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Old 11-22-2005, 12:44 PM
Maddmatt Maddmatt is offline
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Default Gas Tank Woes Pt. 2

-OR-

How to drive your 40 without feeling like puking.

So careful readers may remember my gas tank problems last summer. Short story, PO installed a poly tank. Even a quick read of IH8MUD will tell you that's not the way to go, but it is what it is. On the positive side, the space under the tank has obviously been repaired, and is now rust free.

Last summer I was tired of gas spilling out onto the passenger side floor on hot days, so I removed the sending unit and resealed it with RTV.

After a couple months the fumes were back, so I assumed my repair didn't work. At least the actual liquid gas hadn't reappeared.

Today I decided to fix it once and for all. I would love a brand new steel tank ($350 + tax from Boulder Toy, considerably less, but still pricey from Cdan) but only a month before Christmas is not the time to be dropping money on my truck. So I removed the seat and cover, and lo and behold my RTV repair worked! See pics below, and note the dust on and around the sending unit, indicating successful repair.

Now this other attachment to the left, (we'll call it "gas in") is the culprit. I'm going to unscrew it, add some RTV to the top couple threads, and screw it back in. Then I'll cover the bottom part with RTV. Hopefully have the same success as with the sending unit.

My question is: Does anybody know how the three brass fittings in the second picture are attached? Are they threaded as well? One of them appears to be leaking as well, and I'm just fishing for some first hand info. before I take them out. If they are some kind of pressure fitting, I'm just going to liberally cover them with RTV and be done with it, but if they screw out, I'll treat them the same as the "gas in" line.

Thanks for any help.
-Matt
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Old 11-22-2005, 04:43 PM
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subzali subzali is online now
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Just make sure your vent doesn't have a hole in it, that's part of the reason I almost rolled the truck the day I bought it! The other part was the exhaust coming in from my not-so-tight exhaust manifold
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Old 11-23-2005, 08:13 AM
leiniesred leiniesred is offline
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Default RTV on threads

I have found that RTV on threaded items just doesn't seal. Maybe you'll have better luck with the poly fittings, but on brass to brass connections, it doesn't hold air. I think it balls up in the threads and doesn't coat.

I've had better luck with either good old teflon tape or the teflon pipe joint compound in a tube.

Last edited by leiniesred; 11-23-2005 at 08:19 AM. Reason: spelling.
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Old 11-23-2005, 08:42 AM
Maddmatt Maddmatt is offline
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Do you think the thread tape will hold up to the gas? On the big one I'm not worried, it's plastic to plastic, so I'm pretty confident the RTV will hold. On the brass fittings, maybe I'll use thread tape, and then RTV over it? Thoughts or concerns?
Thanks
-Matt
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Old 11-23-2005, 12:21 PM
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Rzeppa Rzeppa is offline
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Teflon (what pipe thread tape is normally made of) does hold up to gasoline. However, pipe tape is not designed to make a seal on straight threads, only tapered pipe threads.

Silicone (RTV) does NOT hold up to gasoline. Do not use it on carbs, fuels lines or anywhere it will be exposed to aromatic hydrocarbon.

I will take a look at my 76 and 77 fuel tanks this weekend and see if I can offer any helpful suggestions. I suggest biting the bullet and going back to OEM. Everyone I know or have heard of who has tried one of those poly aftermarket tanks has had problems of various types. The most common being fumes from poor seals.
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Old 11-23-2005, 02:48 PM
Maddmatt Maddmatt is offline
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Thanks Jeff. If this doesn't fix it, it's back to OEM for me. Since my sending unit seal seems to be holding, I figured it was worth a chance. There's one type of RTV, 16b, that doesn't specifically say not to expose it to gasoline. It's what the guy at my local NAPA recommended last time, and what I used last summer, and it still looks the same as the day I put it on.

So I sealed gas in attachment this morning. I filled the top two threads with RTV, and then layed a bead around the top, screwed it in tight and put some more RTV.

I'll let it cure for a day or two before I fill it up and drive on some bumps. I'll post up the results here, either as a successful repair or a cautionary tale, depending on how it turns out.
-Matt
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