Coolant temp gauge

[Magicnbomber90]

Hey how’s it going again I’d appreciate the help with getting my coolant temp gauge to work on my cluster . I have a 350 from a 70s vehicle with the HEI distributor on it and the coolant temp sensor isnt hooked up. I was wondering if I can tuna a wire from the sensor to the gauge and be ok or does it have to go anywhere else befor the gauge. I’ve attached images of the type of coolant temp sensor it has .
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[Captainfab]

Assuming you have an actual gauge in your dash, that is the correct style of temp sender. However you will need the sender specific to your year of truck. as for the wiring, the factory dark green wire ran thru the firewall, into the harness under the dash and made it's way to the gauge panel. I believe the dark green temp sender wire should be in the loom on the drivers side fender that also goes to the alternator and voltage regulator.

[Magicnbomber90]

It’s the oem gauge just not the oem engine that’s what I’m worried about I see a green wire on the loom that’s leading to the alternator it’s just not connected to anything is there a sending unit I can buy?
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[ray_mcavoy]

The correct sending unit for use with the original temperature gauge was GM #1513321. Lectric Limited makes an accurate reproduction.

As Captainfab said, the original temperature sending unit wire was dark green. However, instead of being in the loom with the alternator wiring, it was in the engine harness with the starter & coil wiring. That harness has a 6-cavity plug where it goes through the firewall up above the engine over toward the passenger side.

The temp sender wire originally ran along side the coil wiring in that loom and then branched off on it's own near the coil. From there it ran through a section of asphalt coated fabric loom clipped to the side of the valve cover. On inline-6 engines the sending unit was originally located in the lower thermostat housing and on V8 engines it was originally in the intake manifold just off to the driver side of the thermostat housing.

1968 & newer small block Chevys had the temp sender located in the cylinder head between the #1 & #3 spark plugs so you might have to extend / re-route the wire a bit. Although some intake manifolds (especially aftermarket ones) still have a port up near the thermostat. Just be aware that the #1513321 sending unit has 1/2" NPT threads and the ports in some intakes & late 70's cylinder heads are smaller 3/8" NPT. I have seen posts on here where folks have turned the 1/2" sending units down and re-threaded them to 3/8" to get around that issue if necessary.

Finally, this particular sending unit has a "nail head" terminal that works with a Packard/Delphi 56-series terminal and a special slotted plastic connector shell that allows it to slide on sideways.

[broberson]

i have a similar issue. 1970 C10, just put in a 383 stroker, and the temp sender is 3/8 NPT, but now the gauge wont work with the new motor/new sender. with the stock 350 and the 1/2 inch button top sender, it worked fine. Do i need another gauge, or is there another sender I should purchase?
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[jdl71]

The sender is just a variable ground. Turn the key on, ground the sender wire to something and see if the gague moves. This should rule out all except the sender. Then with engine cool check for a short between the contact and body of sender. Also do not use thread tape, the threads provide the ground to the block or whatever it’s screwed in to.

[ray_mcavoy]

Originally Posted by jdl71

The sender is just a variable ground.

True. Although there are many different temperature sending units available and not all of them have the same temperature vs. resistance curve to work correctly with the stock gauge.

It sounds like the sending unit that's in broberson's new engine is not correctly matched to the original gauge in his truck. Or maybe the sending unit in the new engine is the type meant for use with a warning light and not a gauge.

I don't think there are any readily available temp sending units with 3/8" NPT threads that will match the resistance range required for the original gauges in these trucks. However, as I mentioned earlier, some members have taken the original style sending units with 1/2" NPT threads, chucked them into a lathe, turned them down, and re-threaded them to 3/8" NPT. And I believe at least one of those members was offering this as a service for folks without the necessary tooling to do it themselves.

[Captainfab]

You must use the temp sender that is correct for your year truck with a gauge. You will need to either purchase the original style sender with 1/2" NPT and have it machined to 3/8" NPT locally, or contact the member in this thread.

http://www.67-72chevytrucks.com/vboa...d.php?t=726700

Originally Posted by broberson

i have a similar issue. 1970 C10, just put in a 383 stroker, and the temp sender is 3/8 NPT, but now the gauge wont work with the new motor/new sender. with the stock 350 and the 1/2 inch button top sender, it worked fine. Do i need another gauge, or is there another sender I should purchase?
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[A1971Blazer]

I can furnish the correct sender modified to 3/8-NPT...
These are machined on a CNC lathe
This post is not a for sale ad.....

I have sold several of these with 100% positive results
PM for more info

correct part with ½-NPT


re-threaded to 3/8"-NPT


original threads machined off


new thread size machined on

[LostMy65]

Originally Posted by ray_mcavoy

The correct sending unit for use with the original temperature gauge was GM #1513321. Lectric Limited makes an accurate reproduction.

As Captainfab said, the original temperature sending unit wire was dark green. However, instead of being in the loom with the alternator wiring, it was in the engine harness with the starter & coil wiring. That harness has a 6-cavity plug where it goes through the firewall up above the engine over toward the passenger side.

The temp sender wire originally ran along side the coil wiring in that loom and then branched off on it's own near the coil. From there it ran through a section of asphalt coated fabric loom clipped to the side of the valve cover. On inline-6 engines the sending unit was originally located in the lower thermostat housing and on V8 engines it was originally in the intake manifold just off to the driver side of the thermostat housing.

1968 & newer small block Chevys had the temp sender located in the cylinder head between the #1 & #3 spark plugs so you might have to extend / re-route the wire a bit. Although some intake manifolds (especially aftermarket ones) still have a port up near the thermostat. Just be aware that the #1513321 sending unit has 1/2" NPT threads and the ports in some intakes & late 70's cylinder heads are smaller 3/8" NPT. I have seen posts on here where folks have turned the 1/2" sending units down and re-threaded them to 3/8" to get around that issue if necessary.

Finally, this particular sending unit has a "nail head" terminal that works with a Packard/Delphi 56-series terminal and a special slotted plastic connector shell that allows it to slide on sideways.

I have an engine in my 65 that has the sender in the head between 1 & 3. Whatever sender is in there is working for my 65 gauges. So, my heads must be from a 67-72 sbc?

[LostMy65]

Originally Posted by LostMy65

I have an engine in my 65 that has the sender in the head between 1 & 3. Whatever sender is in there is working for my 65 gauges. So, my heads must be from a 67-72 sbc?

So, I have two senders. One in the head and one in the intake manifold. The one in the head reads all the way over to hot, and the one in the manifold reads about 1/4 the way from cool.

[The Rocknrod]

LostMy65 - The correct sending unit GM #1513321 from Lectric Limited? or some other senders?
https://www.lectriclimited.com/elect...ending%20Units

[LostMy65]

Originally Posted by The Rocknrod

LostMy65 - The correct sending unit GM #1513321 from Lectric Limited? or some other senders?
https://www.lectriclimited.com/elect...ending%20Units

Thank you.

[The Rocknrod]

Originally Posted by LostMy65

Thank you.

No I was asking - Do you know if the two you have are the correct senders or not?
So why didnt I just ask?

[LostMy65]

Originally Posted by The Rocknrod

No I was asking - Do you know if the two you have are the correct senders or not?
So why didnt I just ask?

No, I don't know.
They were on my 65 when I found it and bought it back.

[kleeper63]

One of those modified 3/8 NPT senders is exactly what I need. How can I buy two (one for a spare)?

[The Rocknrod]

Originally Posted by kleeper63

One of those modified 3/8 NPT senders is exactly what I need. How can I buy two (one for a spare)?

You contact the member on post #9 above. http://67-72chevytrucks.com/vboard/s...d.php?t=726700