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Tii Fuel Tank Question


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My January 1973 tii has a beautifully painted fuel tank which is leaking fuel ever-so-slowly on my garage floor.  No, it's not leaking from the drain plug.  It almost looks like the tank is weeping fuel a few centimeters away from the plug.  I'm guessing my 40-year old tank has a pinhole leak...


I see that BMW sells only the later style tii tank.  Does it fit in the early (Roundie) cars without carving sheet metal?!  It looks like the later tanks use a different filler tube, but those are available, too.







January 30, 1973 Agave tii

April 24, 1974 Chamonix Turbo (German delivery)

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The later style tank will fit with no modifications to the sheet metal frame in the trunk floor.


If you don't want to use the later style rubber fill neck, I believe you can cut down the metal neck on the tank to accommodate your earlier style rubber fill neck.


You could also use a tank repair coating that will likely seal that little pinhole leak.  Mike Woolridge got an excellent result, although his use of the coating was to stop rust from forming inside the tank:   http://www.bmw2002faq.com/topic/147085-gas-tank-refurbishing/


Regards, Maurice.

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Mine did the same thing.  Hit it with a wire brush and you will see tons of little holes.  Rusts from the inside out, especially if the car sits.


You can also have it welded and sealed.  Keeps it original, and some shops provide a lifetime warranty.  Probably cheaper than a new tank.  Since the holes are already there, a simple reseal, even with the good stuff, will last maybe 3 to 5 years in my experience.


Good luck.

Edited by lilmo

1973 tii, agave, since 1992

1973 tii block 2763759

1967 Mustang GT fastback, since 1986

1999 Toyota 4Runner, 5 speed, ELocker, Supercharged

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Back in the early 80s something sharp on the Interstate got flipped up and made a small hole in my '73's gas tank.  Drained the tank, took it to a radiator shop and they soldered a penny over the hole--it's still there...no leaks either.  


Any good radiator shop can solder up a leaky tank, if it's not too much like Swiss cheese.  The shop should use CO2 or CO to fill the tank (vs water) after draining the gasoline.  Have 'em check the perimeter seam that joins top to bottom of the tank--that's a common place for 'em to rust and leak.  


When you drain the tank, run a ground wire from the car to the catch container if it's metal, or to the ground if you're draining into a plastic can.  Otherwise static electricity can build up from the flowing gas and cause an explosion.  I was in a dealership that was nearly destroyed by draining and un-grounded car, so be careful.


The advantage of repairing the old tank is the new ones don't have a drain plug.  




'69 Nevada sunroof-Wolfgang-bought new
'73 Sahara sunroof-Ludwig-since '78
'91 Brillantrot 318is sunroof-Georg Friederich 
Fiat Topolini (Benito & Luigi), Renault 4CVs (Anatole, Lucky Pierre, Brigette) & Kermit, the Bugeye Sprite

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If you don't want to use the later style rubber fill neck, I believe you can cut down the metal neck on the tank to accommodate your earlier style rubber fill neck.


If I remember right you can´t just use the newer rubber on an old-style car. The mount whelded in the side panel is different. At least it is for german cars. For a new tank in an old car you can just cut the metal neck of the tank, I agree on that. For an old tank in a new car you´ll have more problems.


Regards, Lars.

Ei guude wie? (Spoken as "I gooooda weee" and hessian idiom for "Hi, how are you?")


Já nevím, možná zítra.

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Very helpful, one and all!


I'm giving Permatex tanks sealer a try for a short term fix...when I used steel wool to clean off the area with a slow leak, it turned into a stream!  Wasn't prepared for that...  The hole was quite small, so I'm thinking the goo might not work.  If it falls off/starts leaking, I'll enlarge the hole a bit and give the goo another shot.  It's very strange working with an active gas leak, though!!


What I've learned about the new tank going in old car is that you need to change to the new style plastic fill tube, as you say...but I don't know if it is compatible with the fill location on the side of the car.  It also uses a different rubber gasket, which is still available.  We'll see.  I ordered a tank, and will report back to the forum!  It has to make its way to California from Deutschland. 

January 30, 1973 Agave tii

April 24, 1974 Chamonix Turbo (German delivery)

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Another fix:  get a "thick" piece of rubber.  Put a tiny hole through the center of the rubber.  Put a small sheet metal screw through the hole in the rubber.  Goop everything HEAVILY with Permatex.  Drive the screw into the hole nice & tight.  


It's beer time !!






p.s.  lengrep, keep us posted on the tank arrival.  If I'm in Simi when the work commences, I'll bring lots of beer, good cigars, and do what I do best:  stay out of the way and supervise.

Edited by OriginalOwner
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