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Thanks again! I'll have the mechanic hoist it again and have a good look. For liability if nothing else, I'll probably have to find a lift I can borrow and do

Thanks again! I'll have the mechanic hoist it again and have a good look. For liability if nothing else, I'll probably have to find a lift I can borrow and do the job myself, but first I'll make sure the entire exterior of the seam is accessible while the tank is in place. I never saw a drop (re drips) until just a month or two ago -- when I parked for a day over some fresh snow. So, it may be too late, now, but it's worth a shot. I also can put 8 gallons into an empty tank without the problem manifesting. If I can somewhat seal and protect the seam from the exterior, per your suggestion, I can also stick to partially filling the tank, most of the time. The car only has about 135K on it, and the interior is pretty much spotless while the exterior has had only a couple of nascent rust spots that I've actively kept under control. Until this winter; I had to switch detailers and the new one seemed to create paint chips rather than mitigating them. I used to do most of this work myself, but health has had me seeking help. Anyway, it really seems worth getting the extra year or two out of it, if I can. As for the alcohol blend fuels, I was aware that they help significantly in keeping the tank "dry". It's been my understanding that they may also contribute to the lower instances of "vapor lock" that we see, these days. At least, at my mild altitude and (mostly) non-extreme environment. Applying an exterior coat does sound like an interesting idea. One concern I would have, is whether if and as it deteriorated, it might trap moisture and corrosives next to the tank, turning from protectant to trap and accelerant. I used to rinse my undercarriage extensively each spring, after the last of the salt was washed off the roads by rain. The last some years -- again, health -- I've gotten... well, I guess I could be self-deprecating and call it lazy. That may have made things worse, but 18 years of Chicagoland winters doubtless bear the bulk of the responsibility, regardless of such mitigation efforts. And I didn't have this car for the first 10 or so years of its life; the damage was already well underway.

Baeocystin 9y ago
>Applying an exterior coat does sound like an interesting idea. One concern I would have, is whether if and as it deteriorated, it might trap moisture and corrosives next to the tank, turning from protectant to trap and accelerant. This is a real concern, and one of the big problems with conformal coatings. The short of it is that when coating ferrous materials, you need to make sure as much rust as possible is removed before coating. (As rust forms, it takes up a greater volume that the iron is forms from. This results in pressure that will lift coatings, and allow water to seep underneath, accelerating wear.) Just to repeat, in your case, wire brush + the spray will probably net you another year or two, which is about what you could hope for with a tank that has already had seeping issues anyway. So I agree with your assessment of borrowing some rack time and giving it a shot. It is an inexpensive way to eek out a little more use of what you've got. >As for the alcohol blend fuels, I was aware that they help significantly in keeping the tank "dry". It's been my understanding that they may also contribute to the lower instances of "vapor lock" that we see, these days. At least, at my mild altitude and (mostly) non-extreme environment. Vapor lock used to be an issue when fuel pumps were located in the engine bay, powered off a rotating cam that ran a diaphragm pump from the gas tank to the carburetor. The pump would be pulling from the tank to the front of the car, then pushing from the pump a few feet up to the carb. Sometimes, in hot environments, the suction of the pump + heat of the engine bay would result in the fuel boiling inside the feed line before it reached the fuel pump itself, rendering it unable to pump any fuel at all until the system had cooled enough for the fuel to condense back to a liquid. Thus the term 'vapor lock'. Nowadays, everything uses fuel injection and high pressure lines, with the pump located in the gas tank itself. There isn't any low-pressure part of the system that would allow vapor lock to happen any more, so it ceased to be an issue. :)

Baeocystin 9y ago

>Applying an exterior coat does sound like an interesting idea. One concern I would have, is whether if and as it deteriorated, it might trap moisture and corrosives next to the tank, turning from protectant to trap and accelerant. This is a real concern, and one of the big problems with conformal coatings. The short of it is that when coating ferrous materials, you need to make sure as much rust as possible is removed before coating. (As rust forms, it takes up a greater volume that the iron is forms from. This results in pressure that will lift coatings, and allow water to seep underneath, accelerating wear.) Just to repeat, in your case, wire brush + the spray will probably net you another year or two, which is about what you could hope for with a tank that has already had seeping issues anyway. So I agree with your assessment of borrowing some rack time and giving it a shot. It is an inexpensive way to eek out a little more use of what you've got. >As for the alcohol blend fuels, I was aware that they help significantly in keeping the tank "dry". It's been my understanding that they may also contribute to the lower instances of "vapor lock" that we see, these days. At least, at my mild altitude and (mostly) non-extreme environment. Vapor lock used to be an issue when fuel pumps were located in the engine bay, powered off a rotating cam that ran a diaphragm pump from the gas tank to the carburetor. The pump would be pulling from the tank to the front of the car, then pushing from the pump a few feet up to the carb. Sometimes, in hot environments, the suction of the pump + heat of the engine bay would result in the fuel boiling inside the feed line before it reached the fuel pump itself, rendering it unable to pump any fuel at all until the system had cooled enough for the fuel to condense back to a liquid. Thus the term 'vapor lock'. Nowadays, everything uses fuel injection and high pressure lines, with the pump located in the gas tank itself. There isn't any low-pressure part of the system that would allow vapor lock to happen any more, so it ceased to be an issue. :)