Sealing NPT fuel fittings

[curtis73]

I'm upping to a Carter electric fuel pump with 1/4" NPT fittings. The directions say that if I use any sealant on the threads it will break the pump. How do I get NPT to seal without any dope on the threads?

[Wizard29]

I would think a couple wraps of teflon tape would be fine.

[BrendellaJet]

Id use the teflon tape or the liquid stuff. Just be sure to leave the first few threads clean.

[Oldsquirt]

NEVER use teflon tape on fuel system fittings. Way too easy for that stuff to find its way into the lines, no matter how careful you are. They shouldn't leak if assembled dry, assuming you are using decent quality fittings. If you are afraid to try that, use some teflon paste....very sparingly, and keep it away from the ends of the threads.

[roostwear]

Use the liquid teflon sealer starting on the 2nd thread from the end and go around 1 1/2 threads. Assemble as normal, and don't overtighten! That's it.

[Kindsvater Flat]

I would think a couple wraps of teflon tape would be fine.
Teflon tape is to slippery and easily fittings can be overtightened and end result splitting the alum housing. For steel its fine but for brass or alum the paste is the only way to go.

[curtis73]

OK, paste it is. Thanks.

[Wizard29]

I'll respectfully disagree with the use of Teflon tape in this application.
My company manufactures machines that are used in the manufacturing of circuit boards. Our machines use many types of harsh chemistries as well as alcohol. Some of these machines perform cleanliness testing of circuit boards and as a result, it is absolutely critical no foreign contamination be introduced into the system.
We've done extensive research on the use of Teflon tape vs. the paste on steel, brass, aluminum, stainless steel, and plastic fittings. In every case when applied properly, the Teflon tape on NPT fittings is the best way to go. It yields zero system chemical contamination and zero system particulate contamination. With the paste and other types of sealers, we have noted a slight bit of "leeching" into the system, which has thrown our readings off. In high pressure and extreme plus and minus temperature tests, we have also seen some (not all) pastes leak.
The key words here are "applied properly." If you don't leave a couple of threads at the beginning of the fitting exposed, you may very well see pieces of tape in the system. If you overtighten, you may very well crack the fitting you are working with. The same can happen with paste - pay attention.
If you want some really kickass stuff, I just specified for use a really neat nickel impregnated Teflon tape that seals just about anything you can throw at it.
The bottom line is that we trust the Teflon tape to be an integral part of machines that help manufacture boards that are used in aircraft and space applications. That being the case, I'd certainly trust it in my fuel system. But, to each their own...

[Rexone]

I'll have to go with Wizard on this. I've used teflon tape (applied properly) on fuel fittings for years with zero issues.
Just make sure when you remove the fittings you take a small pic and get the tape rems out of the female port before reinstalling another fitting. Tape rems or strands inside the fuel system aren't good. Be careful as he said and you won't have problems.
I've also used the paste products. They work too but also must be applied properly as to not cause particulate comtaminates in the fuel system after the paste drys. I've also seen them leak and they can break delicate fuel pump castings just as easily as tef tape if fitting is overtightened.

[steelcomp]

OK...I'll offer my .02 here...Wizzard and MIke, you're technically correct in that the teflon tape, when properly applied, works fine. However, we're not talking about some high tech system where "particular or particulate contamination" is of any concern here. I meam, c'mon...this is a freekin fuel sytem on a boat, with probably more contamination in the fuel itself than anything that a little teflon paste is going to hurt. Gasoline will dilute and disolve that stuff in a heart beat, whereas even a small piece of teflon tape can get lodged in a needle and seat or jet and cause havoc. IMO, unless you've worked with enough teflon tape to be able to get it on the threads without any getting into the system, then by all means, use the goop. A little "particualte contamination" will be the least of your worries. (Makes me want to see the bottom of the fuel tank, if that's the worry) It's also a real good idea (read- mandatory) to flush out any system that you put any new fittings on, of any kind, before the engine is run. Wheather you flush out the pump before you install it, or you just run a gallon or so of fuel through the lines before you hook them to the carb, the system needs to be cleaned out. This will eliminate 99%of the potential problems you'll have. :D
One other thing...on tapered threads, the purpose for teflon anything isn't really to seal, but more to lubricate. The taper in a tapered pipe thread is suposed to act as a mechanical seal, and the teflon whatever, just allows easier tightening to make sure that the taper seals.

[cfm]

I use paste myself.
I talked with a fitting company once and he pushed to use Loctite, I believe blue. Just a dab across a few threads of course. 2-3 threads up as starting point.
1/4" fittings on a fuel pump ? Stepping up ? Or is this a lower medium to stock build ?

[Rexone]

steel I agree the taper is designed to do the sealing. But the problem with these whimpy aluminum fuel pump castings there is a fine line between not leaking and breaking the casting. You can't tighten them to specs that the threads were designed to seal at so you must have the additional sealing properties of either tef tape or paste to assist. Not just for thread lube. Tightened to the specs of a steel application which will seal from the taper design you'll bust the aluminum casting every time especially on Holley electrics and other with thin wall around the threads.
It's boggled my mind for years why all the fuel pump manufacturers (some oe pumps do) don't all go to inverted flare with straight threads for the seal. Carbs have em, why not fuel pumps? No goop required and no taper to break the delicate castings. AN adapters to inverted flare are readily available and / or could be easily made to any size AN hose desired.
But what the hell do I know lol. :)

[Rexone]

I use paste myself.
I talked with a fitting company once and he pushed to use Loctite, I believe blue. Just a dab across a few threads of course. 2-3 threads up as starting point.
1/4" fittings on a fuel pump ? Stepping up ? Or is this a lower medium to stock build ?
Locktite threadlocker isn't designed to seal fluids. They make a product called PST which is tho. Threadlocker might get the job done in a low pressure ap but isn't it's intended use, which is to lock threads together.
1/4 is small for anything more than stock ap. 3/8 NPT allows use of a -8 or -10 which will flow much more than -6 typical of 1/4 NPT.

[curtis73]

1/4" fittings on a fuel pump ? Stepping up ? Or is this a lower medium to stock build ?
1/4" NPT will supply a lot more than the 300 hp I'll be making. I have it all installed (minus the actual tubing and hose). The filter/water separator is on the transom immediately behind the tank, then the pump is on its bracket mounted to the rear of the port side head. If I had my camera I'd take a photo but I just don't right now. Wife took it on vacation. The nice thing about it is that from the tank to the filter to the pump there won't be any piece of hose that is longer than 18". From the pump to the carb will be 2' or so. I installed all the fittings on the tank and filter using the paste and taking all the precautions you folks mentioned. I installed the pump fittings with a little oil and cautiously torqued them home. I don't have much confidence in them not leaking, but the worst that could happen is I galled the fittings and I'll replace them with teflon paste. The other thing I realized is that all the fittings except one are not pressurized. The pump is the last thing before the carb so its just the pump outlet that I think would cause any real trouble.
I've also decided how I'm going to wire it and you tell me if this sounds right. I'm going to use a relay with hot power to the switched side and on to the pump, then ignition into the low side and ground the relay on the oil pressure switch. I had a pressure switch sitting around that is normally open/closes with pressure, so the pump won't run unless the engine has oil pressure. That way if the engine loses pressure it can only run as long as the bowls hold out, and if it stalls or if I have the key on its not constantly running. Sound good? The only fault I see with that is for my first start up and anytime I run the tank dry I'll have to artificially ground the relay to get fuel to the carb to start it.
I've also decided (at least for now) to use all hose and no hard tubing with the exception of a nipple on the carb since they're such short runs. Your thoughts?

[Wizard29]

Loctite does make thread sealers though. We have used Loctite 545 and 567 with decent results on some machines.
Both are quite expensive. The 545 is more, but seems to go "further" than the 567...

[Oldsquirt]

Now that I'm home from a long day of fixing people's cars and trucks, something I've been doing for 28+ years, I'll go a little further into my perspective on this.
Unlike you guys, I HAVE SEEN the damage that can be done by something as small as a 1/2" long stray thread of teflon tape. It has ranged from something as simple(on the surface) as a stuck open needle & seat causing a flooding condition(more times than I can count), to a partially plugged EFI fuel injector, to an engine that burned a couple pistons due to a lean condition brought on by a thread of that stuff actually making its way past a main jet only to block fuel flow into the booster(kid tried to "drive through it"). In every case, this damage was the result of an inexperienced individual using teflon tape to seal things that needed no sealant.
As pointed out, "proper application" is key, and it applies to everything. Most individuals who don't know what they should use are far less likely to get it right(without some supervision) than those who do it daily. Why even risk it when there are better options/solutions available?
I have NEVER seen any OE manufacturer use, or recommend using, teflon tape on fuel fittings. I have, on a few occasions, seen some sealant that looked a lot like threadlocking compound, but it was only on some pipe plugs in an EFI fuel rail.
If you guys are comfortable using the tape, go for it. You might, however consider trying the teflon paste as it is faster and easier to apply and isn't going leave any "loose threads".
I will continue to recommend dry installation as often as possible. If the fitting doesn't seal, then I will recommend the teflon paste. In 28 years on the job, I have NEVER used the tape on fuel system fittings and only rarely have I seen a need for any sealant at all.