Fuel Tank Damage - Help with cause?

[Count_Fred]

About a year ago, my fuel tank started leaking. I dropped it and discovered a crack at one of the bends in the tank. I replaced it with another used tank. Less than a year later it has developed a crack in the same spot.

Any idea as to what is happening?

My charcoal canister has been misbehaving and pressuring the tank more than it should. I have a hard time believing this is causing enough pressure to push the tank out enough to cause it to rub and eventually crack.

I'm going to get the original tank welded to fix it before putting it back in. I don't want yet another used tank until I understand why it's failing. There is some sign of rubbing on the body, but no burrs or other protrusions.

I'm at a loss as to cause. I've heard of people really landing on their tank to no ill effect, and I don't recall a particular landing that might have cause either failure on mine. The last drive before the current one died was all freeway driving.

The tank. The crack area was stripped clean when I tried to seal it

Close up of the crack

Looking up at the body with rub marks.

Cheers,
JFS III

 

[Rice]

You will want to get in touch with JFZ80. He is still trying to chase down the cause. Perhaps you two can compare notes and discover a common denominator. He is somewhere between repair number 6 or 8 with cracks in what appears to be the same spot as yours.

 

[jfz80]

Read up here and post your analysis or conclusions there or link your thread to aid future searchers

Schlacker said he had the same failure before but sold the vehicle i believe--didnt have a fix for it
PPC had the issue as well but was subdued with a new junkyard tank i think
My solution has been half tank at a time and dont park downhill but its past time to get onto the proper fix. Read through the thread for and see if there is a fix for you and if not join in. I imagine we will drag out at least one more leaking lurker

Have not figured out the cause but those body scrub marks seem like an obvious place to start.
EDIT... looking closer it looks like that rub mark is on the opposite side of ebrake channel from crack but that corner of tank doesnt look bad.
That and the Charcoal canister you mentioned. Have you checked where the vent for the CC terminates inside the front drives side frame rail? it can become plugged with mud rust instect etc and prevent venting.

I added new used CC and new gas cap just to ensure proper function with no luck. I have not plumbed a vaccum/pressure gauge in cab to watch as recommended to me on that thread yet.

Maybe paint the tank with rtv or something like it and install and see if it makes contact after a tankful.
My body bracing there was super clean with no marks but now yours makes me want to inspect that spot again. Though I tried the double and triple pads to space the tank down a hair. May want to inspect your body mounts to see if you have extra body flex, though mine were tight. or at least put a patch over that spot and see if it gets worn


Ive tried welding a couple times and brazing once with no luck as well as a couple tank repair kits. JB weld has actually held the longest. "new" used tanks last 4-6 months maybe so i believe its determining if the failure is from physical stress of bending/twisting etc or pressure. I had believed it was due to pressure but your body scub marks look suspicious to me. Mine originally occurred in DD use when i got a full tank and noticed the leak at home.

 

[thedoughboy]

My brother-in-laws '94 had a similar thing happen. Repaired several times. Ended up having to put a new tank in there.