A very quick couple of questions which will hopefully save me some time,if you don't mind please. I need the thread size for the oil pressure sender on my 1994 3.2s. If anyone has a link to this kind of info it would also be very much appreciated. I have a little sideline project underway on my 40 and this will help speed up the process.Thanks in advance.

 

Hi twack,

According to my records, on our '93 4.0L the oil pressure sender thread was 1/2 inch-20 threads per inch (it was not metric). Your 3.2L uses the same oil pressure sender so the threads should be the same.

EDIT: I was wrong - I should have written down 1/2 inch-27 threads per inch. See the ensuing posts in this thread.

Cheers,

Don

 

 

Hi Vee,

I'm glad we agree that the thread is not metric, but now you've got me wondering if I wrote down 1/2-20 but should have written down 1/2-27 (fine thread). You mention 1/8-27 so I assume you mean an NPT tapered pipe thread. I think I recall that the threads on the sender are parallel, not tapered, but I could be wrong. It's hard to tell in the photo below of my old sender and the bolt I used to plug the port:



On NPT, the threads are noticeably tapered, so I'm not sure:



On our '93, the 1/2-20 or 1/2-27 bolt threaded in all the way and sealed the port.

Now I will be really curious to know which thread twack discovers his sender uses!

Cheers,

Don

 

Here's a pic of the two "alternate" units ..threads are not tapered.

 

 

Thank you all for the input,gratefully appreciated. I think I've worked out the way forward but as things don't always go as planned I will do so cautiously. As it turns out I will be dealing with BSP and NPT. I'm assuming the thread in the block is BSP and the hardware I'll be running from it will be NPT so I'll need a 1/2" BSP to 1/8" NPT adapter,which are readily available...I also have a plumber friend who might be able to furnish me with some other bits and bobs that might come in handy. I'll let you know how I get on. Thank again.

 

 

I think we've collectively produced enough information for a definitive answer. Note the sealing copper washers on the new senders in Larry's photos. One can also be seen on the old sender in my photo. Sealing washers are used on fasteners with parallel threads, like oil drain plugs. If the sender used a tapered pipe thread, it would rely on thread sealant or Teflon tape and the wedge action of the tapered thread for a leak-free seal. But the oil pressure sender is a single-wire unit whose ground path is through the block and engine ground strap. Thread sealant or Teflon tape would interrupt the ground path and the sender would not work. This is why oil on the sender threads causes the dash gauge to be inoperative. So the sender threads must be parallel, and the sealing washer is critical because no sealant or tape can be used on the threads.

My vote is that the sender threads are 1/2 inch, 27 threads-per-inch, standard "fine pitch" parallel screw threads.

Cheers,

Don

 

Vee, would that be the same for a 95 XJS 4.0 ? ( 1/8 x 27)

 

Yes. But don’t take my word for it. Cross reference your part number with a 1996. If it’s the same part, it’s the same thread.

 

Thank you.

 

G Man,

Note that our conclusion from this discussion is that the sender threads are not tapered pipe threads (1/8X27) but are instead parallel 1/2 inch fine thread (27 threads per inch). See the photos in posts #4 and #5 showing the sender threads.

Tapered pipe threads require Teflon tape or thread sealant, but either would interfere with the ground path for the sender, which is through the engine block and ground strap. This also means that you want to clean as much oil as possible from the threads of the sender port before installing the new sender.

If you're just looking to plug the port, a short 1/2-27 bolt should do the trick, and you can use thread sealant or Teflon tape and replace your sender with an appropriate resistor connected to ground.

Cheers,

Don