Sealing NPT in oil pan

[Curti]

What is the best way to keep oil from tracing down the pipe threads  when there is oil or grease on the other side.  A lot of torque doesn't seem to be the answer.

[Spinneyhill]

Somehow, you need to fill the space between the male and female threads. I have tried PTFE tape - no good; plumbers hemp - works with water but not oil; Loctite threadseal - works for a while, but absolute cleanliness is required at assembly and if you have to remove or tighten a bolt, the seal is lost. The differential cover and the oil pan bolts are all like this in the 1930 Dodge 8: one end in the oil, one end in the air.

[Curti]

Yes, I agree on all points. This is why I pose the question.  It is the engine oil pan drain that is really bugging me.

[joe_padavano]

1 hour ago, Curti said:

Yes, I agree on all points. This is why I pose the question.  It is the engine oil pan drain that is really bugging me.

 

What kind of engine? The drain plugs I'm familiar with are straight threads, not NPT. There is a seal washer that seals the bolt to the pan. If it is NPT, the tapered threads are the seal - metal to metal.  The teflon tape is only to fill small scratches and ease the removal - the threads need to wedge together.  If they don't, they may be excessively worn.  Also, be sure there isn't a hairline crack running from the hole in the pan. I've had a problem similar to that and it drove me crazy - more sealer and more torque just made it worse.  I finally found the crack.

[Guest]

NPT should seal all by itself.  My car is 88 years old with 500,000 miles.  Still the original pipe plug in the oil pan and the only time it leaks is when I don't tighten it enough. Using a 1/2 inch drive ratchet I have to tighten it almost to my maximum (probably close to 50 ft/lbs). Wipe the threads clean both in the pan and on the plug and it seals unless you have some other problem.  These tapered threads do wear.  Mine is worn enough that the plug goes in one thread more than it did in 1952.

Edited January 11, 2018 by Guest (see edit history)

[Curti]

The engine is a 1931 Auburn  Lycoming.  The threads are NPT in good condition ( maybe too good ) but they are wore to the point that the top of the plug  almost screws  into the pan.  I will try another plug.

[Bhigdog]

Try different plugs. There is a manufacturing tolerance. I just had a new furnace with 4 zones installed. Lots of NPT fittings. The plumber wrapped every thread with 4 turns of tape. Then he used the edge of the tape spool to press the tape into the threads. Then a liberal coating of pipe dope. I mentioned that looked quite time consuming. He said it was a lot cheaper than a leak. There were no leaks at all and the system is pressurized..................Bob

[PFitz]

Hardware store bottle of Teflon "plumber's paste" wiped into the threads by finger tip - end of leaks - both oil and fuel ! Has worked for me decades, even with messed up threads.

 

Paul

[Curti]

41 minutes ago, PFitz said:

Hardware store bottle of Teflon "plumber's paste" wiped into the threads by finger tip - end of leaks - both oil and fuel ! Has worked for me decades, even with messed up threads.

 

Paul

Excellent !    Thank you 

[Larry Schramm]

It is called Pipe Sealant with Teflon.  The GM Part number is 12346004.  Works great.

 

GM part on Amazon  https://www.amazon.com/Genuine-GM-12346004-Teflon-Sealant/dp/B000QIXFEE

 

 

[Frank DuVal]

The Teflon tape and Teflon pipe dope was an idea, that when I first heard about it, sounded like a terrible idea. Then I started having to use China NPT fittings in SS. They looked like they were cut with dull machine tools. Had a few leakers, so I tried the tape plus dope trick. Yes, it works well! Been doing it that way ever since on larger NPT fittings. On threads that look good, I just use Teflon (PTFE) dope. Also, if the fitting does not need to come apart, or can be heated with a torch when that time comes, we use a lot of epoxy (30 minute or so 5 minute too fast) to avoid leaks on NPT parts in R&D work. 

 

And of course, the warning if PTFE tape is used, keep the tape a thread or two back from the end of the male threads so tape "threads" do not get into the pipe and cause a clog in the system.

 

And, flare, inverted flare and o-ring sealing joints do not need any tape or dope on the threads, unless you just want the anti-seize properties.

 

For oil and gasoline service, I use a product called Gasoila. 

 

If the NPT threads are worn to the point of bottoming out, then one of the parts needs replacing. 

[JFranklin]

If the plug bottoms just use a gasket.

[Curti]

Thanks fellas ! I'll try some of that pipe sealant with teflon.

[Guest]

JFranklin a pipe plug has no flat surface, no place to put a gasket.  Tapered pipe thread is designed so that it doesn't need a gasket.

 

[Curti]

For oil and gasoline service, I use a product called Gasoila. 

 

 Frank, there is a lot of different 'Gasoila' products what would you suggest for the oilpan ?  I put PTFE tape on the plug yesterday.  It scares me to think a small bit of it getting loose and going thru the system., so I am going  to  use a  paste. 

[joe_padavano]

I've had a few instances of NPT threads that refused to seal with normal sealants.  Loctite 567 always solved the problem.  I strongly recommend it for difficult NPT threads. It's not cheap, but it works.

[Bhigdog]

Being the type of person that is rankled by temporary or stop gap solutions my fix would be to fix the problem. Assuming a steel oil pan I would cut out the NPT fitting and TIG or silver braze in a standard type female  drain fitting with a standard gasketed plug. End of problem..............Bob

[Frank DuVal]

I use the blue label stuff. I think it is before they put PTFE in it. I do see they offer the blue w/o PTFE. 

 

Either should work fine. When applying the paste, keep the first thread or so clean and you should have no issues of something coming loose and entering the oil.

[PFitz]

I don't recommend using the Teflon tape on engine and fuel system fittings. All too often, I've found little shreds of it (and silicon sealers) stuck in carb jets, and fuel and oil pump screens of my customer's engines.   The tape gets cut into thin strips by the edges of the pipe threads. When you unthread the fitting and then reinsert it, the strips can windup in places they shouldn't.

 

As long as you don't gob it on, what little amount of the paste that might get pushed in by reinserting the plug will not hurt the motor, or the fuel system. 

 

Anyone remember the slogan from the old Vitalis hair tonic ads ?

 

Paul

[Rusty_OToole]

I use teflon tape but defer to the more experienced who prefer paste. I will say, I would regard the pipe plug as disposable, or consumable, to be used up and replaced. If it is worn replace it with a brass one if you can find one. It will seal better and not wear the pan.