neilh

I dropped the gas tank strap to replace a leaking hose line, and now find i also have a bigger problem!

Has anyone successfully repaired a hair line crack in the fuel tank? The crack is on the right underside forward edge ( looking from the back) where the strap rubs on the tank, looks like it has been rubbing forever, the strips installed to stop strap to tank contact are misaligned.

Any ideas? Anyone have a 81 fuel tank they don't need :-)

Neil

Jim bailey - 928 International

We have an "extra" fuel tank $450 with one year warranty.

neilh

Jim, i'll be calling shortly.
Thanks
Neil

jpitman2

As said elswhere, it seems that repairs can fail due to allowing fix to cure unloaded, then it breaks when you replace tank in car and tighten straps. A friend has successfully refitted a spun threaded insert with epoxy, no leaks.
jp 83 Euro S AT 50k

neilh

thanks, jp.
Yes, i've read all the past threads, and i'm going replacement route.


Cheers,

Neil

928ntslow

I've made 3 welds to a tank and thought I fixed it each time...thats my answer. My next shot is a slurry mixture to coat the inside. This is the last resort.

neilh

Tank is out. What a PITA, the shop manuals don't show the breather that goes from the top of the tank, through the chassis side rail to the top breather connection at the filler, hung up on it for some time before i realized, quick cut, tank dropped!
My tank is leaking right on the perimeter of the fuel well, right at the lowest point of the tank. its a hair line crack, if i apply pressure, i see a tell tale line of gas.
Replacement, here i come.....

mark kibort

its thermo plastic and you can use a 100watt soldering iron and do a gross weld. then, cover it with JBweld, and you are done.

mk

928ntslow

Mark, you say this as if you have successfully made repairs to a tank. Did you and was it permanent? What type of leak was it?

mark kibort

it was a cut made when i was cutting things out of the chassis with a sawsall.

the JBweld makes i perminant, and it works unbelievably well. especially on a crack, as it fills it in and actually bonds with the thermoplastic the tanks are made from. i did a recent repair on that expansion tank above the rear wheel , made from the same materials.. when it dried, it was hard as rock and even the epoxy on the edges couldnt be pealed up with a knife.

mk

Jim bailey - 928 International

When the fuel tanks crack and leak on the bottom it is the result of the fatigue cause by the flexing of the plastic from 10-20 gallons of fuel (60 to 120 lbs ) sloshing about inside the tank for 15 - 20 years. No amount of J B weld is going to restore the integrity of the tank it might stop leaking for a little while but it is not really fixed. Holes on the top of the tank like screws drilled in to mount stereo equipment on the rear deck probably could be plastic welded and covered with J B weld since they are under little or no stress.

mark kibort

good point Jim. mine didnt leak, but maybe enough time hadnt gone buy.

Duhh, why else would there be a crack. stress!!! 150lbs hanging by the strap

MK

neilh

Yup, what Jim Said!

I worked for Alfa Romeo many years ago as a design intern doing my Mech Eng degree, and they taught me that there are two things you don't do, 1) bolt aluminum body panels up tight to steel parts ( 'cause the expansion rates are different!) , and 2) ditto for plastic. Thats why our tanks hang in a sloppy strap.

Bonding JB to plastic will only work if the plastic can't move, stress or change its profile for any reason. 100# to 150# of gas in a tank changes the shape of the tank, and the JB wili separate from the plastic eventually.

Jims getting my call for the replacement tank..
Neil

928ntslow

I still don't know why plastic welding didn't work. The only reason I can guess, is because the heat changes the molecular structure of the plastic and does not reatin the same flexibility after. I thought for sure I did a fine welding job and blended the old and new plastic compounds. Kinda pisses me really.
I am still going to try to fix my leaky tank somehow. There has got to be a way.

dr bob

Like welding metal, it's a duel between getting full penetration in your welds and avoiding getting the plastic too hot. There's also the issue of cleanliness; The reason you are fixing a crack is because it's leaking, and that means that fuel and all the garbage that comes with it has been weeping through and evaporating. All the 'low boilers' flash off and leave the rest as sludge or varnish inside the crack. It may seem counterintuitive, but a "good" plastic repair often includes removing the damaged/comtaminated sections completely, then using a plastic filler to take care of the gap. Drill out the ends of the cracks' similar to the way good fiberglass crack repaisr are done, so that the end of the crack repair isn't a new crack waiting to happen.

The tanks are HDPE, in a 'high molecular weight' version to make the gasoline stay inside. Mark Anderson once posted the name of the resin used, and it wasn't one that I recognized instantly. You'ld need to know that info to get the right filler material.