Oil pressure sending unit leaking

[chaseincats]

Was trying to track down a leak and I think I've narrowed it down to oil sneaking out of the threads of the oil pressure sending unit.  The unit works great outside of the small leak.  Is there an o-ring between it and the block that has gone bad or do they seal to the block in a different way?

[SteveJ]

The threads are either BSPP or BSPT. I'm not sure which. The FSM says to use conductive sealant, but I have no idea what that is, and Google hasn't been my friend in my efforts to see what it might be.

[DatsunZGuy]

It has been years since I had to swap an oil pressure sending unit out and I don't recall an o-ring.  I say just get some high temp thread sealant and give it a try.  It is the cheapest and least invasive first step in the process.

[dutchzcarguy]

4 hours ago, chaseincats said:

Was trying to track down a leak and I think I've narrowed it down to oil sneaking out of the threads of the oil pressure sending unit.

I think you have the same sensor there as the 280zx.. the one with those 2 contacts? They tend to leak right through the sensor and oil comes out on the contact-side! When they do this they are also prone to giving a lower pressure on your meter..  best to put a new one in..

[dutchzcarguy]

4 hours ago, chaseincats said:

do they seal to the block in a different way?

For as far i know the threads are conical (Tapered) just a drop of loctite is good enough.  (And yes, the connection has to be electric conductive as the sensor makes some "earth" to the meter to make it come of the zero .. 😉  )

[Racer X]

10 hours ago, chaseincats said:

Was trying to track down a leak and I think I've narrowed it down to oil sneaking out of the threads of the oil pressure sending unit.  The unit works great outside of the small leak.  Is there an o-ring between it and the block that has gone bad or do they seal to the block in a different way?

The oil pressure tap on the engine block is a tapered pipe thread, originally JSP if memory serves me. It is very close to 1/8” pipe thread, and a 1/8” pipe fitting will work.

Pipe threads seal by slight deformation of the threads as the fittings are tightened, so additional sealant is more insurance against a leak.

Some Teflon thread paste will do, or you can use a hydraulic thread sealant such as LocTite 542. I’ve used it for years with no leaks, and there is still enough metal to metal contact to allow the sending unit to ground.

Take the sending unit out, clean the threads on it, and the block. Examine the threads on both to ensure there is no damage or cracks, apply a few drops to the threads and assemble.

Don’t overtighten, just snug enough to keep it from leaking.

 

 

 

 

[240zadmire]

19 hours ago, SteveJ said:

The threads are either BSPP or BSPT. I'm not sure which. The FSM says to use conductive sealant, but I have no idea what that is, and Google hasn't been my friend in my efforts to see what it might be.

it's 1/8 BSPT threading. 

[chaseincats]

11 hours ago, Racer X said:

The oil pressure tap on the engine block is a tapered pipe thread, originally JSP if memory serves me. It is very close to 1/8” pipe thread, and a 1/8” pipe fitting will work.

Pipe threads seal by slight deformation of the threads as the fittings are tightened, so additional sealant is more insurance against a leak.

Some Teflon thread paste will do, or you can use a hydraulic thread sealant such as LocTite 542. I’ve used it for years with no leaks, and there is still enough metal to metal contact to allow the sending unit to ground.

Take the sending unit out, clean the threads on it, and the block. Examine the threads on both to ensure there is no damage or cracks, apply a few drops to the threads and assemble.

Don’t overtighten, just snug enough to keep it from leaking.

 

 

 

 

Thanks I'll give this a shot.  I have teflon tape laying around so that should do it then.

[240zadmire]

Isn’t the Teflon tape insulate the sending unit’s ground connection? 

[dutchzcarguy]

5 hours ago, 240zadmire said:

Isn’t the Teflon tape insulate the sending unit’s ground connection? 

Yes, if you put up more than let's say 1,5 rounds.. so just use a little not 3-5 rounds because that will isolate your sensor from ground. better use a drop of liquid loc-tite. You can use teflon (PTFE) tape but if the meter does not give any oilpressure you know you used to much tape 😉 !!

[Racer X]

8 hours ago, 240zadmire said:

Isn’t the Teflon tape insulate the sending unit’s ground connection? 

That’s why I suggested the LocTite 542. A drop or two of an anerobic thread sealant  will seal without interfering with the electric ground path.

[Racer X]

11 hours ago, chaseincats said:

Thanks I'll give this a shot.  I have teflon tape laying around so that should do it then.

It is possible that the Teflon tape will insulate the sending unit from the engine, blocking the path to ground.

Most auto parts stores carry small vials of an assortment of thread locking and thread sealing anerobic compounds for a couple of bucks.