Temperature gauge knowledge deficit

[K10-Kansas]

Hi all. My new gauge cluster has electric posts for the temperature sensor and the engine has a water line running to a crap add-on gauge that is going in the trash as soon as I can make sense of what needs to be done.

Do I buy a sending unit and screw it into the spot where the old line is?

[Accelo]

Yup, that's exactly what you do.
The Holley gauge has a 3/8 NPT. (national pipe thread)
Difficult to tell from your picture but yours could be 1/2" NPT.
I would confirm the pipe size before ordering. I dislike the look when adapters are used.
Did the new cluster come with any specifications for the sensor?
Be forewarned the actual resistance, at 180 deg F, can vary a lot between sensors.

From the website.
Holley coolant temperature sensors are designed to work with Holley's Pro-Jection fuel injection systems. They are available for both digital and analog systems and feature a Weatherpack connection that will easily plug into your Pro-Jection wiring harness.
At this time there is no ohms rating directly listed.

Geeze, please help me but don't provide and facts. Seems to be the wave of the future.
Caveat emptor.
Cheers

[dmjlambert]

The sending unit you have pictured is not the one for a stock temperature gauge.
Here is the correct one.
https://www.amazon.com/gp/product/B000C9SM22/

Others have purchased a good one from Lectric Limited, and the size and shape is exactly the same as the one I picture from Amazon.

There is no 3/8" NPT sender that works with the gauge, and you can only use the 1/2" NPT sender with stock gauges.

If you want to put it in a 3/8" NPT hole you need to have it turned down and re-threaded by a machinist. Forum member A1971Blazer turned mine and threaded it, and others have reported forum member brian mac does the work, too.

You instrument cluster looks like a stock one, but Accelo asks a good question, does the temperature gauge on that cluster come with an specifications or is it sold as a direct replacement for stock? Or is it a restored stock cluster?

[dmjlambert]

Here is a thread with additional information.

https://67-72chevytrucks.com/vboard/...d.php?t=790164

[K10-Kansas]

Originally Posted by dmjlambert

The sending unit you have pictured is not the one for a stock temperature gauge.
Here is the correct one.
https://www.amazon.com/gp/product/B000C9SM22/

Others have purchased a good one from Lectric Limited, and the size and shape is exactly the same as the one I picture from Amazon.

There is no 3/8" NPT sender that works with the gauge, and you can only use the 1/2" NPT sender with stock gauges.

If you want to put it in a 3/8" NPT hole you need to have it turned down and re-threaded by a machinist. Forum member A1971Blazer turned mine and threaded it, and others have reported forum member brian mac does the work, too.

You instrument cluster looks like a stock one, but Accelo asks a good question, does the temperature gauge on that cluster come with an specifications or is it sold as a direct replacement for stock? Or is it a restored stock cluster?

Thanks, the cluster is a direct replacement for stock. The adapter looks to have an 11/16th thread diameter and 18 pitch on the threads. The sending unit that 2as in the adapter looks to have a 5/8th diameter and 20 thread pitch. Thanks for your help on this. I looked for size and pitch on the unit you linked to on Amazon but don't see that info. Do you happen to know if it fits my engine or maybe fits my adapter?

[dmjlambert]

The large hole is probably 1/2" NPT and the adapter is probably adapting to 3/8" NPT. NPT fittings are weird and have quite different actual sizes.

I'm not sure what you have, but here is a web page with a chart.
https://help.summitracing.com/app/an...npt-fitting%3F

The sender on the Amazon site that I gave the link for fits 1/2" NPT. The threads on all these fittings is actually technically called NPTF but known colloquially as NPT national pipe taper thread sizes.

In any case, you'll need to buy the sender that has 1/2" NPT and then if it doesn't fit you'll need to have it turned and threaded by a machinist, because there is no sender for our trucks that works with a stock gauge and available in a different thread size.

[dmjlambert]

Here is another thread I had bookmarked for good info about these senders.
http://67-72chevytrucks.com/vboard/s...d.php?t=779140

[chiefcfd]

Another thing, you are going to need to find the stock wire if it is still there. If not you will need to run a new wire to the stock plug if you are using the stock plug. It doesn't wire to the gage itself. It runs thru the printed circuit.

[K10-Kansas]

Originally Posted by dmjlambert

The large hole is probably 1/2" NPT and the adapter is probably adapting to 3/8" NPT. NPT fittings are weird and have quite different actual sizes.

I'm not sure what you have, but here is a web page with a chart.
https://help.summitracing.com/app/an...npt-fitting%3F

The sender on the Amazon site that I gave the link for fits 1/2" NPT. The threads on all these fittings is actually technically called NPTF but known colloquially as NPT national pipe taper thread sizes.

In any case, you'll need to buy the sender that has 1/2" NPT and then if it doesn't fit you'll need to have it turned and threaded by a machinist, because there is no sender for our trucks that works with a stock gauge and available in a different thread size.

Thanks for this. I took a screenshot of the chart on that page and will remeasure and check my notes. I appreciate it.

[K10-Kansas]

Originally Posted by chiefcfd

Another thing, you are going to need to find the stock wire if it is still there. If not you will need to run a new wire to the stock plug if you are using the stock plug. It doesn't wire to the gage itself. It runs thru the printed circuit.

Thanks. I'm in the middle of running the American Auto Wire Classic Update complete wiring harness to direct replacement for OEM dash cluster. I'm learning a lot today.

[K10-Kansas]

Originally Posted by dmjlambert

Here is another thread I had bookmarked for good info about these senders.
http://67-72chevytrucks.com/vboard/s...d.php?t=779140

Thanks, I went ahead and sent A1971Blazer a message.

I'm really confused by that NTP chart.

My engine has approximately a 3/4 inch standard female port. The 1/2 NTP is 25/32 female standard so maybe I don't need it machined to 3/8 NTP because 3/8 NTP is 5/8 standard female?

[Getter-Done]

Here is another article on NPT.
Hope this helps.
Link: https://www.pegasusautoracing.com/do...%203%2F8%20NPT.

Ordering and using NPT fittings can be confusing because the nominal sizes have no relation to thread size. To make matters worse, NPT fittings do not fit together the way most other fittings do. This has led many people to believe that they have mismatched sizes. Fortunately, NPT sizes are easy to identify. The sizes are also different enough that it is impossible to even start to assemble two different sizes together.


(Background)
NPT stands for National Pipe Tapered thread. It is also sometimes called National Pipe Thread, NPTF (F for Fuel), American Standard Taper, or simply "pipe". Most other plumbing fittings have straight or parallel threads, but NPT fittings have a tapered thread profile. The outside diameter of the male thread tapers down from the base, so the end of the fitting has a smaller OD than the base of the fitting. The matching female thread has a larger OD at the opening, tapering down as it goes in.

NPT fitting sizes refer to the nominal ID of a standard cast-iron pipe. This is where the confusion comes in. Most plumbing fittings are named for the thread size, but NPT sizes are not. An NPT fitting measuring 3/8" OD thread is actually a 1/8 NPT, not 3/8 NPT. Use the chart below to positively identify NPT fitting sizes.

[K10-Kansas]

Thanks Getter-Done. That explains why I'm totally confused on the sizes.

I went ahead and ordered this one https://www.lectriclimited.com/tempe...ng-unit-117353

Since my female port on the engine is 3/4 inch standard, do you think the unit I bought will still need to be machined?

[Getter-Done]

Originally Posted by K10-Kansas

Thanks Getter-Done. That explains why I'm totally confused on the sizes.

I went ahead and ordered this one https://www.lectriclimited.com/tempe...ng-unit-117353

Since my female port on the engine is 3/4 inch standard, do you think the unit I bought will still need to be machined?

If the female threads in your head are truly 3/4" NPT.
Sounds like you will need a 3/4" to 1/2 " reducer bushing.

As Accelo had mentioned above,
I am not a big fan of reducing bushing or adapters.
It's just one more place to have a leak in my eyes.

Sometimes that is the way to go though because of all the changes over the years that happen to these trucks.

I have pipe fittings in a big box in the shop.
I still have to go and double check on some sizes of this NPT stuff.

[dmjlambert]

On this topic confusion is OK. If you had complete understanding about NPT sizes, that's when we would have to worry about you. :-) If the hole in the engine or the threads screwing into it is about 3/4" as measured with a ruler or caliper, then that sensor is probably going to fit fine.

[K10-Kansas]

Originally Posted by dmjlambert

On this topic confusion is OK. If you had complete understanding about NPT sizes, that's when we would have to worry about you. :-) If the hole in the engine or the threads screwing into it is about 3/4" as measured with a ruler or caliper, then that sensor is probably going to fit fine.

Great thanks. I'll cross my fingers for something working easy.

[chiefcfd]

I ordered and received a turned down sending unit from A1971Blazer this week. My Vortec head has the 3/8 thread hole in it. I have been running a bushing but wanted to clean it a up a bit. I'm sure it will read more accurate.

[K10-Kansas]

Originally Posted by chiefcfd

I ordered and received a turned down sending unit from A1971Blazer this week. My Vortec head has the 3/8 thread hole in it. I have been running a bushing but wanted to clean it a up a bit. I'm sure it will read more accurate.

I got a sending unit from A1971Blazer. Great price, fast shipping and it fit perfect.