Oil pressure sending unit leak, 383 stroker - Chevelle Tech
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post #1 of 13 (permalink) Old Oct 7th, 15, 1:20 PM Thread Starter
Jim
 
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Oil pressure sending unit leak, 383 stroker

This is my first time on a forum and I'm really hoping to find a solution to my problem. I've got a '71 Chevelle with a 383 stroker that I recently did a lot of work on. Since putting the motor and tranny back in the car, I can't seem to get the oil pressure sending unit to stop leaking. It's a metal line going to a mechanical gauge, so it's modified from the original. The leak is coming from the brass fitting that screws into the back of the block by the firewall and next to the distributor.

I feel like I've tried everything. I've left it bare, used teflon tape, used pipe dope (which never dried?), and tried some black RTV. As far as I know, there was no leak from there before I changed the line and fitting.

I would really appreciate some help if anyone has ideas that I haven't tried. Thanks!
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post #2 of 13 (permalink) Old Oct 7th, 15, 3:06 PM
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Re: Oil pressure sending unit leak, 383 stroker

Jim - Remove the fitting and cap it off with a brass pipe plug and run it for a bit to verify that is the actual culprit. We use -AN fittings/hoses on our cars.
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post #3 of 13 (permalink) Old Oct 7th, 15, 3:59 PM Thread Starter
Jim
 
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Re: Oil pressure sending unit leak, 383 stroker

Thanks, Ill give that a shot
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post #4 of 13 (permalink) Old Oct 7th, 15, 4:14 PM
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Rob
 
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Re: Oil pressure sending unit leak, 383 stroker

That hole at the back of the block is 1/8" NPT, so you would need a male 1/8" NPT to a 1/8" male compression fitting to work with the copper or steel line.

The ARP sealant works well for the NPT fitting going into the block IF you take the time to clean it all up beforehand.

Stainless steel braided line using an NPT to -AN fitting would be a better choice here.

65 Chevelle 2Dr. Post,Global West stage 3, Small Block, Small Journal 337cid. Howards roller cam .570/.570" lift 227/233 duration @ .050 LS112, Speed Pro forged pistons 10 to 1, Trick Flow 195,23 degree heads, Holly 750 Ultra, Edelbrock Performer RPM air gap.

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post #5 of 13 (permalink) Old Oct 7th, 15, 4:45 PM Thread Starter
Jim
 
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Re: Oil pressure sending unit leak, 383 stroker

65chevelle300, that would be something that I haven't tried. I'm running 50-60 psi at idle. Is the pressure too high for a standard line?

Also, should the NPT to -AN fitting be brass, and you think that the ARP sealant would work well for that setup?

I currently have a brass 1/8" NPT fitting with the male compression fitting and a copper line. From what I can tell, the leak is coming from where the NPT fitting screws into the block.
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post #6 of 13 (permalink) Old Oct 7th, 15, 5:06 PM
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Rob
 
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Re: Oil pressure sending unit leak, 383 stroker

Well if the leak is from the NPT threads at back of the block then just removing the fitting and cleaning up all the threaded areas with solvent then using the ARP sealant should work fine. It might help to smear a very small amount of the ARP into the threads on the block and also on the fitting threads then snugging it down tight should work. I've never had them leak after doing that. This assumes you are using the correct size 1/8" NPT fitting going into the block.

As far as running oil pressure into the cab with a copper line, it should be ok but it's not something I would really trust to work long term.

Stepping up to I believe -3AN steel braid would be safer for that but getting around all the bends is trickier because steel braid doesn't like to bend very sharply at all so you would have to use longer bends and add some length to make up for it.

65 Chevelle 2Dr. Post,Global West stage 3, Small Block, Small Journal 337cid. Howards roller cam .570/.570" lift 227/233 duration @ .050 LS112, Speed Pro forged pistons 10 to 1, Trick Flow 195,23 degree heads, Holly 750 Ultra, Edelbrock Performer RPM air gap.

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post #7 of 13 (permalink) Old Oct 7th, 15, 5:40 PM
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Re: Oil pressure sending unit leak, 383 stroker

Plastic and copper lines have been used for this purpose for decades. Your problem is probably the compression nut and sleeve end of the line and not the NPT end. Pipe thread is self sealing. If the nut on the end of the line is over tightened it will crush the compression sleeve causing a leak.

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post #8 of 13 (permalink) Old Oct 7th, 15, 8:10 PM
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Re: Oil pressure sending unit leak, 383 stroker

Quote:
Originally Posted by oldcutlass View Post
Plastic and copper lines have been used for this purpose for decades. Your problem is probably the compression nut and sleeve end of the line and not the NPT end. Pipe thread is self sealing. If the nut on the end of the line is over tightened it will crush the compression sleeve causing a leak.
If you had read what he said in the first post, the leak was coming from the NPT fitting where it goes into the block and not the compression fitting which are not self sealing like you believe. NPT threads require sealant period!

And I never said you can't use copper or plastic lines or that they don't work, I said it's safer to run braided stainless line for this and many others here believe the same. Don't pretend to school me here.

65 Chevelle 2Dr. Post,Global West stage 3, Small Block, Small Journal 337cid. Howards roller cam .570/.570" lift 227/233 duration @ .050 LS112, Speed Pro forged pistons 10 to 1, Trick Flow 195,23 degree heads, Holly 750 Ultra, Edelbrock Performer RPM air gap.

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post #9 of 13 (permalink) Old Oct 7th, 15, 10:07 PM
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Re: Oil pressure sending unit leak, 383 stroker

NPT threads do not require sealant, it is a tapered thread. What I'm saying is he tried everything to seal a leak that may not be a leak. The leak may be coming from the compression side of the fitting which is usually the problem. Replace the fitting with a new one.

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post #10 of 13 (permalink) Old Oct 7th, 15, 10:54 PM
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Re: Oil pressure sending unit leak, 383 stroker

NPT fittings definitely do need sealant.
The best thing I've found to use on pipe threads when used for automotive applications to seal antifreeze, oil or gasoline is Permatex #2 form-a-gasket sealant.

Also a little pipe dope on compression ferrules is very helpful. The main thing with those is just don't over tighten compression nuts.

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post #11 of 13 (permalink) Old Oct 8th, 15, 1:18 AM
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Re: Oil pressure sending unit leak, 383 stroker

Any pipe fitter will tell you to use pipe dope/sealant on NPT fittings.

If you should decide to upgrade... http://www.jegs.com/i/Russell/799/64...47#moreDetails
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post #12 of 13 (permalink) Old Oct 8th, 15, 10:34 AM
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Re: Oil pressure sending unit leak, 383 stroker

Unbelievable it really is. I try to help people then my work get sabotaged on a daily basis. It's getting old man, really old.

65 Chevelle 2Dr. Post,Global West stage 3, Small Block, Small Journal 337cid. Howards roller cam .570/.570" lift 227/233 duration @ .050 LS112, Speed Pro forged pistons 10 to 1, Trick Flow 195,23 degree heads, Holly 750 Ultra, Edelbrock Performer RPM air gap.

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post #13 of 13 (permalink) Old Oct 8th, 15, 8:58 PM
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Re: Oil pressure sending unit leak, 383 stroker

I use a grease gun hose for oil pressure lines. Probably over kill but they will definitely stand the pressure and abrasion. The only down side is the size of hole needed in firewall. Grinding the flats round lets you use a smaller hole. #2 Permatex for sealer.
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