New gas tank not air tight?

[70pumpkin]

A new gas tank (tanks inc from Summit or Jegs) was installed a while back.  I never entirely fill it up, but yesterday I did.  Now there's a strong gasoline smell in the garage -- this never happened in the past.  Are these new tanks just not as air tight as the originals?

[MoparLeo]

Get it up on a rack and check it. There are vent hoses at the top depending on year and they may be bad.

[JH27N0B]

Is your car a '70? These tanks vent through a line into one of the rear frame rails (except on California N95 cars) in 1970. If you fill up the tank, then park the car in the garage, and it warms up, the gas expands, and can get into the vent tube in the filler neck, travel through the line, and into the frame rail.
I've had trouble with a gas tank I installed on my 71 Challenger where the filler neck installs into the tank.  If I fill the tank to full, it will sometimes seep around the grommet and drip on the floor.  I don't know what went wrong there, I don't think I did anything wrong installing the grommet, I think the quality of parts often isn't that great these days and the grommet just didn't seal as well as it should.
Also, gas can leak from where the sender unit is installed if the seal isn't good there.

[Dakota]

is this tank on a Challenger or a Cuda?   If you have a filler neck behind the license plate and filled the tank when it was cool, there might've been enough thermal expansion later in the day to push some gas towards or out the filler tube. 

Depending on how your car is equipped, the vent line from the gas tank would be terminated in the passenger side rear wheel well or routed up front to the engine compartment to be fed into the engine or possibly sent to carbon canister before being routed to the engine.   My car is a '70 Challenger so that's really the only one I can describe with some level of certainty.  As suggested above, you'll want to look at the vent line connection to the tank and follow the line wherever it goes from there.

Other possible sources:

Over the years on this forum and elsewhere, I've seen lots of posts about how newer lock rings and gaskets for the level sending unit are not sealing well where the exit the tank, so that's a place to check.

Lastly, the first time I put the filler tube into my new gas tank, I managed to tear the grommet where it necks down to match the size of the hole in the tank.   It was not evident until after I filled the tank past 3/4 full.   The gas was coming out fast and furious from this leak.   Loved making that phone call to my wife to ask her to bring me a gas can and the manual fuel pump so I could partially empty the tank to stop the leak (it happened in front of a store I stopped at to sneak a snack).

 

[7212Mopar]

Jeff. Check the grommet at the tank for the filler tube. It is easily damaged during install. I needed a second one when I did mine. Also it can leak where the sending unit is mounted. The replacement locking ring is lighter gauge than stock. I reinstalled my stock locking ring and the problem was fixed.

[70Challenger440]

I too had the issue with the fuel sending unit. It never sealed well. I smeared some gas resistant Seal-All 380112 around the edge of it.. Smell and minor  leak went away, and never returned.

[70pumpkin]

Went under the car yesterday.  Looks like there's a leak at the top right corner where the seams come together.  I'm not sure what the warranty is for tanksinc but will place a call today. 

Drove the car for a long time to burn gas -- must have burned enough so that the gas is below the leak cuz the smell and leak are now gone.

Is there a sealer that can be used around the seam edges? 

[7212Mopar]

That looks like the passenger side. Are you sure is not from the filler neck grommet that get on the tank seam?

[70pumpkin]

Yes, it's on the passenger side but it looked like the leak was coming from the corner itself, not dripping from above. 
Spoke to Tanks and their standard warranty is 3y from date of purchase.  Mine is just a bit older :-( but the manager over there (Justin) said he could provide a new one at 60% off!  He didn't think the leak was from the seam itself as all their tanks are pressure tested.
I need to diagnose it a bit more.

[chargerdon]

When i put in my new tank i also got a leak at the grommet for the filler tube.   Took it out and the grommet looked fine, but, took the tube back out and spent the time to sand down the filler tube where it enters the tank and reinstalled.   That helped but the next time i filled the tank it still leaked just not as bad.   Tried a second grommet and it still leaked.   (note, i would always finish filling the tank with a gas can at my home). 

Finally, i did something that is not recommended!!!   Before inserting the tube i filled the grove in the grommet with black gasket seal, and then inserted the grommet, and then after putting in the tube, worked on putting more black sealant on the tube itself.   I let it dry for two days before putting in the gas, and its been fine now for 4 years.   

[7212Mopar]

The two halves of the tank is continuously welded at the flanges, not at the seams. May be smear some gasoline rated sealant at the suspected seam area to see if that makes a difference. If no change, try sealant between gasket and filler tube around from the outside. I would try that before spending time to take the tank down.

[70pumpkin]

Thanks for the tip Warren.  Tank is no longer full so there's no smell or leaking rn.  Next time I fill up, I'll take a much closer look.