top with gas from a cool underground station tank and then go for a drive there will be expansion as the fuel in the tank warms.   It has to go somewhere and will build pressure and increase the rate of any leak. 

The volumetric coefficient for thermal expansion (β) for gasoline is  950 x 10-6 /°C.  That works out to about .37 liters if there is only a 5C  (9 F) temperature change...assuming a 21 gallon tank.  Thats a lot of smell.

On a long drive you might have a larger thermal effect, and especially if you don't have the thermal shield between your rear muffler and the fuel tank.   My car had chronic issues with fuel smells in a hot climate.  When getting it running again I discovered the rear heat shield had gone missing, so the fuel tank had no protection from the heat radiating from the muffler.  No problems since I put in a new heat shield.   I'll add a picture.   I also never try too hard to completely fill it.   I think a reason newer cars route the fill point higher than older cars is to make it less likely to overfill above the venting system.

Maybe some others have some tricks for isolating fuel vent vapor leaks?   
good luck!

[RAY]

Hi Mark,  is the heat shield to the rear muffler a Mercedes part ? Not seen one before this.

[CromeYellow]

My car is a 1970 280SL.

I don't have that heat shield between the muffler and the fuel tank. 




I talked to the mechanic and he said he would be willing to install it, but he said that that muffler on my car, which is all factory, doesn't really get all that hot.  The day I drove the car 70 miles, it was mid 70s Fahrenheit outside, not a particularly warm day.

I do know that when installing the exhaust system he installed at least one heat shield, which I assume is the one under the center exhaust.

I am looking into whether there are more heat shields, including one in the front and the one in the back you mention, that may need to be installed.  He said he'll install whatever at no charge except for parts.  Is it factory Mercedes on a 280SL to have more than one heat shield involved in the exhaust system?

Anyway, the mechanic asked me to just drive the car some more days and see if there is anything else that might need to be addressed.  He said that the line that he re-connected is around the evaporator tank.  But as I mentioned those lines seem solid now and no gas smell at all there.

We talked about blowing those lines all clear, but that is something I'd want him to do, I don't want to detach those lines myself, not today anyway.

The gas I smell is around the main tube that feeds to the gas tank, but there is some spongy material there that has absorbed some gas, once that dries up then I'll be able to check that and the other areas again after driving. Plus I'll drive it with a half tank of gas this time see if that makes a difference.

Whatever gas smell is going on I don't think is coming from under the car, the fuel lines, pump, all are new and seem fine.  The smell is coming from inside the trunk I believe.

[BobH]

What type of clamp has been used to clamp the hose to the metal pipe the last picture of your first post, the picture is slightly unclear?  This should be a proper hose clamp, not sure what type would have been used originally on your car, but if it's not a proper hose clamp it's not going to give a 100% seal against fumes escaping from the joint

There are some good pictures and tips regarding the evaporator tank and fuel smells in the trunk in the tech manual

[CromeYellow]

Both slide right on and off and both hoses have a plastic cable tie on them.  I supposed I could remove that cable tie or cut it off and put a new one on there and tie it tighter.  Or use a proper hose clamp, if you're referring to an adjustable metal one?




When I slid either one off I could smell the gas for sure coming out of the metal fitting.  These are 1cm rubber hoses.

The rubber hoses in turn connect to the plastic tubing that goes on to the evaporator tank, and that connection is tightened with a plastic zip tie too, but that connection seems very tight that tube is not coming out.

[BobH]

Cable ties are never going to provide a 100% seal, needs to be proper metal hose clamps, best check other hose joints in case these have been used elsewhere

[CromeYellow]

I'll get a couple metal clamps for that connection, rubber to metal, but as as noted above the plastic zip ties that tighten the short length of rubber tubing round the plastic tubing that goes on to the evaporator tank seem to provide a very tight seal.



Anyway at the moment the only area I smell gas is there, so it's worth a try to tighten those rubber to metal connections and drive the car again.  That elbow fuel line to the tank itself is brand new and no evidence of leakage.  Thanks! for the suggestion about the metal clamps.

[Cees Klumper]

"The gas I smell is around the main tube that feeds to the gas tank, but there is some spongy material there that has absorbed some gas, once that dries up then I'll be able to check that and the other areas again after driving. Plus I'll drive it with a half tank of gas this time see if that makes a difference."

I think you found the source of your problem - and I think you will find that it will not be drying up, unless the material got soaked in gasoline as a result of the tank being completely full - but a full tank should still not mean you will have a leak. I always fill my tank up all the way and I never have any gass smell in the trunk including on hot summer days. I also do not have any additional heat shields between exhaust and tank. There is some leak that is causing this.

[Peter van Es]

There is also a cork gasket around the fuel sender. If you fill your tank completely full, you may find that gasket getting soaked, and contributing to the fuel smell.

Check if your fuel sender is mounted correctly, the gasket in one piece, and not wet with gasoline.

[Alex D]

Agree with Peter, check the gasket it may need replace.  I was driving with the top down and kept smelling gas, no leaks smell was so bad I was nauseous and to pull over.  After checking for leaks again, discovered it was the fuel sending unit gasket.

[Pawel66]

When you fill the tank full and then knee on both knees on the tank floor, you will very quickly see if the sender gasket holds.

[rwmastel]

ChromeYellow,

How do you get so many pics in one post? Are you pointing to hosted pics in the Cloud?  When those pics go away (ultimately, we all eventually go away) then this thread will be much more difficult to understand, and less helpful to others in the future. 

To anyone,

"there is some spongy material there that has absorbed some gas"

What is the spongy material?  A spacer between trunk and tank?  A seal for the filler neck on the tank?  Something else?

Understanding what that part is might help us understand where the leak is.

Yes, I also believe metal hose clamps should be used.  And, please ensure all lines are clear, specially the line coming out of the fuel tank where the venting process originates.

[CromeYellow]

I'll re-check the fuel sensor area after filling the tank full, but there is no sign of gas leakage or any smell in that area.

I am not sure what this means?

When you fill the tank full and then knee on both knees on the tank floor, you will very quickly see if the sender gasket holds.

Do you mean kneel inside the trunk on the right side?

First I'll add a couple of metal clamps to the vapor lines coming from around the elbow gas tank connection.

With the carpet and liners installed it did seem like the smell was coming more from the left side of the trunk, but maybe not.  It is puzzling how smell was coming up through the carpet at all with the liners underneath, but I suppose vapor gets around.   

please ensure all lines are clear, specially the line coming out of the fuel tank where the venting process originates.

I didn't want to detach the lines at the evaporation tank because they seem so perfectly secure, and I'd have to do that to blow air through them.

What is the spongy material?

That is it there on the left


I use imgur to host/post my images.  It is an account that will outlast me unless they eliminate free accounts.

[Pawel66]

Yes, knee inside the trunk or firmly press its floor. I know it sounds odd, but that is how I figured I had a leak through the sensor opening. Trunk floor presses on fuel tank under load and this may reveal a lot.

I think that for the smell it does not have to be gasoline leaking out of the tank. It is enough if the vent lines are not air tight - there are vapors inside, if they get free through those vents - you will smell it like gas. I am 100% sure the plastic loom ties do not hold your vent lines tight. That would be the first step I would do - replace them with nice Norma or norma-like clamps and see if the smell is still there.

[Peter van Es]

I use imgur to host/post my images.  It is an account that will outlast me unless they eliminate free accounts.

Famous last words... check some of the earliest posts on this forum where people used PhotoBucket (https://www.sl113.org/forums/index.php?topic=15857.msg139731#msg139731), Flickr (no longer free) and numerous other photo services -- now deceased.

There is a very good reason we recommend people to upload photographs to this server...

[rwmastel]

That is it there on the left

Yes, but what is it?  There are blocks of foam (or some other material) that Pawell66 mentioned that fit between the trunk floor and fuel tank.  Is it one if those?  Or, is it some sealant material that is supposed to control fumes, or fuel spillage, or something?  Maybe it is meant to be damp with fuel by design??  If anyone knows what this is, please comment.

[BHap]

The foam in the picture looks like a sealing ring between the tank and the body. #19 in the attached pic from SLS website. Probably not relevant to your leak.  The evaporation system is designed to be under slight pressure before fumes are released from the driver side wheel well area. There is a round valve that releases pressure at a certain point.  Two things I would check are the lines to and from the plastic bottle where they connect to the tank and also the gasket for your gas cap. When you open your gas cap after driving there should be a small amount of pressure which will tell you that you don’t have any leaks. I would suggest changing the rubber lines going onto the fittings on the tank with fuel grade hose. If what is there is not fuel grade, it may have broken down and be the source of your gas smell. I think the rubber hose is fairly short and connects the fittings on the tank to hard plastic lines that run to the plastic bottle on drivers side of trunk. I don’t think the bottle and lines are available, nor was the check valve when I installed a new tank several years ago.

[Lorsar]

I have #19 around the filler neck at the side of the trunk not the floor.  Plus the foam is not the same. Looks like maybe a homemade trunk pad

[CromeYellow]

I got around to driving the car again.   

In the meantime I did attach these metal clamps.



I drove the car about 10 miles, filled the tank completely, parked it, got into the trunk and put my knees everywhere pressing hard, no fuel leak nothing.  No gas smell.

I drove it another 10 miles back to home, into the garage, checked the trunk again, no gas smell.

What I did notice after putting it into the garage is bubbling noises coming from the vapor tank

https://youtu.be/ES3_paZSB38

but no gas smell.

I'll take it for a longer drive and check again.

[Benz Dr.]

I think you're using the wrong vent hose. It has to go on tightly. I believe they used the same line as the older diesel leak off lines.

[CromeYellow]

As far as I know, all lines are original.

I did not experience any gas smell when I drove the car yesterday, so maybe clamping down those hoses with the metal clamps solved the problem.

Just wondering about the bubbling noises I posted the YouTube video
https://www.youtube.com/watch?v=ES3_paZSB38
 of in the evaporation tank - is that normal?  I suppose something has to be going on in that tank for it to be functioning and I suppose bubbling sounds are the by product.

[rwmastel]

I have #19 around the filler neck at the side of the trunk not the floor.  Plus the foam is not the same. Looks like maybe a homemade trunk pad

Yes, Lori.  That is not part #19 in your pic.  That is part #Homemade.

[rwmastel]

Just wondering about the bubbling noises I posted the YouTube video
https://www.youtube.com/watch?v=ES3_paZSB38
 of in the evaporation tank - is that normal?  I suppose something has to be going on in that tank for it to be functioning and I suppose bubbling sounds are the by product.

Are you brewing coffee in there?   

[Pinder]

I had a similar gas smell and on my 1970.  after chasing all the lines it was fixed by new rubber and clamps under that cover shown in the pictures (ones with zip ties) there is no way i can see zip ties will produce a seal under pressure. the hose clamps should do the trick.