Fuel Tank Leak

I had previously fixed a fuel smell in the boot by noticing a slight discolouration in the insulation on the LHS tank (see "New 400i Coming" thread). There was a slight crack where some numpty had hit the top with a hammer or something, and two holes drilled by an even bigger numpty - probably mounting something on the boot board. I fixed both with epoxy.
Today I get the car back from a service, and filled the tanks to the brim - the fuel smell was so bad, I almost threw up. It seemed to be from the right, so I pulled off the boot board and the RHS bumper tube. Photo coming...

 

You can see the discolouration of the coating. I have started to strip it off where I think the leak is, expecting to find a seam, but there doesn't seem to be one there. Such a complex form must have seams - does anybody know where they are? Perhaps a diagram ot picture?
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Thought there'd be a seam along here
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Can'you try a tank sealer? If you tap the lower port, you could put the tank sidewise and properly apply the sealer?

My brother bought some new uncoated tanks long ago (aluminium, flat black painted). these are in a rack 6980km away from were I am right now...could take some pics by the end of next week.

By the way what's the use of the coating?

 

I don't want to take the tank out at this point.
I really hope that I've got the problem solved by then, but a few pics would be most informative, thanks.
The coating protects the alloy, provides a bit of thermal insulation, and reduces condensation. Cold fuel on a humid day will cause condensation on the outside of the tank, which is... bad.

 

Does not protect alloy, as the "bare" tanks are painted, that's why I was considering using theses "as-is", but thanks for pointing out the condensation issue.

 

Good day,

On a side note about sealers... A colleague of mine has a friend that owns a specialty Industrial epoxy paint company and they use one of their paint products as a sealer for inside old gas (petrol) tanks for the old cars they restore. They mix the epoxy paint (2 parts), pour it into the empty tank, "swish" it around (they have minutes before the paint starts curing), then let cure for 24 hours. Effectively this seals any small pin-holes, etc that might have developed over time. The epoxy paint they use is virtually impervious to any chemicals, etc and the only way to remove it is via grinding, etc. Interestingly they have been doing this for over 20 years and have had no issues. Given that my tanks are empty I was thinking of doing this as well.

Cheers,

Sam

 

Thanks, Greg, but I can't find that thread. I'm trying to find a leak, which looks like it's along a seam from the wetness pattern, but it may be a single pinhole and the fuel has wicked through the porous coating. I'll check it again in a minute, and hopefully the wetness has contracted around the offending defect overnight. I'm hoping to seal it with a bit of epoxy.

 

Thanks Sam. I'm hoping not to get to that point! My working hypothesis is a split along a seam, but I haven't found a seam where I thought there was one, hence the call out for info. I'll keep plugging away. Hopefully plug a small hole, fill up the tank (I've drained out 60 litres), and watch carefully - all in between helping my 10 year old build his P51 D Mustang!

 

Here is the material I used.

HighmilerFormula Junior
Joined:
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413
Location:
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Full Name:
Greg
This patching compound is made by Flamemaster and is called "CS 3204 Class B Aircraft Fuel Tank Sealant". The paperwork says it meets MIL-S-8802F. The distributor and packager of this stuff is Located in Sun Valley, CA. Phone; 818-982-1650, Fax; 1-818-765-5603. I got mine from Van's Aircraft Supply in Oregon for @ $32.00 the quart..

For those unfamiliar with Mil-Specs: these are stringent specifications produced by the US Military to ensure that what they buy is what the salesman claimed it to be. Most SAE Standards began life as Mil-Specs.

Greg

 

So I've scraped a bit more for the coating off, and noticed something curious: the stain on the coating isn't evaporating, and the little bits of stained coating don't have a petrol smell, in fact they're a little oily. Maybe somebody spilled something oily in the boot 20 years ago and stained the coating that way. Maybe I've been barking up the wrong tree. So I'm going to removed the rest of the boot lining so that both tanks are exposed, and then pour the petrol back in until it's brimming again, and watch closely. Should get to it by... April

 

It's probably not much help but Marc found the source of my raw fuel smell in my 365, a couple of years ago,had to do with rubber fuel lines and breathers etc.
He tells me that yours has sustained damage in that (RH) area of the boot....something to check out.

 

If no crack in tank the next obvious source after filling the tank is the seal on the fuel guage sender. I replaced mine and now have a lot less odor in trunk.
Ken

 

Thanks, Ken - all options will be entertained. Hopefully it will be that simple.

 

Update: still looking. I have basically ignored it for a few months, but got inspired after watching an episode of "Overhaulin' ". I thought, perhaps, the breather might be at fault. So, out comes the front boot board, then drop the rear a/c evaporator, but wait! Someone's installed an amp, which blocks one of the nuts, and it's held in from above with self tappers, which means removing the rear parcel shelf trim; which means removing the rear seats and the side trims. Don't you love these things? Oh, and I haven't found the leak yet.

 

Lol! good luck

 

This is just me but I’d pull the tanks and have them sealed from the inside. What are you going to replace the insulation you have scraped off?

 

Looks like the same audio guy made the install in my car... Did not have to remove the side trims though: once the seats are removed, the shelf has enough flexibility to as to be removed without damage.

I doubt the canister is the culprit: on my car the tubing was different than the fuel hoses. These transparent hoses did age much better than fuel hoses. Maybe you've seen the photo I sent on "what did you do to your car today": The leaked gas was accumulating on the soundproofing sheets that are placed between the tank and the trunk floor. These sheets do make things worse as the gas does not find its way out and slowly evaporates in the trunk (the smell remains for ages). After removing all the hoses it was pretty clear all of them were slightly leaky, including the return lines.

My mechanic had to remove the tanks in order to put the new hoses: removing the old hoses "in situ" was easy given how damaged these were, but inserting the new hoses could not be achieved without moving the tanks back and forth. At the end of the day it was easier to take them out. Good opportunity to clean them.

 

I've got two new tanks. The bad news is that these have been stored on top of a rack for ages, so hard to access and capturing them on camera is not as easy as it seems. The good news however is that these have not been coated, so you can see (second picture) where the sheets of metals were folded and soldered.

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Here a close-up of the portion that seems suspicious on your car:

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Hope this helps.