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Best Way To Seal Fuel Tank Opening

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Gary Lewis

Best Way To Seal Fuel Tank Opening

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I'm having to replace the o-ring on the midship tank on Big Blue as it leaks. Again. I replaced it about 2 years ago, but apparently didn't do a perfect job, so now I'm wondering what is the best way to seal the o-ring? And the o-ring is the one under the lock ring, as shown below.

So is there a sealant, like maybe Permatex Permashield, that will hold the o-ring in place for assembly awa seal it? I'd rather not do this again.

Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

Rusty_S85

Re: Best Way To Seal Fuel Tank Opening

Gary Lewis wrote

I'm having to replace the o-ring on the midship tank on Big Blue as it leaks. Again. I replaced it about 2 years ago, but apparently didn't do a perfect job, so now I'm wondering what is the best way to seal the o-ring? And the o-ring is the one under the lock ring, as shown below.

So is there a sealant, like maybe Permatex Permashield, that will hold the o-ring in place for assembly awa seal it? I'd rather not do this again.

How tight does the ring fit? Ive had to take a hammer and a screw driver to the tank and ding the ears down to hold the plate tighter before. If the fit is good and the O ring is simply popping out of the groove, you could try some fuel safe gasket adhesive to stick the O ring into the groove and keep it form possibly moving.

"Old Blue" - '56 Fairlane Town Sedan - 292-4V, Ford-O-Matic transmission, 3.22:1
'63 Belair 2dr sdn - 283-4V, Powerglide transmission, 4.56:1
'78 Cougar XR7 - 351-2V, FMX transmission, 2.75:1 9inch
"Bruno" - '82 F150 Flareside - 302-2V, C6 transmission, 2.75:1 9inch, 31x10.50-15 BFG KO2

Gary Lewis

Re: Best Way To Seal Fuel Tank Opening

Administrator

The existing ring fit tightly when I put it on, although I haven't tested it lately. But I'd bet it is still quite tight.

But we are thinking alike - the o-ring may be popping out of the groove. And that Permatex is "fuel resistant" so should work.

However, it is also sticky and I'm wondering if it might cause the o-ring to try to follow the lock ring on the top side and be stuck on the bottom if I put it all over the o-ring. So maybe goo the tank and lay the o-ring in it then oil the lock ring and put it on?

Or, I've thought about using Loctite PTFE goo instead of the Permatex. The writeup on it says "Loctite 567 seals threaded pipe and fittings instantly, then slowly hard-cures to form an insoluble seal which exceeds the pressure rating of all sized pipes. Lubricates threads during assembly and permits accurate positioning of elbow, valve and gauges before setting. Excellent chemical resistance. Temp. range: -65F to 400F (-54C to 204C)."

Gary, AKA "Gary fellow": Profile

grumpin

Re: Best Way To Seal Fuel Tank Opening

I used Dow Corning 4 on o rings on aircraft. A dielectric compound. That stuff is kind of spendy.

Silicone is good to use, keeps the o ring in place to do it’s job.

Dane
1986 F250HD SC XLT Lariat 4x4 460 C6-Sold
1992 Bronco XLT 4x4 351W E4OD
1998 GMC Sierra SLE K1500 350 4L60E
Arizona

Gary Lewis

Re: Best Way To Seal Fuel Tank Opening

Administrator

Dane - I just happen to have Dow Corning 4, which I use to fill cable connectors before inserting the wire and crimping them to make sure nothing else gets in.

So you are saying to coat the o-ring w/it and lay it on the tank, put the clamp ring on it, and tighten it up? Nothing more?

It is sticky enough that the o-ring won't jump out of the depression it fits in and yet it is slick enough to let the lock ring slide?

How 'bout a deviation: I coat the tank's groove with the Permatex and lay the ring in it and let that set up a bit. Then coat the clamp ring with the silicon and put it in place. Might that give me a better chance for the o-ring to stay put?

Gary, AKA "Gary fellow": Profile

Rusty_S85

Re: Best Way To Seal Fuel Tank Opening

In reply to this post by Gary Lewis

Gary Lewis wrote

The existing ring fit tightly when I put it on, although I haven't tested it lately. But I'd bet it is still quite tight.

But we are thinking alike - the o-ring may be popping out of the groove. And that Permatex is "fuel resistant" so should work.

However, it is also sticky and I'm wondering if it might cause the o-ring to try to follow the lock ring on the top side and be stuck on the bottom if I put it all over the o-ring. So maybe goo the tank and lay the o-ring in it then oil the lock ring and put it on?

Or, I've thought about using Loctite PTFE goo instead of the Permatex. The writeup on it says "Loctite 567 seals threaded pipe and fittings instantly, then slowly hard-cures to form an insoluble seal which exceeds the pressure rating of all sized pipes. Lubricates threads during assembly and permits accurate positioning of elbow, valve and gauges before setting. Excellent chemical resistance. Temp. range: -65F to 400F (-54C to 204C)."

I would only apply it to the tank side and just enough to lock the o ring in place. Dont put too much as it will make life hard if you ever have to clean the groove out down the road. This should prevent it from trying to stick to the lock ring as well.

Gary Lewis

Re: Best Way To Seal Fuel Tank Opening

Administrator

Rusty_S85 wrote

I would only apply it to the tank side and just enough to lock the o ring in place. Dont put too much as it will make life hard if you ever have to clean the groove out down the road. This should prevent it from trying to stick to the lock ring as well.

Which "it"? Permatex or the PTFE? Permatex has to be cleaned out with brake cleaner, but the PTFE will wipe out fairly well.

Gary, AKA "Gary fellow": Profile

grumpin

Re: Best Way To Seal Fuel Tank Opening

In reply to this post by Gary Lewis

Gary Lewis wrote

Dane - I just happen to have Dow Corning 4, which I use to fill cable connectors before inserting the wire and crimping them to make sure nothing else gets in.

So you are saying to coat the o-ring w/it and lay it on the tank, put the clamp ring on it, and tighten it up? Nothing more?

It is sticky enough that the o-ring won't jump out of the depression it fits in and yet it is slick enough to let the lock ring slide?

That’s what I would do. If it doesn’t work try your deviation method.

Here’s a picture of Pratt and Whitney PT6 turbine nozzles. 4 o rings per nozzle, 14 nozzles. I used to squirt a dollop of DC4 in my hand add the o rings and rub my hands together to get the DC4 on the orings.

Dane
1986 F250HD SC XLT Lariat 4x4 460 C6-Sold
1992 Bronco XLT 4x4 351W E4OD
1998 GMC Sierra SLE K1500 350 4L60E
Arizona

Gary Lewis

Re: Best Way To Seal Fuel Tank Opening

Administrator

I don't like the "if it doesn't work" idea.

This will be my third try and I want to ensure it does work.

I'm thinking about trying to seal the tank while I have it down and add 3 - 5 psi of air pressure to it and then spritz the area with a soap and water mix. Should be able to put air in via the vent, assuming the rollover valve doesn't pop out, plug the supply and return fittings, and hope the gas cap is truly sealed.

Thoughts?

Gary, AKA "Gary fellow": Profile

grumpin

Re: Best Way To Seal Fuel Tank Opening

Yes, I don’t blame you. I was assuming you could see the o ring if it popped out.

If you can get that pressure on it, I think that’s a good idea.

Dane
1986 F250HD SC XLT Lariat 4x4 460 C6-Sold
1992 Bronco XLT 4x4 351W E4OD
1998 GMC Sierra SLE K1500 350 4L60E
Arizona

Gary Lewis

Re: Best Way To Seal Fuel Tank Opening

Administrator

I can't see that the o-ring has popped out now and it leaks. So I want to test it before I raise it back up.

And, thinking about it, the silicone is the least "final" approach, meaning that if it doesn't work I can move on to the Permatex approach. So I think I'll start with that.

Gary, AKA "Gary fellow": Profile

HBF84

Re: Best Way To Seal Fuel Tank Opening

Aloha Gary,

My “patch job” of the filler tank hose where I sandwiched this permatex between the filler hose and a section of radiator hose (cut down its length to wrap over the filler hose) is still holding and no fuel is leaking when I fill up my tank.

1984 F-150 2wd short bed with 4.9L, 4 speed overdrive manual transmission, and 3.08 rear end (18) switched to the 3.55 limited slip (H9).

Gary Lewis

Re: Best Way To Seal Fuel Tank Opening

Administrator

Yes, that Permatex does really well around fuel. I've used it many times - and may again this time. We shall see.

Gary, AKA "Gary fellow": Profile

Gary Lewis

Re: Best Way To Seal Fuel Tank Opening

Administrator

Time for an update. I documented what I did in Big Blue's Transformation thread, but the short answer is that I used the Permatex Pipe Joint Compound. However, you should read how I tested it and what else I found.

I thank all of you for the input. But when I got in there and couldn't find a smoking gun I decided something more that silicone grease was needed.

Gary, AKA "Gary fellow": Profile