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Oil Sending Unit Leak/Spray

Discussion in 'Engine and Drivetrain/Mechanical' started by Patrick Stapler, Jan 21, 2018.

  1. Patrick Stapler

    Patrick Stapler Active Member

    I have a stock oil sending unit setup on my 289 that is spraying oil at cruise RPM...essentially 2500RPM and above. Here is what I have tried, two OEM steel extensions from the block and three new OEM style (one NOS) sending units. I have tried multiple sealing types as listed below with these parts. Using a high volume Melling oil pump. Oil pressure is around 60psi.

    I laid under the car while my son held the engine at 3000RPM. I could see the oil spray up onto the bottom surface of the sending unit and onto surrounding surfaces. The oil is not coming out of extension/block connection. My next two tests are Permatex Black RTV and then just plugging the extension to test if it's the extensions or the sending units.

    As supplied out of the box teflon tape on new unit
    Taped with teflon tape
    ARP teflon based thread sealant paste
    Loctite thread sealant
    Teflon tape and Loctite thread sealant
    Permatex Aviation Form-A-Gasket

    All leaked and still leaking.

    Any ideas?
     
  2. Boom

    Boom Active Member

    So its leaking from the block? Is the area clean? Check to make sure there are no cracks. Maybe run a tap through the hole to clean the threads up and then put the extension on with fresh teflon tape/paste. Make sure also that the extensions aren't blocked/clogged. Shouldn't cause it to leak, but still a good thing to check while you're there.
     
  3. Patrick Stapler

    Patrick Stapler Active Member

    "The oil is not coming out of extension/block connection."
     
  4. msell66

    msell66 Burning Fossil Fuels Donator

    Did you not read his post? It’s visually coming from the sending unit to extension joint.
     
  5. Boom

    Boom Active Member

    So it's coming out of the bottom of the sending unit itself? My bad, I misread what you said. Thought you said it wasn't coming out of the extension at all.

    You might have to get a special sending unit, maybe the stock ones are only good a lower pressure. I have whatever sending unit AUtometer uses, but I don't have that high of pressure normally, only like 45 ish.
     
  6. Patrick Stapler

    Patrick Stapler Active Member

    No worries. I have wondered if high pressure sending units are available. However, this is visibly spraying from the threads at the sender/extension connection...again two different extensions and three different sending units. Unless I am completely screwing the pooch installing all...which is possible.
     
  7. msell66

    msell66 Burning Fossil Fuels Donator

    How tight is the seal when dry fitting? Could be the threads are incorrect in one or the other. Chinese parts?
     
  8. Boom

    Boom Active Member

    Might be worth getting a brass extension, swear I've seen em. That and a thin layer of teflon tape. Should seal up and the brass will have some "give" that might make for a better seal then the steel extension. Just a crazy thought.
     
    msell66 likes this.
  9. Patrick Stapler

    Patrick Stapler Active Member

    Pretty sure at least two of the sending units are offshore as they are aftermarket. One from local parts store, one from NPD. However, I believe one to be NOS as I have owned it for over 30 years and was in a Motorcraft box...many years ago.
     
  10. msell66

    msell66 Burning Fossil Fuels Donator

    I was just getting ready to type that same thing.

    No, really!
     
    Boom likes this.
  11. Patrick Stapler

    Patrick Stapler Active Member

    I'll add it to the list of test...as they fail. Hell I might even design and machine my own.
     
  12. msell66

    msell66 Burning Fossil Fuels Donator

    It is possible that the extension, internal threads got buggered up at sometime.
     
  13. Patrick Stapler

    Patrick Stapler Active Member

    I'm down with that, but on two...and all the different sealing techniques? I mean with the Permatex it's basically glued in...right?
     
  14. msell66

    msell66 Burning Fossil Fuels Donator

    You could always hook up a mechanical gauge and see if that leaks. Buy an elcheapo.
     
  15. Patrick Stapler

    Patrick Stapler Active Member

    I did...when I broke in the engine. I had brass fittings connected to the original extension to the car and then to a mechanical oil pressure gauge. No leaks.
     
  16. 3175375

    3175375 Well-Known Member

    Is the extension brass? I wrestled with some brass fittings for my water heater that were made in China. Replaced them with USA made parts. Done.
    You also may want to silver solder the connection.
     
  17. Horseplay

    Horseplay Well-Known Member

    This one is not that tough. You've simply got poorly machined threading on something(s). I highly doubt the issue would be with the steel extension but it is possible. Much more likely the actual sending unit threads. Visit an Ace hardware and get a 4" long 1/4" NPT nipple. Get a 1/4" to 1/8" fitting as well. Use teflon tape on the threads and put it all together. Tape is better than the other stuff, IMHO, for this one. The tape acts as a very thin filler, if you will. As mentioned earlier, brass is typically tighter fit which can help overcome some thread issues.
    You don't need a "high pressure" sending unit (I don't even think there is such). It's leaking at the threaded connection per your explanation and that has nothing to do with the actual sending unit itself other than the threaded stem by which it mounts.
     
  18. Patrick Stapler

    Patrick Stapler Active Member

    Removed, cleaned, and reinstalled Ford sending unit with black RTV. All threads inspected thoroughly. Nothing appeared to be inconsistent. Will test in a few days. If this doesn't work, I have a plug to install just to test the extension. However, it didn't leak when I broke in the engine with the external gauge attached.

    [​IMG]

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    [​IMG]
     
  19. msell66

    msell66 Burning Fossil Fuels Donator

    Did you check the block?



    I kill myself.
     
  20. Patrick Stapler

    Patrick Stapler Active Member

    THE DAMN BLOCK IS NOT LEAKING...
     
    msell66 likes this.

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