I've got the gas tank blues.....

Not even a month after successfully replacing my gas tank that had a crack in the top of it......My replacement tank is now dripping when I fill it......
I have access to the module and lines and can see that it's nothing related to the module and it is not dripping from the fill vent hose channel.
This time, it appears to be leaking near the rear of the left rail channel (on top)
I'm beginning to think the left strap squeezes too tight?
I don't have any more tanks and this looks like a tough design to have duplicated in aluminum.
This sucks!

It is probably the vent line. Mine dripped from the vent hose itself. The reasoning is that it only leaks when you fill it. I had the same symptom, and it was the vent line. The line is 18mm. 3/4 inch will work, but you need to clamp it tight. You can not find the line during the weekends, so get it during the week, if you are going to work on it over the weekend. You need at least 8 inches, so you will be safe with a foot. You must drop the tank to access the inner clamp.

The tank should have a rubber rub strip across the top at the frame rails. The tank is flexible, and should not crack. It is difficult to put too much pressure on the tank with the strap, unless you used an impact wrench to install the bolts.

Where does it drip from? You can shoot smoke into the vent line, and see where it comes out.

The fill vent hose has it's own channel out the side that the hose sets in and that is not where the gas is dripping.....It is dripping from the rear of the left rail pocket when the car is parked facing uphill, so I'm expecting to find a crack near the rear in that pocket. I didn't find the crack in the other tank until I assembled it on the ground and pressurized it while sudsing it with bubbles....

If the gas is coming out of the top of the hose, it could migrate to the top of the tank. Obviously I can not see under the tank, but I have never had a crack in the tank. I have had two tanks that leaked, one the leak was never found, but you could smell the gas, the other dripped from the vent hose, not the tank. The first tank was smoke tested, but the smoke never showed up on the outside of the tank. Either way, the only time they leaked was when the tank was full. I guess you are going to be pulling the tank again. Dishwashing liquid, or kid's bubble liquid on the outside where the suspected leak is would give you bubbles at the leak when you pressurize the tank. You should have a piece of tubing handy just in case it is the vent hose.

Last month, post 9/23/16, I had two leaks on the top of my tank at the rear left and at the front right channels. Small hairline cracks found where the flat channel transitions up to the curve.   The one at the rear was more apparent and the front right showed up with smoke.  I found a replacement tank in Northern California with Buicknutt and installed it.  
The tank with the cracks was repaired using high density polyethylene welding rod sourced at “Grainger’s”.  No spark as an ignition source, however, as a precaution an argon purge was passed through the tank in a ventilated booth for the procedure at a temperature around 400 F.   It appears to have been successful, but not having been put into service, no way to be assured of the effectiveness.

I know where a couple of gas tanks are, the issue is shipping them to AZ from FL. If you can find someone who is disassembling cars instead of scrapping them, you may be able to find a tank locally.

It is nice to know a source for polyethylene welding rod. Let us know if you pressurize the tank, and check for leaks.

SF SoBay wrote:

Last month, post 9/23/16, I had two leaks on the top of my tank at the rear left and at the front right channels. Small hairline cracks found where the flat channel transitions up to the curve.   The one at the rear was more apparent and the front right showed up with smoke.  I found a replacement tank in Northern California with Buicknutt and installed it.  
The tank with the cracks was repaired using high density polyethylene welding rod sourced at “Grainger’s”.  No spark as an ignition source, however, as a precaution an argon purge was passed through the tank in a ventilated booth for the procedure at a temperature around 400 F.   It appears to have been successful, but not having been put into service, no way to be assured of the effectiveness.

Hmmm......Polyethylene welding is something auto body shops would specialize in, right?......A hillbilly alternative to your argom purge is to pump exhaust gas into the tank while welding OR..... I saw a guy on youtube light a fire over the fill opening on motorcycle tanks before welding-- I'll be the guy watching from a safe distance while holding his beer!....... The crack in my previous tank is as you described on the right front of yours.....I never would have found the leak without soaping it while under pressure because it really wasn't an open wound. Even today, with the surface clean, you would not suspect a leak in that location by simply examining it..... It obviously is an area that has complex shape transitions over an area that isn't big enough to absorb any flexing..... In this desert environment, plastics dry out and get brittle and I'm sure the fumes from ethanol-laced gas doesn't help to preserve it...... Trouble with used tanks is that they are also over 20 years old..... It amazes me that popular GM wagons made for 7 years don't warrant the mfg of replacement tanks..... The complex shape requirement of the top of the tank mostly prevents a custom aluminum tank from being practical

AzDon, I tried to no avail to post pictures of the tank and the welding process.  I am adept at navigating into cul de sacs with a computer.  Five attempts and I remain unenlightened.  My son will be here on Thursday and images could possibly appear.
I understand your frustration; I was able to locate a tank a couple hours drive away.  There was a tank in Southern California, but they don’t ship??

With the assistance from my son, here are some pics:


Leak at rear left of tank.


Heat welding


Garage floor decoration.


Leak at front right of tank.


Leak at rear left of tank.

The rust mark on the tank next to the fracture might have contributed from pressure exerted on the channel of the tank.

AzDon,

You might want to consider looking in your area for a training facility to perform the welding.  There could even be a school for welding who would welcome he project.  Other possibilities are an occupational training center, trade school or a trades union training facility.

Grainger’s part number for the welding rod is “4UZV9” HDPE 5/32 black.  That’s enough rod to repair 200 tanks; you could become the wizard of leaky tanks.

Good luck,

Bill

I think nobody is doing this work professionally because....
The tanks say right on them "Unrepairable" and research on the internet is unencouraging (example: file:///C:/Documents%20and%20Settings/User/My%20Documents/Downloads/Repairing-Polyethylene%20(2).pdf ).....The liability of a failed gas tank repair might be too much risk!
There would be a learning curve that would probably produce more failure than success.....
Thanks for posting pics of the top of the tank showing the rail pockets and the much deeper channel that the fill vent hose occupies..... Because the hose fits loosely in that slot, I'd expect a leak in that hose to run out the side around the hose itself.......

I must say i,m pretty impressed with all this technical stuff when fixing a gas tank crack,.

The argon purge certainly sounds pretty cool,. and i like the heat gun looking thing that welds and enters new plastic as it does it,..

All way above my pay grade and budget allocated to fix a gas tank crack,.

I probably did it all wrong,. but,. the blue wagon had a leak, so i dropped the the tank onto a jack (still had gas in it),. and took my little dremel, and ground open ( 'Veed" it basically) the crack (on the top corner of the tank,) and then used JB plastic weld,.and my trusty finger to squish the JB into the crack that was now a lot wider etc,.
I must confess, i didn't really research the label,. or what the gas tank is made of. The members here are much more technical (smarter?) than me,. to me its a plastic tank end of story,.JB plastic weld to fix plastic right?
So that was 7-8 years ago,. and the tank hasn't leaked yet,.but the jb weld is a different color than the tank,. so i maybe should have gotten the proper shade and kind of paint to hide the repair better,.
but i can't see it from the drivers seat when i,m driving so it doesn't bother me,.
In fact i'd forgotten about it untill i read all about the troubles here with the hot climates and their effect on the tanks,.
I will say i didn't overtighten the gas tank straps, because i notice the tank starts to deform if you do,. but a lot of folks are worried the tank will fall out so they make sure its in there solidly,.
Up here in the eastern climates of the rust belt, we are lucky enough to get experience with all kinds of alternate ways to hold a gas tank onto the body,. i.e bungy cords, wire coat hangers etc,.which lets you comprehend just how very little it takes to hold the tank up there sometimes,.

JB Weld, I like it, in spite of the color faux pas.

""Is there anything that J-B Weld WON’T bond to?

J-B Weld will not adhere or bond well to: ◦Any flexible rubber surface
◦Leather
◦Vinyl
◦Canvas
◦Polypropylene plastic
◦Polyethylene plastic""

Rev Bob wrote:

J-B Weld will not adhere or bond well to: ◦Any flexible rubber surface
◦Polypropylene plastic
◦Polyethylene plastic""

I did use JB PLASTIC weld,. i think its different compound than regular jb epoxy,.

It's probably a good thing its being used more as a splash barrier than an stressed part,.

""I did use JB PLASTIC weld,.""

Got it. Thanks. I missed the "plastic" part in your post.