Thread Sealant for Fuel Line Fittings

[Bingster]

I have a combination of compression and standard fittings for connections from the carb to the fuel pump.  Should I put a thread sealant on any of them?

[Los_Control]

I think it depends on the fitting. If it has a flare on the male end, a seat on the female end .... no sealant.

My new gas tank requires a 1/4" bushing to adapt it to the 5/16" fuel line .... that requires a sealant.

 

I have a old school glass fuel filter in front of my carb. It has fittings on it for the fuel line to connect to ..... The fittings need sealant, the lines going to the fittings do not.

 

Does that make sense? .... The bushing in the tank needs sealer .... the line going into the bushing does not.

The fittings going into the fuel filter needs sealer, the fuel line going into the fitting does not.

 

Sadly I had same issue on my brake lines. I had a 5/16" T that one end needed to be converted to 1/4" .... The bushing going into the T needed sealant .... the brake line going into the bushing did not.

Just depends on the fittings you are working with. There is no answer one size fits all.

 

I would only use sealer where it is needed on fuel or brake lines.

 

[Sam Buchanan]

If the seal is dependent on tight threads, use sealant.

 

If the seal is dependent on a tightly fitting flare, sealant on the threaded nut holding the flare together is not needed, the threads aren't forming the seal.

 

A highly regarded sealant:

 

 

[Bingster]

Thanks!!

[D35 Torpedo]

I always use thread lock for any NPT

[kencombs]

To echo and maybe clarify, compression and flares do not seal on the threads so no sealant needed.  NPT seals on the thread so use sealant if needed.   But, judiciously so that none is allowed to enter the fittings opening.   I try not to have any on the first one or two threads.  

[Marcel Backs]

To prevent any danger of sealant breakdown, Teflon tape works wonders. M

[Bingster]

Gasoline doesn't break down Teflon tape?

[soth122003]

Yes it does. There is a type that is fuel resistant to be used in those areas.

 

Joe Lee

[Bob Ritter]

They have Teflon tape resistant to gasoline, it is yellow in color and works great...

[Bingster]

Buy it at an auto parts store?

[kencombs]

41 minutes ago, Bingster said:

Buy it at an auto parts store?

Plumbing aisle of Lowes or HD.   Speced for natural gas an propane piping.

[Sniper]

Natural gas and propane aren't gasoline.  I haven't had any issues using plain old white teflon tape on gasoline fittings, or nat gas and propane for that matter., lol.

 

https://www.oatey.com/products/oatey-yellow-gas-line-ptfe-thread-seal-tape--1863212606

 

In any case, the biggest complaint about teflon tape, of any color, is that it can get onto the fuel system and clog things up.  But that is more of a issue on how the tape was applied.  You don't wrap the tape over the end of the fitting.

 

 

[Sam Buchanan]

What is overlooked many times is NPT fittings are designed to provide a seal via interference between the threads on the male and female parts of the connection. If the threads perform as designed no sealant is needed. In order for this interference fit to occur the male and female threads must be free of imperfections and torqued to the proper spec. But these fittings are mass produced and often the threads do not form the interference interface as designed and we are reluctant to apply as much torque as is needed to overcome the imperfect fit. There can also be difficulties in achieving full interference fit if a 90* fitting needs to be clocked a certain way.

 

The main purpose of teflon tape is to serve as a lubricant so more torque can be applied to the fittings and the thread interference engaged. Use as a sealant is a secondary function of the tape and can assist in sealing without full interference torque being applied. Paste sealants work in the same manner as tape.

 

Care must be taken with the use of tape or sealant to assure nothing is introduced into fuel or especially oil passages because the tape or sealant won't dissolve once clogging a fuel or oil passage. Proper technique will prevent this failure and keep us from having a sad day.

Edited September 15, 2023 by Sam Buchanan

[kencombs]

2 hours ago, Sniper said:

Natural gas and propane aren't gasoline.  I haven't had any issues using plain old white teflon tape on gasoline fittings, or nat gas and propane for that matter., lol.

 

https://www.oatey.com/products/oatey-yellow-gas-line-ptfe-thread-seal-tape--1863212606

 

I

 

 

You're correct gas and gasoline are different things.  That said, the yellow tape was developed for gas lines.  It is much thicker, denser and stronger in order to resist the higher torque applied to fuel lines, as compared to smaller water lines the white stuff is normally used with.    And the white stuff is not approved for use with gas or propane per the NEC.   Some of the components of petroleum products apparently don't play well with the thinner white stuff.   

Truthfully, I don't use anything on first assembly as most fittings seal without it.   In the case of a bad one, I pull it out and use some sealer, but usually a thread locker type rather than tape or paste.

[Sniper]

I just wanted to clarify in case anybody was confused in regards to the term gas when used with the yellow Teflon tape. I remember years ago when I bought my first high volume fuel pump for a big block. The instructions were very clear not to use anything on the threads you could potentially crack the housing. Of course that is back when you can still buy American-made stuff that you know had quality built into it

[kencombs]

1 hour ago, Sniper said:

I just wanted to clarify in case anybody was confused in regards to the term gas when used with the yellow Teflon tape. I remember years ago when I bought my first high volume fuel pump for a big block. The instructions were very clear not to use anything on the threads you could potentially crack the housing. Of course that is back when you can still buy American-made stuff that you know had quality built into it

Yep, the taper of pipe threads can crack castings, especially aluminum or offshore 'mystery alloys', if overtightened,    and any lube on the threads increases the risk.  

[rallyace]

I use Rector Seal #5 on any NPT threaded joints carrying a liquid. It is an industrial thread sealant and lubricant that has been used for decades. It is good for gases, gasoline, water or just about any other liquid found on a car. As was mentioned above numerous times, proper usage of a a thread sealant or lubricant is to make sure it does not enter the fluid stream. Always keep it off the first two threads of the male fitting and a little goes a long way.  Just my two cents worth.

[Vin's 49 Plymouth]

Permatex Aviation form a gasket.............

[Marcel Backs]

never "bottom out" tape or sealant. It should only be on the last 5 or 6 threads of the fitting and no more than 2 layers wound in the opposite direction of tightening so it fits over the threads better during this operation. Never bury the threads. M

Edited September 21, 2023 by Marcel Backs
slight brain fart