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Old 02-21-2009, 01:03 AM   #1
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Default How do I seal NPT threads for Oil Sandwich?

Hi everyone,

I just got an oil cooler sandwich adapter with 3/8 NPT inlet/outlet. I got 3/8 NPT to -AN 8 fittings. What is the best way to seal up the thread on the NPT? I heard Oil will eat away at Teflon tape.

Thanks for the help.
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Old 02-21-2009, 01:25 AM   #2
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Here's the jist of it. NPT is tapered pipe threads. They have slightly different tapers as to cause them to seal when they meet. The teflon serves as a lubricant to allow the fittings to get much tighter than they would without it. As you tighten the **** out of it, the two tappers meet each other and the metals deform, crush-sealing against one another. Once they crush 360* around the threads, you now have 100% metal to metal seal that won't ever leak. No seals to blow, no gaskets to leak or blow, no sealant to leak. It's metal to metal sealing.
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Old 02-21-2009, 01:36 AM   #3
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um just srew em together no teflon or oil needed as pat said the metal seals on itself.
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Old 02-21-2009, 01:39 AM   #4
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Originally Posted by magnamx-5 View Post
um just srew em together no teflon or oil needed as pat said the metal seals on itself.
On steel to steel fittings you can get away with this. But not when using dissimilar metals, especially aluminum to steel. It will gaul up from from friction if you don't use teflon tape.
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Old 02-21-2009, 01:40 AM   #5
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ARP makes a special sealant goop for tapered pipe threads. IMO it works much better than teflon tape. i got some from summit a while ago.
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Old 02-21-2009, 08:36 PM   #6
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I typically use teflon paste.
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Old 02-21-2009, 09:43 PM   #7
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yeah on I remember reading on Injector Rehab that NPT use Teflon and AN don't...
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Old 02-21-2009, 10:22 PM   #8
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tapered threads get the sealant, compression fittings dont need it.

and teflon should be ok with oil... UNLESS you get it in the oil path and clog your ****. that's the big problem. if you do use teflon tape, keep it away from the openings.

you can also get that goop you put on and let dry first. mcmaster probably has it.
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Old 02-22-2009, 12:40 AM   #9
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What about that thick yellow teflon at home depot? The label says it's design for petroleum product, which I assume is meant for natural gas and propane lines.
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Old 02-22-2009, 02:29 AM   #10
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This stuff works awesome.
THREAD SEALANT, TEFLON, HIGH TEMP - 034 MOTORSPORT

The rest of the chemicals they sell are also the best I have ever used.
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Old 02-26-2009, 09:31 PM   #11
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Regular NPT fittings actually won't fully seal if you don't use some sort of tape or sealent, there is a gap between the crast and root of the threads that creates a spiral leak path. An NPTF fitting on the other hand will fully seal.

National pipe thread - Wikipedia, the free encyclopedia

Swagelok SWAK works very well, and there isn't the same danger of a chunk of tape coming free from the inside of the seal and going through your system.

MS-PTS-6 - SWAK® Anaerobic Thread Sealant, 6 cm3 Tube
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Old 02-26-2009, 11:47 PM   #12
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Quote:
Originally Posted by matttheniceguy View Post
Regular NPT fittings actually won't fully seal if you don't use some sort of tape or sealent, there is a gap between the crast and root of the threads that creates a spiral leak path. An NPTF fitting on the other hand will fully seal.

National pipe thread - Wikipedia, the free encyclopedia

Swagelok SWAK works very well, and there isn't the same danger of a chunk of tape coming free from the inside of the seal and going through your system.

MS-PTS-6 - SWAK® Anaerobic Thread Sealant, 6 cm3 Tube
realy? that must be why every suspension setup I've ever built with air bags , hydros or nitrogen never leaked. if new fittings are installed properly they should not leak at all. It's all about the deformation of the threads that seals them.
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Old 02-27-2009, 11:36 AM   #13
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i've had good luck with the thread sealant i got at pepboys or autozone or somewhere. it's in a white little tube and is rated for hydraulic use.
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Old 02-28-2009, 03:20 AM   #14
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realy? that must be why every suspension setup I've ever built with air bags , hydros or nitrogen never leaked. if new fittings are installed properly they should not leak at all. It's all about the deformation of the threads that seals them.
The Vast majority or "NPT" parts sold now are actually NPTF, and if any of the fittings are copper or brass or anything soft you can generally get a seal on either one, but if you are dealing with an actual NPT port and the port and fittings are steel you won't get a perfect seal. It's probably not really an issue in most automotive applications; my experience with it comes from high pressure (5000psi+) natural gas work. I'm just saying an NPT fitting was never designed to fully seal without some soft of sealant. If you are sticking an NPT fitting into the side of your engine, why not give it the best chance of sealing and stick some sealant on it. If it does nothing else, it will reduce the friction and galling letting you get the fitting in tighter for a given torque on it.
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Old 02-28-2009, 09:56 PM   #15
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I agree with you, the problem is most people don't know how to use the "sealants" properly. especialy teflon tape. which I reserve only for steel threads. I think most people would be better served getting a good seal in automotive applications by using new fittings and actualy running them in far enough to make a good seal rather than gooping on "sealant" or wrapping them with twenty turns of tape in the wrong direction.
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