Hey Guys,

The gas cap wont screw all the way down and seat. It starts clicking, and won't go any further. Its not going in far enough, and as the fuel tank pressure rises I can smell gas and hear to hissing out the filler tube. Finally took my car out on a spin long enough to notice this issue. I think I've had this problem for a long while, just didn't realize it.

Anyone run across this and figure out a solution? Its an aftermarket fuel tank that I wish I didn't have.

 

Yes , I did have this same problem . I noticed it when I was spilling gas on hard corners. I filed the grooves or threads on the cap with a triangular file and got it to fit better, but a new cap fix it completely. I test fit the new cap before I left the the parts store parking lot and was surprised at how much more smoothly it went on.

 

Thanks for the reply. I have 2 brand new caps. one that came with the tank, and a new AC Delco. both have the same issue. I'm afraid it is the filler neck that is causing the problem. But that is a good idea, I may have to do that with a new cap. BTW - what cap did you buy?

 

My Formula has done this since I've had it if I fill it up until it clicks off once. When I bought it, it had some kind of strange gold metal gas cap off another vehicle (no idea what it is) and I noticed the paint is pretty ruined under the gas door where gas has run down it constantly. Since, I have tried 5 different gas caps, none of which seal. I'm not sure if my tank is aftermarket or not, but the filler pipe bobs up and down like it's not attached, but is attached (which is strange). I could not find any breaks or cracks around the neck, it's like the whole section of tank is flexing when I move the filler neck up and down. I had planned on replacing the entire tank, but not until I find a good factory one or when the fuel pump goes out (whichever comes first). I am convinced all of the aftermarket tanks are pure garbage from what I read on here. I have tried filing the threads on caps too, but it still won't seal even though it physically goes on all of the way. I just gave up and only put 7 gallons at a time in it.

 

I can tell you its not normal, that is for sure! Thanks for the feedback. A rubber cork might do the job if the cap pushes against it correctly.

 

I've had this problem even with the new GM tank I installed back in 1989.

My experience, Stant caps seem to be the worst offenders. I had an emissions test station give me an odd, off brand cap that had a Dodge emblem looking twist grip on it because they couldn't get the existing cap to seal. It worked beautifully but it wouldn't let the door close all the way.

I think there's an old Fram cap on it now and it threads on without issue.

 

Thanks for feed back. I'm looking at rock auto cap choices, they all seem to be same diameter, but there are different depths. I wonder if the depth would make a difference?

 

just ran across this thread: https://www.thirdgen.org/forums/tech...ont-screw.html

https://www.ls1gto.com/threads/gas-c.../#post-5777823

 

The Early Metal One's Seem To Work Better.

.https://www.thirdgen.org/forums/hist...-cap-woes.html

 

It's been a couple years so I don't remember the brand but if you try it be for you leave it should go on very smoothly until it seats, when you get a good one you will know it.

 

Thanks for the link. Glad to know its not me, its the cap! Looks like filing is the key. Now that I've read other accounts, I'll bet it was working, but maybe the hotter day yesterday caused problems by expanding the plastic. didn't think I could go this long w/o noticing.

 

If only there was a way to seek out any previous threads with keywords like aftermarket tank and gas cap. Maybe someone has already done the leg work and figured out the replacement tanks use a later gas cap. Maybe they've even posted the part number of a cap that fits.

 

Thanks for the hint Drew, my search button is broken. Hoping to get that fixed as soon as I get this damn gas cap caper solved. You'd think, THINK, the cap that came with the tank would fit!

 

Try google. Comes up regularly. Someone made a phone call and found out a different cap fits. The aftermarket tanks take a 4th gen cap, iirc. I'd find the last thread, and post a link, but google is free for anyone. Just type what you're looking for, followed by site:thirdgen.org which will give forum results only.

 

It's fascinating how one engineer's poor, miscalculated decision leads to so many threads, posts, heartache, recalls and cars burning to the ground.

 

was kidding, thanks to your hint i found it. but results were all over the map once i looked at the specs. it’s still a trial and error game.

 

Here is the thread: https://www.thirdgen.org/forums/tech...termarket.html

And the gas caps mentioned that work: Stant 10826, crosses to a gates 31676 or Delco 12F52. If you look at the Rock Auto photos, they do indeed look like the same photo. But they list specs just a bit different.

And their specs:

Stant 10826 - post update ordered this, and it fits great.
https://www.rockauto.com/en/moreinfo...8598&jsn=10684
Neck Diameter (in) 1.750
Shell Diameter (in) 2.750
Cap Depth (in) 2.063


gates 31676
https://www.rockauto.com/en/moreinfo...73&jsn=3&jsn=3
Neck Diameter (in) 1.77
Shell Diameter (in) 2.78
Cap Depth (in) 2.05


Delco 12F52.
https://www.rockauto.com/en/moreinfo...46769&jsn=6773
Cap Depth (in) 2.1in

Stant 10834 (see post in this thread, Dorman Tank : https://www.thirdgen.org/forums/tech...ml#post6371789 )
https://www.rockauto.com/en/moreinfo...48604&jsn=6468
Neck Diameter (in) 1.750
Shell Diameter (in) 2.625
Depth (in) 1.750


ACDELCO GT174 - This one is giving me troubles
https://www.rockauto.com/en/moreinfo...51650&jsn=6797
Thread Diameter 1.831 in
Outside Diameter 2.78 IN
Depth 1.146 IN

Assuming Stant rounds, ACDelco doesn't care, and Gates gets it exact, the thread diameter difference is 1.831 - 1.77 = 0.061 in => 1.55 mm

 

I was looking at Mercedes cap seals last night and also discovered several other gas cap O rings. I wonder if a person could find the right size O ring that would sit flat in the neck allowing the cap to screw down tightly against it effectively preventing it from ever leaking again.

Also, I popped the factory metal gas cap off my 82 and it did indeed screw right onto my Formula neck perfectly. So, there might be something to that. I would have to fill the car up and drive it to see if it leaks though. Might try that this week.

 

That is how it should work. there is an o-ring at the base of the threads of the cap that should get snug against the end of the filler tube as the cap is screwed in tight. The base of the cap should bottom against the end of the filler tube and make a tight seal.

 

I don't know which aftermarket tank you are using, but I had this issue with a Dorman tank. I solved it as follows:

"Regarding the gas cap-- The factory cap definitely will not fit, but you don’t need to rethread the filler neck. I had a new OEM equivalent for an ‘85 Camaro, Stant 10822 and it wouldn’t go more than about one turn. I contacted the Dorman tech line by chat. They advised me that they used a Carquest / Stant 10834 cap for their testing. That cap fits a large number of newer GM and other vehicles. If you look up a 2010 Camaro V8, this should be the cap. It seems to seal well and no MIL lights. It would seem to me that if you have an emission test, the technician should use that 2010 Camaro application for his adapter."

Original thread posted:
https://www.thirdgen.org/forums/tech...fuel-tank.html

 

Thanks for the input. Just updated the list of caps above with the Stant 10834. Looks like the diameter is same as other that have been reported to work.

 

Based on the information that I received from Dorman, they ran validation testing to confirm that their product was safe and meets their design requirements. This cap (10834) was the one that they used to pass their tests for proper sealing.

 

Good info! When did you get/install your Dorman tank? Did it go in pretty easily and are you able to fill it up with gas with no problem? Or do you have to fill real slowly? Did the filler neck give you any troubles during installation?

 

Also would like to know this!

 

I bought this tank last fall (Sept 2019). After all the comments that I saw online about aftermarket tanks and fit problems, I was concerned, but it went rather well. The filler neck actually lined up better than the factory tank. My car is an '85 LB9 TPI, so it has the fuel injection tank. I wasn't especially happy about the shipping method, as the filler neck stuck out of the box. I needed to touch up the paint on the neck, but it was only scuffed, not deformed.
On installation, it appeared that the filler neck position was sensitive to how the "grooves" in the tank surface contacted the body rails. Those grooves or depressions in the tank stamping have the mounting tape in them. I tried to duplicate the thickness of the tape from the original tank with several layers of black PVC roofing sealing tape cut to width and the stack thickness checked with a dial caliper. That tape is stiffer than foam tape, yet still pliable. My plan was that if the filler neck was off, I would adjust the tape layers from corner to corner to try to shim and turn the tank a little. As it turned out, that wasn't necessary. The trick seemed to be to get the tank fully seated against the body rails. At first, the filler neck was off location as I started the bolts in the straps, but after I shook and twisted the tank a bit, it sort of popped into place and it was right on. I made sure the filler door pocket fit before I ran the straps all the way down.

I used a new Spectra sending unit and a Denso fuel pump with an AC Delco pulsator. The only issue there was that one of the terminals in the Spectra weatherpack harness connector to the car wasn't seated fully and backed out part way on installation causing intermittent low fuel pressure because the pump wasn't getting full voltage. Once I found that and pushed the terminal fully into the connector body until it latched, it was all good. It's worth checking all the details as it goes together.

I haven't yet filled it at the gas station pump as I have had the engine out and am just now getting it on the road. I have filled the tank with 5 gallon cans and it will take an upside down 5 gallon can (old vented cans - not EPA/CARB cans) as fast as it will flow without an issue. The only surprise is that it took over 5 gallons before the sender picked up from empty. At first, I thought that my sending unit wasn't working and I went back to recheck everything. On initial fill, I put about 20 gallons into the advertised ~15 gallon tank, so there must be several gallons in the bottom that can't be picked up. That's probably true of the factory tank, too, just interesting.

 

Thanks for all the details Dan! yes, the factory tanks act more or less this way. The first half of the tank takes a long time to burn off, and then the last half much quicker. (according to the fuel gauge that is)

Let us know how refuling at the gas pump works out. I may be in the market for a Dorman!

BTW - I bought the Stant 10826 and it fits great.

 

I did have an opportunity to fill it at a regular pump last week. About 3/4 of a tank and 11+ gallons. It seemed to work well and I didn't have any problems. The pump didn't seem to fill at a very fast rate, so I'll be watching for the next few fills and try a different station.

 

I'm glad I found this thread! I thought I was nuts, Filled up the other day and went for a ride, pulled the car into the garage in the house and I could smell gas after a while, looked for leaking fuel all over the place and finally traced it to the cap, pulled the T/A back out and put it into the outside garage, wife totally goes nuts if she smells gas lol. Gonna have to try a couple of these other caps because mine is definitely not sealing.

 

I bought a Stant #10822 for my GTA. According to their website, it's the exact fit. I got it and it spun into place perfectly, just like the original which I was replacing because the seal was bad.

The AC/Delco cap that I bought a couple of months ago just didn't fit well. The threads are not quite right.

 

What gas tank do you have? What was the model # on the AC Delco cap?

 

The tank is original.

This was the part that I got from Amazon, which claimed a fit for my GTA. I suppose maybe it fits because it didn't leak every time, but you have to be super careful when putting it on. Last time I filled up, I thought I was really careful and it still leaked. It never felt quite right. The new Stant screws on perfectly, just like the original.

 

I found a spare cap that I had laying around for my C4 and it fits really well, I drove it the other day and I didn't smell any gas but it was at a 1/4 tank and I was going to buy new lug nuts for my new rims for my truck and I wasn't even thinking about the gas cap lol, I wish I would have payed attention, oh well I'll know as soon as I fill up again.

 

I had this issue. Purchased a new cap. It fixed the problem. And a year later was doing the same thing. My father lightly sanded the cap threads with some sand paper. And it's been fine for years.

 

Update, The spare cap which I'm pretty sure was for my 93 C4 Corvette solved my problem, I've filled up a couple times and have had no gas smell or wetness around the filler neck

 

This is the most frustrating problem because you'd think it would be so easy to resolve.

Bought gas last night. I could tell right away that the Stant 10822 cap (OEM, according to Stant) that I bought in July wasn't going into the filler neck far enough. When I got home, once again I had to clean gas stains off the paint. The first couple of times I put this cap on, it easily spun into place. Last night I could not get it to set very deeply. How is that even possible? It was fitting so poorly that after it clicked, I could pull the cap off without turning it.

I took the advice here and sanded the threads down a bit. Now it seems to fit again. Just bizarre.

And I swear that I've never seen gasoline stain paint so easily. I've spilled some gas on other cars over the years and could just wipe it away. With my GTA, the stains have to be buffed out. Is it the old paint? The type of paint they used in 1988? Shell gasoline? Or am I imagining that it wasn't always this bad?