I have a fuel leak where the tube goes into the bottom of the gas tank. It is a aftermarket gas tank and I used a threaded brass nipple to go into it with a gas shut-off valve attached to it. I did use Permatex fuel resistant gasket sealer on the threads which are a pipe thread. It doesn't drip but it is just enough leakage to stink up the cab. I did empty the tank, disassemble, clean and reassemble, allowing about a week to cure. Any ideas on how to eliminate this issue?
It may be the threads or it could be the shut-off valve, I would remove the valve and cap the nipple, that way you can determine if the threads are the source of the leak.
1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy
The leak is definitely coming from the nipple that threads into the bottom of the tank. Definitely not the valve or where the nipple threads into the valve it is the threads on the tank where the nipple threads into
I would remove the pipe/valve from the tank and thoroughly clean the threads and inspect the threads in the tank and the pipe to ensure that they are clean and undamaged. If the threads are good, reinstall and tighten securely without any sealant on the threads. Clean, undamaged pipe threads are designed to seal without sealant if properly tightened. That is the magic of tapered threads. I use whatever grease that I have handy on the threads so that I can tighten them tighter than if the threads were dry.
1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission
There is a difference between NPT (National Pipe Thread) and NPTF (National Pipe Thread Fuel). Only the latter type is designed to seal without teflon tape or pipe dope. NPTF threads rely on an interference fit (metal-to-metal crush) where crests and roots deform into each other without sealant.Unfortunately it's nearly impossible to tell the difference between them. So definitely use pipe dope (Gasoilia is a recommended brand.) It's been rumored that some reproduction tanks had straight threads rather than tapered threads and are nearly impossible to get sealed. If that's the problem with your tank, you MIGHT be able to run an NPT tap thru it and get a little taper in the threads. You'd still need to use pipe dope to get it to seal.
Kevin 1951 Chevy 3100 work truck Follow this saga in Project Journal Photos 1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car) Busting rust since the mid-60's If you're smart enough to take it apart, you darn well better be smart enough to put it back together.
Well, Kevin, you learn something every day! NPTF. I looked it up and even AI knew about it. Makes me feel dumb ! ( with a B )
~Charley 1954 Chevy 3100 with 235 “Bud” Follow along in the DITY 1963 Chevy half ton stepside short box 230 1954 GMC 3 ton 302 And several more Chevy camper and work trucks 1979 1987 1996
Yes, I think you hit it as the tank thread looked straight. I will burn off 10 gallons of gas and try your suggestion. I will post the results, might take a few weeks tho. Thanks for the input
