Having a problem with a fuel leak. Have an NPT fitting I can't get to stop leaking. I have tried TFE paste and Permatex #3 aviation sealant on the threads and still have a leak. Tried 3 different fittings also and all leaked. Any suggestions on a different sealant? Changing out the housing is the last resort.

options would be to tap it out to the next size larger NPT hole/fitting or JB weld the current one in there permanently (preclean it well) or as you said another housing.

Are you sure it's a TAPERED pipe thread, or maybe a STRAIGHT pipe thread. Same for the fittings.

I've always better luck with silicone tape on tough ones,,,like the fittings on my six pack's lines. Be careful to not allow into tubing.

I would use Teflon tape. I cannot think where you have NPT, unless on a electric fuel pump.

Thread Sealant

This will work. It is NOT just TFE paste but a true anaerobic sealer. You won't be disappointed.

This is the problem, it is not the sealer.

White Teflon tape should NEVER be used around fuel systems because when you take it apart it is near impossible to clean out all the little pieces.

Inverted flare fittings like on 6 pak fuel lines should never have any kind of sealer on the them, especially not teflon tape!


You should use WD 40 on them that allows you to get them tight and leak free.

Teflon(in error I had said silicone in earlier post) has always worked where paste has not. Also find tape more reliable for air compressor fittings.

I did note warning of never allowing teflon particles into tubing.

I did attempt old trick of using wd 40 on our six pack fittings to no success just as experienced with various paste type solutions. Teflon tape has worked successfully thru several carb removals and replacements(breaking down fuel lines at fittings much more reliable than removing fuel lines directly from carbs first for removal) I do throughly clean threads each time before reinstall, have experienced no difficulty doing so. Perhaps my fittings are a bit worn or for other unknown reasons teflon has worked the best for me. I believe the buildup of thickness using tape fills in the threads better,,,,not certain, just a guess.

Loctite 565 is also pretty good.

http://www.all-spec.com/Catalog/Adhesive...utm_content=PLA

The threads on an inverted flare nut are NOT intended to seal. The flare nut simply pushes the inverted flare against it's seat. If you ever can't get it to seal then the tube is not bent properly to allow the flare to seat square or the flare is bad. Fluid should never get past the flare. If it does then fix the problem. Never depend on any kind of sealer to fix what is a mechanical problem. Thread sealer is for tapered threads.


The original poster does not say what exactly he is trying to do. If he is trying to put a tapered thread into a straight thread or a flare fitting then it likely will leak no matter what.

It might help to know what your trying to seal up. As stated above you might be trying to seal a straight o-ring thread hole with a pipe fitting.

The threads are 3/8 NPT; not straight. I'm using a Russell an male to NPT adapter. The leak is at the NPT side. The housing is most likely not machined properly. The housing is from Tanks Inc. It bolts to the top of the fuel tank but the outlets, both pressure and return are NPT. Return sealed up just fine. I can install a new housing but I would rather exhaust other options first. NPT fittings should have sealant. I use Permatex #3 and never had any problems until now.

I assume you have tried other fitting, The next thing I would do is use a pipe tap to chase the threads , maybe a little deeper on the tap.

Ding ding ding we (may) have a winna. tapered deeper to get into some fresh threads (dont forget the sealer).

Having spent quite a few years dealing with high vacuum equipment where pipe threads are sometimes encountered they can sometimes be troublesome.
I found that using red or blue loctite always cured the problem unless there was a visible issue with the mating threads. Since then we have used it almost exclusively on NPT fittings.

Best stuff I've ever used is "Loctite 545"! Specifically made for thread sealing.

The mechanical/pipe fitter guys I worked with always used BOTH TFE sealant with tape over it. The Loctite 545 is awesome. I actually used The Right Stuff with success as well. I think I used The Right Stuff on my threaded nipples on my water pump for the heater hoses. On the aluminum adapters for the racecar I've always used TFE paste wrapped with Teflon tape in conservative doses.

Thank You for your inputs. I was able to fix the problem by using an extension and coupling and attached the NPT to AN fitting to the extension/coupling. Got the parts at the local ACE Hardware. This actually worked out good because now I can access the AN fittings without dropping the tank because they are about 3 inches forward now. If anyone ever uses a Tanks Inc tank on a B Body you will run into this also. I used Permatex 59214 thread sealant. Leak free so far.

The fitters I've worked with did the same thing. Once. After that I demanded they only use the anaerobic sealers. Pipe thread sealing is one area that, IMHO, where the 'belt and suspenders' approach isn't valid.