Yanmar pt thread

[oldsaltyfish]

I am installing a water temperature gauge in my Yanmar 3jh. The VDO sender has a 3/8 18 NPT thread and the thread in the Yanmar is a 3/8 18 PT thread. When I went to install it, it would on screw in 1 turn by hand. I contacted the instrument shop where the sender was purchased and they suggested to keep screwing it in with a spanner and expect some resistance as it is a taper thread. I am a bit loath to do this as it just feels like it is too tight. Some research suggests that these two threads are not the same but a NPT tap could be run down the PT hole without drilling. Hmm not sure about this? Any ideas for a fix? VDO don't seem to make senders with a PT thread. Any advice would be appreciated.

 

[savageseadog]

Are you sure the thread on the Yanmar isn't BSP?

 

[oldsaltyfish]

No not sure as the information is a bit confusing. Yanmar temperature switch has 3/8 18 PT thread according to parts information. Was also told that PT threads are " a metric thread form in imperial sizes" really confused now. So the PT 3/8 may well be the same as BSP, or not??

 

[RichardS]

I am installing a water temperature gauge in my Yanmar 3jh. The VDO sender has a 3/8 18 NPT thread and the thread in the Yanmar is a 3/8 18 PT thread. When I went to install it, it would on screw in 1 turn by hand. I contacted the instrument shop where the sender was purchased and they suggested to keep screwing it in with a spanner and expect some resistance as it is a taper thread. I am a bit loath to do this as it just feels like it is too tight. Some research suggests that these two threads are not the same but a NPT tap could be run down the PT hole without drilling. Hmm not sure about this? Any ideas for a fix? VDO don't seem to make senders with a PT thread. Any advice would be appreciated.

I don't know what the thread is but I know that taper threads normally screw in more than one turn before tighening up so I think that tightening with a spanner will just strip that first thread.

Richard

 

[savageseadog]

I'd just find or buy a 3/8 BSP fitting of some sort and try it for size. Marine Power in Bursledon will probably know. I'd echo the point about not forcing the situation, taper threads will normally turn easily for a turn or two so what you have can't be right.

 

[Latestarter1]

I'd just find or buy a 3/8 BSP fitting of some sort and try it for size. Marine Power in Bursledon will probably know. I'd echo the point about not forcing the situation, taper threads will normally turn easily for a turn or two so what you have can't be right.

Simply incorrect. BSPT (British Standard Pipe Taper) is similar thread form to NPT U.S National Pipe Taper) however 3/8 NPT is 18 TPI whereas 3/8 BSPT is 19 TPI.

There is no such beast as a PT thread, clue was in the original post giving TPI as 18.

Yanmar in line with majority of engine manufacturers who sell into U.S use NPT threads for sensor fittings. BSP is the the oddball.