Thread size thread

[NavajoAficionad]

With luck someone will have an answer for this question regarding the thread size for a temperature sending unit.
This is for a 92 Navajo v6.
I bought this truck and found a small leak coming from the temperature sending unit, the single wire type going to the gauge. When I removed it I found the threads were cross threaded for about two turns. Thus it had a good reason to be leaking.
I got a new sending unit but still have to clean up the threads. On measuring the sending unit it measures .660" which suggests it could be a tight 17x1.5mm thread or a loose 11/16-16 thread. It is too tight in that area to physically check the hole on the manifold.
Can anyone tell me if this is 11/16 or 17mm or maybe some pipe thread? the 17mm seems to be the right size but with 11/16 being more common I thought I should ask before buying an expensive tap.
Thanks for any assistance!

 

[matt0248]

It is probably a NPT (national pipe thread) size. Take it to a dardware store and see if it matches up better. They may even have a NPT gauge to check the threads of the new one. pipe threads are tapered, not straight like regular SAE or metric threads. They do make NPT taps to clean out the threads too.

 

[NavajoAficionad]

It could be a 3/8 pipe thread of course. I did try calling the hardware stores around here but so far no one even carries pipe taps. Standard sized are there though. Thus I asked here because I will have to order on line and they can't help on determining what is right.
If anyone knows for sure I still need advice.

 

[matt0248]

It could be a 3/8 pipe thread of course. I did try calling the hardware stores around here but so far no one even carries pipe taps. Standard sized are there though. Thus I asked here because I will have to order on line and they can't help on determining what is right.
If anyone knows for sure I still need advice.

Go to home depot with the new sending unit and see if it threads into a 3/8 NPT brass fitting. that will confirm it, then order the tap.

 

[Maniak]

I looked up the sending unit on rockauto to get the right part # for the single wire sending unit (the one for the gauge).

I came up with Standard Products # TS58. I then looked up standard product ts58 thread using google and everything I find says its 3/8 - 18 NPT.

btw.. Ace Hardware does carry that tap (at least the ones around here). Its not exactly cheap from them, but they have it.

~Mark

 

[NavajoAficionad]

I looked up the sending unit on rockauto to get the right part # for the single wire sending unit (the one for the gauge).

I came up with Standard Products # TS58. I then looked up standard product ts58 thread using google and everything I find says its 3/8 - 18 NPT.

btw.. Ace Hardware does carry that tap (at least the ones around here). Its not exactly cheap from them, but they have it.

~Mark

That is VERY helpful. Unfortunately Ace was the first place I tried. They carry nothing in pipe taps or even odd standard taps. Of course with the plumbing I have seen around here I doubt there are any plumbers in the area so there is no need for something as basic as a tap...but that is another story.
I did not think to try to cross reference the part number and I thank you for your help. Thus I am off to order a tap.

 

[scdix50]

After you get the threads dressed, wrap the threads on the sensor with plumbers tape. It will help seal around the damaged threads.

 

[rickybobby]

After you get the threads dressed, wrap the threads on the sensor with plumbers tape. It will help seal around the damaged threads.

plumbers tape will make the readings inaccurate, because the signal grounds through the treads

 

[NavajoAficionad]

plumbers tape will make the readings inaccurate, because the signal grounds through the treads

I've done that before and can get away with it. Since the damaged threads are at the top of the manifold I can wrap the threads of the sensor only at the top and the bottom threads will ground. I have also gotten away with slightly over tightening the sensor if it mounts on cast iron and the the threads will cut though the tape and ground but stay in place for sealing purposes. I can not do that this time because it is an aluminum manifold.
I will probably partially tape it this time. Two threads are not a lot but it can make a difference.

 

[NavajoAficionad]

Thread wars. The final chapter.

As a final followup on this thread It was a 3/8-18 pipe tap. Once I had the tap in hand it was a 5 minute job to clean and straighten the threads and another 5 to install the sending unit. I did cut the threads about 1/2 turn deeper just to give it a fresh surface on the threads.
As an experiment I first installed the sending unit without teflon tape and it did not leak. The fresh surface let the threads seal properly. I then installed it with teflon tape on half of the threads to make sure I still got a good ground and it was fine. Thus tape is an option if someone else needs to seal a leak in the threads.
No I have to move on to a dozen other nit picking jobs that are not needed but are desirable. Thanks for the help folks!!!!