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Oil Sending Unit Leak/Spray

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?
 
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.
 
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.

Did you not read his post? It’s visually coming from the sending unit to extension joint.
 
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.
 
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.
 
How tight is the seal when dry fitting? Could be the threads are incorrect in one or the other. Chinese parts?
 
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.
 
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.
 
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.

I was just getting ready to type that same thing.

No, really!
 
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.

It is possible that the extension, internal threads got buggered up at sometime.
 
You could always hook up a mechanical gauge and see if that leaks. Buy an elcheapo.
 
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.
 
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.
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.
 
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.
 
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.

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