SPECIALIST NEEDED - 351 C Oil system

Team,

I have a question about the screw in plug on the side of the block above the fuel pump.

I tried priming my engine before first start the other day and found a puddle of oil below the car.  I traced the leak to the screw in plug on the side of the block just above the fuel pump.  I tried tightening the plug, but it just goes deeper and deeper without ever seating.  (Top of the plug is recessed about 1/8 to 3/16 deep from flush now.  So here are my questions.

1) Should a certain sealer be used on the threads of that plug to help seal the threads under operating pressure?

2) Is the thread supposed to be a straight thread, ot a tapered(NPT) thread?

3)  Is there any chance I could thread the plug in too far, and restrict oil flow to the top of the engine?

After threading the plug in farther, the leak seemed to stop, but I am concerned about when the engine is running at thousands of RPM's versus the slow RPM I was driving the pump to prime the system.

Your help is appreciated!

kcmash

1) I like Permatex #2

2) tapered pipe thread

3) Yes

1) Should a certain sealer be used on the threads of that plug to help seal the threads under operating pressure?

2) Is the thread supposed to be a straight thread, ot a tapered(NPT) thread?

3)  Is there any chance I could thread the plug in too far, and restrict oil flow to the top of the engine?

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1) NPT threads don't often need sealant, but if you desire you can use some Teflon thread tape or liquid Teflon sealant. 

2) It should be a 3/8" NPT plug.  The hole has a taper as does the plug so they get tighter when screwed together.  Wondering if someone installed the incorrect style plug and that's why it's going in too deep. 

3) You would need to run that plug in WAY deep to have it restrict anything.  I don't even think its possible as it intersects the main pressure passage from the oil filter to the entire engine.  It would be easily noticeable as you'd starve oil to the entire engine, not just to the top end.

1) Should a certain sealer be used on the threads of that plug to help seal the threads under operating pressure?

2) Is the thread supposed to be a straight thread, ot a tapered(NPT) thread?

3)  Is there any chance I could thread the plug in too far, and restrict oil flow to the top of the engine?

Click to expand...

1) NPT threads don't often need sealant, but if you desire you can use some Teflon thread tape or liquid Teflon sealant. 

2) It should be a 3/8" NPT plug.  The hole has a taper as does the plug so they get tighter when screwed together.  Wondering if someone installed the incorrect style plug and that's why it's going in too deep. 

3) You would need to run that plug in WAY deep to have it restrict anything.  I don't even think its possible as it intersects the main pressure passage from the oil filter to the entire engine.  It would be easily noticeable as you'd starve oil to the entire engine, not just to the top end.

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OK thanks!!!   I don't want to find out the hard way that I starved the engine of oil.

2)  I am confused on the NPT.  A straight plug should not thread in without a lot of slop, and an NPT should tighten after a couple of turns.  I thought about backing it out and using the Teflon tape.   As far as "Someone" installing the wrong plug, that would be me if anyone.  I have been in a long term restoration on this thing and bought this engine to assemble and install.  The plugs were misplaced somewhere over the years so I went to an autoparts store and got the NPT plug kit to solve my problem.  I will take another swipe with the allen wrench to see if it will snug anymore.

What do you think about using oil pan gasket sealer on the threads versus teflon?  That stuff has the correct oil and gas properties, where I am unsure of the NPT Teflon tape chemical compatibility.

kcmash

the sealer u are asking about is it a brush on or rtv ?? i use a cooper based thread lube on just about everything. u can use most anything as long as u don't goop it on. not sure on the 351C but my 302 that is where the oil pressure sending unit goes. just put it on if you'r going to use one there. u might want to put a 6" pipe in with a gage attached so u  know of pressure.

I just took a look at mine. It sticks out about 3/16" from the block. Although it is covered with paint, I'm 99% sure it should be 3/8 NPT.

I got "fooled" by a thread on a spare block where the water temp sensor fits. It looked all the world to be 5/8 x 18 thread and even a thread gauge appeared to confirm it, BUT no, it was a rusted thread. I thinking that perhaps someone used a 5/8x18 plug and used sealant to 'make it fit'

I would go buy a 3/8 NPT hex socket plug and try it. (or anything 3/8 NPT threaded at that point) You might need an NPT tap to clean out the old gunk first.

On sealant, yes, make sure it is oil resistant. Permatex 2 should be ok I think, but check.

Good luck,

Geoff.

I would suggest any teflon based brush on type thread sealant, I typically use a permatex brand, teflon based on all pipe threads brushing it only on the male threads.

Thanks, Jay

I would suggest any teflon based brush on type thread sealant, I typically use a permatex brand, teflon based on all pipe threads brushing it only on the male threads.

Thanks, Jay

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