How would you seal up a threaded fitting in a valve cover?

As an experiment, I'm adding another vent to the driver's side valve cover on the Ford 302 in the Fubari.

It's a catch-can setup, so I used a plain-old 90-degree NPT to barb plumbing fitting, no muss, no fuss.

Even with a successful drill'n'tap and a tapered fitting, I have a tiny bit of oil weeping at the threads when I run the motor flat out.  I used the same white never-dry ARP sealant that I use for oiled bolts, like lower intake bolts.

I have a couple of oil-resistant high-temp silicone products I could try, but they're more oriented for gasket interfaces, not threads.

Teflon tape, in careful application so as not to expose much wrapping on the threads extending below the inner surface of the valve cover, is tempting.  But somehow, I have a nagging suspicion it's a bad idea?

I've used RectorSeal #5 for applications like that and haven't had any problems.  Most recently I used it on an oil pressure switch as a back-up to the teflon tape that was pre-applied to the sender's threads.

rectorseal....rectalseal...buttplug...fordjokes... nevermind. 

I would just use the thread tape. If a tapered fitting with thread tape on it doesn't seal you may have actual damage in the thread area.

Loctite 572 is my favorite. Really good automotive chemical compatibility. It's not cheap but neither are leaks of flammable liquids. 
https://www.grainger.com/ec/pdf/Loctite-572-Thread-Sealant-Data-Sheet.pdf

npt = tighten it more?

I have discussed my love for leak lock here before.

I can't imagine not having a tube in my tool box at all times.

rated up to 400f and 10,000psi Safe for  R-12, R-22, R-502, R-134A, etc., all CFC, HFC and HCFC refrigerants, petroleum products, natural and manufactured gases, steam, water, air, etc. Doesn't turn into a  loctite style glue so joints come apart easily.

Right Stuff.

Yes, that's my answer to everything.

No room for a bulkhead fitting?

edizzle89 said:

npt = tighten it more?

Nope, NPT will always leak without a thread sealant:

https://www.directmaterial.com/knowledge/npt-vs-nptf/

Teflon tape can work, that's what I use on the NPT-to-AN adapters on my oil cooler's sandwich plate.

The number of one-wire NPT threaded oil pressure senders that seal up ~70psi of oil but won't be able to ground through the threads and light the warning light if you put thread tape on them seems to run counter to that statement. If there's some other explanation for why those work, I'm open to it. I've never really had problems getting NPT to seal as long as you're engaging into some fairly deep threads. If you put a hole in a fairly thin material like a valve cover and you're only engaging 3 threads I can imagine that you wouldn't feel safe using the amount of torque that would get you a good seal if you were threading into a deeper hole. Just a thought. 

Vigo said:

The number of one-wire NPT threaded oil pressure senders that seal up ~70psi of oil but won't be able to ground through the threads and light the warning light if you put thread tape on them seems to run counter to that statement. If there's some other explanation for why those work, I'm open to it.

I always thought that oil pressure senders seal around the hole at the bottom of the "bolt," rather than at the threads.

Hmm - British cars use two types of hydraulic brake light switches - the ones that have pipe threads and the ones that seal against a copper washer. It is pretty standard with the former style to use teflon tape and I've never seen any grounding issues, although that is a logical question.

Vigo said:

The number of one-wire NPT threaded oil pressure senders that seal up ~70psi of oil but won't be able to ground through the threads and light the warning light if you put thread tape on them seems to run counter to that statement. If there's some other explanation for why those work, I'm open to it. I've never really had problems getting NPT to seal as long as you're engaging into some fairly deep threads. If you put a hole in a fairly thin material like a valve cover and you're only engaging 3 threads I can imagine that you wouldn't feel safe using the amount of torque that would get you a good seal if you were threading into a deeper hole. Just a thought. 

The brass threads deform to conform, I think.

What size NPT? 

The larger the pipe thread size the greater thread depth engagement required.

Teflon tape worked.

There's now a tube of Leak Lock in my box, for next time.

Sucks though, I still have crankcase vent problems above 5,000 rpm under high load.  The rings are new and compression is +/- 10% of 145 psi on all 8 cylinders.  I'm guessing the bores are JUST enough off that they can't keep a perfect seal when things get going really rough.  Still a great street motor, at least.

Time for a new bottom end.

JBasham said:

Teflon tape worked.

There's now a tube of Leak Lock in my box, for next time.

Sucks though, I still have crankcase vent problems above 5,000 rpm under high load.  The rings are new and compression is +/- 10% of 145 psi on all 8 cylinders.  I'm guessing the bores are JUST enough off that they can't keep a perfect seal when things get going really rough.  Still a great street motor, at least.

Time for a new bottom end.

Have you done a leakdown test?

noddaz said:

JBasham said:

Teflon tape worked.

There's now a tube of Leak Lock in my box, for next time.

Sucks though, I still have crankcase vent problems above 5,000 rpm under high load.  The rings are new and compression is +/- 10% of 145 psi on all 8 cylinders.  I'm guessing the bores are JUST enough off that they can't keep a perfect seal when things get going really rough.  Still a great street motor, at least.

Time for a new bottom end.

Have you done a leakdown test?

I had this same problem on an s bc on the track.  It had 1 large vent from 1 valve cover.  I had to vent both valve covers because it would blow by on turns opposite the vented valve cover.  

1 vent from each valve cover solved it.

I would drill and tap for a AN fitting with a “O” ring or use a AN Bulkhead fitting with “O” ring and nut if valve cover is too thin to get enough threads to engage properly.  Unless valve cover is pretty thick it doubtful you can get enough threads for tapered NPT fitting to seal properly with or without Teflon taper pipe dope. My two cents.