Gas Tank Leak at Filler Neck - Help

[mirose]

So today was the big day. I got my plates and took the car for its first legal drive (I know, pictures are needed..but that will be another post...this one is to figure out what the hell is going on with my gas tank).

Anyway, my first order of business was to get gas. The tank was just about full when the attendant (you have to have full serve in NJ...its a law) told me that gas was leaking pretty badly in the back....

So I got under the car and sure enough right where the metal filler neck enters the gas tank it was leaking like a sieve. About a gallon leaked out until I guess the level went below the filler neck, and then it stopped.

Anyone have this problem? I don't seem to have any torque or pressure on the metal filler neck that is deforming the gasket...its quite loose actually. Maybe looser than it should be.

And for the record, its a complete kit and I used all the parts that came with the kit...no donor tank or anything like that.

thanks,

Michael

[Rich A]

The seal isn't installed correctly or you need a new seal.

[PhoneGuy]

Originally Posted by Rich A

The seal isn't installed correctly or you need a new seal.

So how can you tell if it is installed incorrectly or that you need a new seal without a leak test?

[CCRsAC]

Did you lubricate the seal and/or filler pipe before assembly? Not sure it's necessary or would help with ensuring a good seal, but I gave both a good coating of engine oil before inserting the tube through the seal.

[Dan Babb]

Is the filler neck going in the tank pretty straight or at an angle? If it's at an angle, that could effect how the rubber seals around the neck.

[bfitz241]

I had this same problem with the FFR filler neck. Threw it out, bought a used Mustang filler, cut and welded it to shape. No more leaks.
Before that I had tried 2 new Ford seals for the tank.
Good luck.

[2yrproject]

Check out this thread:

Fuel filler pipe at tank leaking?

I followed the instructions on post #10 with the 10-40 oil and no leak.

Different story on the fuel sender gasket, that was leaking and I just replaced it.

Good luck and congrats on getting your car on the road.

[SJDave]

After sitting for several years with the filler neck cable tied to the frame and putting side pressure on the gasket, mine leaked at the first fillup also. The Gasket actually had a slight tear in it from the pressure not being even all that time. I replaced the gasket, lubed like everyone is saying and it just has the smallest drool through the grease when full. Looks like another marginal design element, maybe some pipes are better then others, but the whole setup appears half ass. ** I would recommend always replacing the gasket when you go to put the body on.

My sender unit leaked too, it's really hard to keep that "square" cross section O-ring sitting flat when you tighten the wedge ring. Mine was twisted when I removed it. Put a new gasket in, lots of grease on it, got it not to twist this time and it seals fine. You can really appreciate how "cheap" these parts are and how unforgiving they are to installation by anyone who hasn't done it 5 times before.

[2yrproject]

Yea, the best part about the replacement fuel sender gasket is the price. It was $1.12 out the door at the Ford dealer. Part No. COAF9276A in case anyone needs it.

[emac]

I think you have about the same era mkiv as me. I recall the filler neck hit the frame when the tank went in. Do you think that whatever you did to make it clear the frame could be causing the leak. Just a thought. I really don't see how the thing doesn't leak, considering the design!

Ernest

[mirose]

Originally Posted by SJDave

After sitting for several years with the filler neck cable tied to the frame and putting side pressure on the gasket, mine leaked at the first fillup also. The Gasket actually had a slight tear in it from the pressure not being even all that time. I replaced the gasket, lubed like everyone is saying and it just has the smallest drool through the grease when full. Looks like another marginal design element, maybe some pipes are better then others, but the whole setup appears half ass. ** I would recommend always replacing the gasket when you go to put the body on.

I bet this is the whole deal right here...I presume its a pretty easy swap out....I might as well just get a new gasket.

Originally Posted by emac

I think you have about the same era mkiv as me. I recall the filler neck hit the frame when the tank went in. Do you think that whatever you did to make it clear the frame could be causing the leak. Just a thought. I really don't see how the thing doesn't leak, considering the design!

Ernest

Ernest, your memory might be better than mine but I don't recall having to bend anything. I bet Dave is onto something that the thing sat there with the filler neck unsupported and was mushing against the gasket and it probably deforms it...plus, it probably gets a little stiff and dry because there was no gas in the tank for a long time..and also I probably was very skimpy with any lube...I probably was worried about getting any impurities into the gas tank.

I am going to presume that its just easier to replace the gasket and move on. I just hope its something relatively simple. I can't imagine its too hard. Plus, I have a few other gremlins to work out in my car and its looking like I will have to take off the body anyway...that will make this pretty simple.

thanks

Michael

[mirose]

Anyone know what year gas tank comes with the complete kit? I need to order this gasket....They all look the same but they seem to go by groups of years.

thanks

-Michael

[rich grsc]

Its a Dorman, #577-502

[mirose]

Originally Posted by rich grsc

Its a Dorman, #577-502

Thanks. I ordered it from amazon....I love that site.

-M

[Purple Venom]

Timely post as I've been having the same issue lately.

[KRUSTY990]

I too was prepared to lube the filler neck gasket when I came upon a Ford service bulletin saying "do not use any lubricant on gasket". Kinda went against common logic but I went with it. 4 years later and not a drop. WTH???

krusty

[Fred Yarema]

a guy stopped me on Saturday to tell me I was leaking fuel - had just filled it up. The old grommet (FFR supplied) tore apart when I pulled it out - crappy rubber - must have had a crack in it. The new one on the left is frem NAPA - better molded - looks like better rubber as well. Wasn't cheap - $28.00. Doesn't leak a drop now - not even a wiff of fuel back there. I did lube it with some motor oil for installation.

[mirose]

Originally Posted by Fred Yarema

a guy stopped me on Saturday to tell me I was leaking fuel - had just filled it up. The old grommet (FFR supplied) tore apart when I pulled it out - crappy rubber - must have had a crack in it. The new one on the left is frem NAPA - better molded - looks like better rubber as well. Wasn't cheap - $28.00. Doesn't leak a drop now - not even a wiff of fuel back there. I did lube it with some motor oil for installation.

Thanks. I already ordered one from Dorman....Hopefully it will be better than the one that came with the kit. If not I'll go with the NAPA one. Mine was 23 bucks but free delivery.

It seems this is a big problem with these tanks. If you google the part number, it takes you to all kinds of threads on mustang forums of people with the exact same issue.

Hopefully this will be non-issue in a few days when my part comes.

-Michael

[Rich A]

Originally Posted by Rich A

The seal isn't installed correctly or you need a new seal.

Too simple.

[rich grsc]

Do you have the metal bracket that holds the steel fill tube in place? That would keep it in alignment.

[mirose]

Originally Posted by Rich A

Too simple.

I guess it could be something bigger than this, but look at the other people already that have chimed in saying they have the same problem? And what about all of the other mustang forums I discovered that say exactly the same thing? Its a metal neck going through a rubber gasket into a metal gas tank. The rubber gets deformed and the fuel leaks. It makes sense to me and I can't really come up with anything else...I saw the leak, I saw where it was coming from and there isn't any other seal or seam up there other than this gasket.

Originally Posted by rich grsc

Do you have the metal bracket that holds the steel fill tube in place? That would keep it in alignment.

Yes. Actually, that doesn't keep it in alignment as much as it just holds it from being pulled out as there is a flange on the metal neck that is larger than the diameter of the bracket. Yes, it may help keep the alignment to some degree but it isn't nearly as sturdy as it probably could have been.

[Fred Yarema]

Quote:
Originally Posted by Rich A
The seal isn't installed correctly or you need a new seal.

Too simple.

We're pointing out that threre is an obvious problem with the FFR seal - poor quality - get one elsewhere to save installing it twice. A smug "too simple" doesn't help much Rich!

[Rich A]

Originally Posted by Fred Yarema

We're pointing out that threre is an obvious problem with the FFR seal - poor quality - get one elsewhere to save installing it twice.

And Fred what did I say in the first post! It isn't the tank or the filler neck leaking, SO it must be the seal.

[mirose]

So this is the gasket I pulled out today....



I put the new one in, but don't have time to go fill up to be sure its sealing. In addition to the 18 mos sitting in the garage with the filler neck torquing the seal, I think this design flaw is part of the issue...Note how the metal fuel filler neck is in contact with the 3/4 inch tube...either the fuel neck really should be modified (read: Bent) in that area or the 3/4 inch tube should be ground down. When you tighten the tank straps it pushes down on the filler neck and that deforms the gasket. I had to drop the tank 1 inch to get the retainer clip thingy out from under that 3/4 inch tube...when I tightened it back up I didn't make it quite so tight as last time. The tube is certainly pushed down a tiny bit, but not as much as before. If it happens again I will modify the filler neck.

[Joe]

I know it probably doesn't help much, but my MK3 has more than 1/2" clearance in that area..

[Joe]

Just to confirm, does your tank mount on the passenger/filler side of the tank look similar to this? You don't by chance lack the bolt spacer and have the tank sliding up the side of the vertical frame member, rather than flush with the tank flange do you?

[mirose]

Originally Posted by Joe

I know it probably doesn't help much, but my MK3 has more than 1/2" clearance in that area..

They changed the rear end so much between MK3 and MKIV...so I don't know how much stock to put into this difference.

Originally Posted by Joe

Just to confirm, does your tank mount on the passenger/filler side of the tank look similar to this?

Yes, it looks very much like that. Actually, but if you look closely, your tank isn't even contacting the contact point that the tank is supposed to press up against. so I think either I am wrong to have mine so tight, or you are wrong to have yours so loose. And I don't have a spacer...I just tightened the strap until It was snug...but its a similar amount of exposed bolt to what your spacer is. I'll get in there and take a pic tomorrow.

Maybe someone else with an MKIV and a complete kit can look at their tank and see if they have similar clearance issues that I have.

-Michael

[Joe]

Originally Posted by mirose

They changed the rear end so much between MK3 and MKIV...so I don't know how stock to put into this difference.




Yes, it looks very much like that.

Maybe someone else with an MKIV and a complete kit can look at their tank and see if they have similar clearance issues that I have.

-Michael

yo-k.. good luck.. maybe things changed with the MK4..

[rich grsc]

Originally Posted by emac

I think you have about the same era mkiv as me. I recall the filler neck hit the frame when the tank went in. Do you think that whatever you did to make it clear the frame could be causing the leak. Just a thought. I really don't see how the thing doesn't leak, considering the design!

Ernest

This says it all. The fill tube should NOT hit the frame. You can bend the frame up with a BFH, or dimple the fill tube with same BFH (my preference), or a third option, put spacers on the tank legs to lower the tank about 1/2".
They changed the rear end so much between MK3 and MKIV...so I don't know how much stock to put into this difference., this is true.

[mirose]

Originally Posted by rich grsc

This says it all. The fill tube should NOT hit the frame. You can bend the frame up with a BFH, or dimple the fill tube with same BFH (my preference), or a third option, put spacers on the tank legs to lower the tank about 1/2".

I'd go with BFH to the fill tube too. And that will be my plan.

Thanks.