Installing NPT adapters without hex flats
Posted by jedigreg1984@reddit | projectcar | View on Reddit | 19 comments
Needing a quick sanity check here. Would like to use these supplied NPT thread adapters without hex flats to install 1/8" NPT gauge senders into 1/4" and 3/8" NPT threaded locations on an FE Ford. Obviously I have to install the sender to the adapter first, but how can I avoid overtorquing the smaller thread and undertorquing the larger one? Am I overthinking this?
I have a couple of appropriate thread sealers/lockers if that might help, but I normally don't use them with NPT and have not had issues with stock-style senders.
I also have plenty of NPT adapters *with* the hex on them, but using them mounts the sender tip too high (out of the coolant flow or shrouded from it). Does that really affect the temperature measurement? Thanks all
Deep-Hovercraft-6863@reddit
Maaaaan, please consider using a sensor that doesn’t require an adapter if you can. Every project I’ve done with NPT adapters leaks or sweats at some point. Every time I’ve replaced the part with one that fits sans adapter.
jedigreg1984@reddit (OP)
Yeahhh i hear ya. It takes a lot for me to post here, but this one didn't pass the smell test and your experience is exactly why
I can look up some options that match the resistance ranges of the gauges (DigiKey might have something) but it's just more time and money to get it right. Doing oil pressure, oil temp, and coolant temp and there's already going to be an elbow and tee fitting for the oil stuff so...i think I'm going to just send it reasonably firmly with the blue Permatex and move on
zkulka@reddit
I apologize that this will sound like criticism. But “more time and money to get it right” is the difference between a reliable car and one that frustrates you. I don’t know the back story here, you may have a perfectly reasonable need get this rig rolling in a hurry. But in the long run, patience and investing in the right parts for the job became an asset for keeping my classics reliable as daily commuters.
jedigreg1984@reddit (OP)
Mocked it up with everything clean and ready to go, and it didn't feel right to my hand. The thread sizes and tightness required to seal were too bi of a mismatch. Correct sized sensor finally located and in the mail
jedigreg1984@reddit (OP)
No offense taken, and you're not wrong. I make this calculation often and usually, almost always, choose to spend the money and time with good results. In this instance however I'm pretty sure it's not necessary and that I'm really overthinking this. Time will tell and that's a risk I'm comfortable with right now
jedigreg1984@reddit (OP)
Mocked it up and it didn't feel right to my hand. Correct sized sensor in the mail.
Cartman300@reddit
Is this used for high temp? If not, brass adapters can be soldered.
jedigreg1984@reddit (OP)
You know what, i didn't even think of that. I have a regular ol solder gun for electrical stuff, not sure if that's exactly what you mean
Highest temp would be mild performance automotive oil so figure 250-275F max on its toughest day
Cartman300@reddit
Could work just fine if that's within the range of the temp sender, else you would have to do it quickly.
Just make sure your coolant doesn't reach a temp that will melt the solder.
jedigreg1984@reddit (OP)
I do have a torch but haven't ever done this - sounds extremely cool and convenient, I should learn
For now I think I'll take my chances with careful tightening and thread sealer/locker. But thank you for suggesting it!
greycar@reddit
I wouldn't expect mounting then slightly out of the coolant flow to chase problems. If it was an airstream maybe I'd feel differently but water transfers heat so well.
My reco is to use the hex sided ones that you have.
jedigreg1984@reddit (OP)
Will consider! Seems like the coolant would get to the sensor no matter what, but it just looks wrong/bad
humandalek42@reddit
I’m curious of the real answer myself too. My initial thought would be to install the adapter first with an npt threaded item or tap with a stopper(nut?) of some sort behind the adapter to create like a double nut sorta situation. Then install the desired npt thingy
SirRonaldBiscuit@reddit
This is what I would do
jedigreg1984@reddit (OP)
That sounds nice but there's no such tool obviously. I don't see any way to get the adapter in the intake first short of machining holes or slots for a spanner style wrench. Ain't nobody got time for that. Also I'd like for the adapter to come out at some point if necessary, especially if it's left behind if the sender comes out on its own... But whatever.
My thought is that you get the adapter onto the sender as tight as possible by hand (1/8" NPT doesn't need that much torque to seal), and then screw the whole thing into the intake - and everything tightens against each other enough because the sender and intake port are both putting pressure on the adapter from inside and outside
I like to get the torque right whenever possible. Sometimes it's not realistic though and you just have to trust. I just want the sender to read properly too and not make an air pocket
RunV5@reddit
I would thread the adapter to the sensor, by hand, bottom it out, then thread it in as one
Klo187@reddit
Get a bolt/fitting that matches the internal thread and has a shoulder, and stack a copper washer under it. Run it into the hole and tension to the spec of the larger thread. The copper washer should stop the internal threads from over torquing. Because the torque is being transferred through the top of the fitting and the clamping surface between the copper washer and bolt, it shouldn’t put any actual tension on the threads. You should be able to remove the fitting/bolt without loosening the larger fitting.
turbo_charged@reddit
I would turn the sensor and adapter you are holding into an assembly, fusing them together somehow.
Make those two parts fused together so you can remove the entire thing together using the threads of the sensor.
If you’re concerned about your thread sealant affecting the sensor readout, I would add a ground wire to the body of the sensor and run it directly to the ground connection of your gauge. This ensures the sensor and the gauge are both using the same ground path, increasing accuracy.
jedigreg1984@reddit (OP)
I can try to get the adapter onto the sensor with a soft jaw vise, sure. That would get the bigger NPT threads tighter before the smaller ones want to move more. The ground wire thing would work but in my experience it's not an issue even with contaminated threads - more worried about leaks and looseness over time with heat cycles