Sealing brass fuel system threads

[MarkT]

Having a hellofa time.  Trying to seal the brass threads of these fuel lines. The stacked bushings are the worst.



Can't seem to find a sealant that works with threads, for fuel with ethanol.  Products that claim to be specifically for that - still leak.  Read everything I can find on the interweb and checked youtube.

I have tried these products.  Note that several of them claim to be for sealing pipe threads against gasoline with ethanol.  Today's effort, is with Permatex Aviation Form-a-gasket #3 - the bottle, bottom right. Replaced the bushings and nipples with new, and smeared it on the threads, mail and female, let it set for 7 minutes, then assembled with correct torque.  This is the product the so-called pros go to for this exact situation.  Don't know if it will work yet.



I almost got a soln with the Permatex Form-A-Gasket Sealant, bottom center.  Meaning the leak is really slow.  But still leaks.  The bottom row all claim resistance to auto fuels including ethanol.
I'm resisting using yellow PTFE tape.  It's really for gas, not gasoline with ethanol per my readings. And can cause a problem if a chunk breaks off and gets in the carbs.

Gotta think I'm doing something wrong but I'm not finding anything that helps online.

[The emperor has no clothes]

I used the yellow tape when I put the DanMarc on. No issues for a couple years now. Just make sure the tape is down 1 thread from the end.

[98valk]

tape or pipe dope.  for that application I prefer tape.  The threads of the fitting ALWAYS do the sealing. The tape or other thread sealant actually does very little and should never be relied upon to seal bad threads/joint. Unless u use a specific thread sealant by Loctite (owned by a foreign company now) which is a glue/thread locker. http://na.henkel-adhesives.com/industrial/thread-sealant-14405.htm. (currently reviewing a repair standard at work and just reviewed a lot of their products which were called out for use)
  The tape for example is actually being a lubricate which allows the threads to engage deeper to seal without galling the threads. Galling prevents full engagement of the threads to seal the joint.
if using the tape just keep it at least three threads from the end.
Last I read, and one of the engineers I work with actually told me first, that there really isn't a difference btwn white and yellow tape now. All white tape is the same as yellow tape now. new law or something require this a few yrs ago.

[John Schmidt]

I also have had good luck using the tape, but as suggested I keep it a few threads from the end.

[Blackduck]

#3 should be fine, have used it many times for thread sealing.
If not working then use Loctite 567, sealant with Teflon.
You do not have to over tighten and they will still come apart easily if needed.
Have used with compressed air, Nitrogen and Natural gas up to 4000 PSI.
Cheers Steve

[da prez]

  A dry seal pipe thread is good for only one tightening according to my past learning. A pipe thread has what is known as truncation , it is the amount of open flat at the crest and root of a dry seal thread. There is also a straight pipe thread. It is very common on a coupling. As for your leak , there is a pink Teflon tape that is used for natural gas sealing. I have a can of aviation grade permatex sealer which I use in a lot of situations. Let it tack up a little and then put the threads together. As stated earlier , avoid sealer on the first thread or two.
   B T W , I, like everyone else, will reuse a pipe thread as it cost to much to get new for a project.
 Try the sealers and good luck.

                                                     da prez

[MarkT]

Follow-up:  It's still leaking fuel slowly with the Permatex Aviation Form-a-gasket #3.  I don't get it.  I followed instructions as accurately as I can, and searched online for any otherwise undocumented tips. The Permatex site is unreachable on my computer for any official instructions.  This stuff is supposed to work, according to all reports I can find.  Not failing just with the one product, but with every Permatex product I tried, as well as TFE paste. So what is going on?  Do I have to let the stuff get REALLY sticky before assembly?  Perhaps wait a week for it to set up before using it?

I'll give the yellow tape a go.

EDIT:

Got into their web site finally.  Now they are saying threadlockers are the way to seal threads from leakage.  OK.  I have all colors threadlocker, I'll use the blue .  But I'll try the yellow tape first.  Not feeling the love from Permatex though I've used their products for decades for gasketing.

I'm thinking the problem comes from the ethanol.  I note I can clean up the stuff off my hands with alcohol.

[Tailgate Tommy]

Back 40 years ago when I worked on motorhomes we used the GM stuff on the left on generator brass fuel line fittings and GMC motorhome air suspension fittings. Not sure about the stuff on the right.



Looks like this is what they have availale today:
https://www.amazon.com/Genuine-Fluid-12346004-Teflon-Sealant/dp/B000QIXFEE
Genuine GM Fluid 12346004 Teflon Pipe Sealant
An instant-sealing, low-odor sealant for all threaded connections. Repositionable up to four hours. Ideal for sensor installation, except oxygen sensors. Seals machine and tapered threads. Compatible with oil, water, and refrigerant.

You sure you don't have a hairline crack in a fitting?
Hope you find something that works.

[DK]

Are you using flare nut wrenches?

Using them minimizes distortion of the fittings.

[jim@98valkyrie.com]

Mark,
In a former life, I was a pipefittter and plumber. We used Rectorseal #5 on a lot of different fluids and gases. Check out the data sheet- it shows Unleaded gas with 10% alcohol. Here is the link:
http://ows.rectorseal.com/product-data/rectorseal-no-5/dsno5.htm

[Miker]

Use Gasoila dope. Always works. So does Locktite 567. As mentioned, maybe you have a cracked fitting.

[MarkT]

Mark,
In a former life, I was a pipefittter and plumber. We used Rectorseal #5 on a lot of different fluids and gases. Check out the data sheet- it shows Unleaded gas with 10% alcohol. Here is the link:
http://ows.rectorseal.com/product-data/rectorseal-no-5/dsno5.htm

Thanks I ordered a can.  Hope it works.

Are you using flare nut wrenches?

Using them minimizes distortion of the fittings.

The problem is not with the flare fittings on this fuel system (out of sight in the pic above).  It's with the brass threads, especially the stacked bushings.  The rest of the fittings sealed.

Back 40 years ago when I worked on motorhomes we used the GM stuff on the left on generator brass fuel line fittings and GMC motorhome air suspension fittings. Not sure about the stuff on the right.


Looks like this is what they have availale today:
https://www.amazon.com/Genuine-Fluid-12346004-Teflon-Sealant/dp/B000QIXFEE
Genuine GM Fluid 12346004 Teflon Pipe Sealant
An instant-sealing, low-odor sealant for all threaded connections. Repositionable up to four hours. Ideal for sensor installation, except oxygen sensors. Seals machine and tapered threads. Compatible with oil, water, and refrigerant.

You sure you don't have a hairline crack in a fitting?
Hope you find something that works.

Like I said, I think the problem is caused by the ethanol.  Note I said above, I replaced those parts with new and the problem remains, so no cracks in the parts.  40 years ago gasoline didn't have ethanol in it.  I never had these problems sealing fuel systems back in the day of gasoline sans ethanol.

Use Gasoila dope. Always works. So does Locktite 567. As mentioned, maybe you have a cracked fitting.

Also ordered a tube of 567.

[MarkT]

Went ahead with the yellow tape.  Not leaking at all.  Yet.  Knock on wood, I guess.