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Fuel proof NPT thread sealant

Good 'ole Aviation Form-a-Gasket (brown Permatex) is hard to beat...but there are dozens of choices.
 
LOCTITE 567 is another choice, and is what I use on fuel and oil NPT fittings
No issues to report
 
Another vote for Locktite 567 here.. whatever you do, don’t use fuel lube as a sealant! Too many people have, and it works for a little while, but it’s a lubricant, not a sealant, and eventually, it will leak, and the next person has to take apart every fitting and reseal it!
 
Taltruda said:
Another vote for Locktite 567 here.. whatever you do, don’t use fuel lube as a sealant! Too many people have, and it works for a little while, but it’s a lubricant, not a sealant, and eventually, it will leak, and the next person has to take apart every fitting and reseal it!
Click to expand...

Yes, no fuel lube - have been there! Resealed with Locktite 567.
 
DanH said:
Good 'ole Aviation Form-a-Gasket (brown Permatex) is hard to beat...but there are dozens of choices.
Click to expand...

Yep of ole #3. The only thing I know will dissolve it is alcohol.

I have switched to 567 for things it didn't do well.

BTW - I have 140+ 1/2" NPT joints on my 175pis air system sealed with #3 and still don't leak after 30+ yrs.
 
Pro seal

Pro seal works great for applications that do not need to be disassembled.
There are a few select places where Pro seal is a very good choice.
Loctite type sealers are much easier to use though and available everywhere.
 
Form-a-Gasket #3 is a non-hardening resin sealant. It doesn't form solid chunks, and dissolves with plain isopropyl alcohol.

https://www.permatex.com/wp-content/uploads/tds/80019.pdf

567 is an anaerobic methacrylate adhesive, the same family as Loctite/Permatex threadlocker products. It cures to a solid, and dissolving it requires a Loctite solvent.

https://datasheets.tdx.henkel.com/LOCTITE-567-en_GL.pdf
https://datasheets.tdx.henkel.com/LOCTITE-SF-768-en_GL.pdf

Mostly we use aluminum fittings, sometimes in tight places, so increasing the removal torque isn't a plus. It's already too easy to round the flats, and they're often screwed into fragile things. In addition, female threads should be cleaned before reassembly, so old sealant isn't pushed into the fluid line.

Like Bill, I too have some 567 in the sealant bin for specific applications, and yeah, it's good stuff. However, it's rarely used for anything I may want to take apart in the future.
 
I thought you weren’t supposed to use anything on npt seals except the torque of the fitting. What am I missing?
 
nohoflyer said:
I thought you weren’t supposed to use anything on npt seals except the torque of the fitting. What am I missing?
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You have to use sealant on NPT (Tapered Pipe Thread), otherwise it will leak.

Permatex #2 and/or Locktite 565 (or 567 or 592). Apply sealant 2-3 threads from the "front" (opening) of the nipple.
 
RTFM?

Use the manual?

:confused:
 

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nohoflyer said:
I thought you weren’t supposed to use anything on npt seals except the torque of the fitting. What am I missing?
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You don’t use any sealant on the “flare” side of the fitting.. this is because the sealing occurs on the 37degree flair. You DO use sealant on the pipe threads (the tapered threaded part) as there will be a leak and/or thread seizure with a leak if you don’t.. many oil coolers have been destroyed by dry fittings, only to have the threads leak and seize then gaul upon removing..
 
For most RV sized pipe fittings you ideally engage say 6-7 turns total. Maybe 3-4 turns by hand. With something like Loctite 567 anything close to that will work. If I find a fitting that will only engage 2 turns by hand or more than 4 I expect trouble.
 
Disagree

DanH said:
Form-a-Gasket #3 is a non-hardening resin sealant. It doesn't form solid chunks, and dissolves with plain isopropyl alcohol.

https://www.permatex.com/wp-content/uploads/tds/80019.pdf

567 is an anaerobic methacrylate adhesive, the same family as Loctite/Permatex threadlocker products. It cures to a solid, and dissolving it requires a Loctite solvent.

https://datasheets.tdx.henkel.com/LOCTITE-567-en_GL.pdf
https://datasheets.tdx.henkel.com/LOCTITE-SF-768-en_GL.pdf

Mostly we use aluminum fittings, sometimes in tight places, so increasing the removal torque isn't a plus. It's already too easy to round the flats, and they're often screwed into fragile things. In addition, female threads should be cleaned before reassembly, so old sealant isn't pushed into the fluid line.

Like Bill, I too have some 567 in the sealant bin for specific applications, and yeah, it's good stuff. However, it's rarely used for anything I may want to take apart in the future.
Click to expand...

I have used 567 on everything, and have never had any problem getting the fittings apart when needed, even after several years of use. Not sure of "harden to a solid" as it is still pliable after several years...
 
Some fittings may be hard to clock in the direction you want. If that happens, I will try a different fitting. For some reason, manufacturing tolerances or processes, a different fitting may work better.
 
rvbuilder2002 said:
Thanks for posting the link Bob

I think that is the very same article that was used as research reference when the NPT fittings sealing recommendations chapter was added to Section 5 in the construction manuals.
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This is a great explanation. The one thing I did notice that is different than the reference I think I’ve seen on Van’s site is the amount of tightening past finger tight. If I recall correctly, the Van’s reference said 1/4 turn past finger tight, whereas the link above says finger tight plus 1-2 turns. Is the difference aluminum vs steel?

Edited: Just so my “well duh” moment doesn’t trip anyone up - don’t be like me and talk about the NPT and flared fitting in the same breath just because in your head you’re picturing a fitting with both. As Scott points out below, those are two different beasts with different requirements.
 
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skelrad said:
This is a great explanation. The one thing I did notice that is different than the reference I think I’ve seen on Van’s site is the amount of tightening past finger tight. If I recall correctly, the Van’s reference said 1/4 turn past finger tight, whereas the link above says finger tight plus 1-2 turns. Is the difference aluminum vs steel?
Click to expand...

I think you may be confusing the B nut that is on a flared line fitting versus NPT threads.
There is a difference between the two.
 
What's the difference?

bjdecker said:
You have to use sealant on NPT (Tapered Pipe Thread), otherwise it will leak.
Permatex #2 and/or Locktite 565 (or 567 or 592). Apply sealant 2-3 threads from the "front" (opening) of the nipple.
Click to expand...

In a previous thread (no pun intended), everyone was all about 565 for keeping the threads sealed, especially fuel drains. This thread is all about 567. :confused: What are the differences and where are each used? Are they interchangeable? Curious (confused) minds want to know.....:confused:
 
Roadjunkie1 said:
In a previous thread (no pun intended), everyone was all about 565 for keeping the threads sealed, especially fuel drains. This thread is all about 567. :confused: What are the differences and where are each used? Are they interchangeable? Curious (confused) minds want to know.....:confused:
Click to expand...

This doesn't answer all of your questions but according to what's stated in this older thread, 567 has a higher temp rating than 565.
 
Roadjunkie1 said:
In a previous thread (no pun intended), everyone was all about 565 for keeping the threads sealed, especially fuel drains. This thread is all about 567. :confused: What are the differences and where are each used? Are they interchangeable? Curious (confused) minds want to know.....:confused:
Click to expand...

Yup, the 565 is great.. 567 is the same with a higher temp rating.. I don’t think there’s a place where you NEED the higher temp rating, but it can’t hurt..
 
Taltruda said:
Yup, the 565 is great.. 567 is the same with a higher temp rating.. I don’t think there’s a place where you NEED the higher temp rating, but it can’t hurt..
Click to expand...

Which is why 565 is the one on the list of recommended sealants in Sect 5 (Par 5-27) of the construction manual.
 
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