[johnonetrillion]

I’ll get my auto elec to solder a short patch wire with a 22 ohm resistor in place and will test before changing out.

Interested to learn if that scale is flat or curved. Thinking ... when a car starts to overheat the dial moves quickly at the end. Is that a function of the gauge or the sender? (As I write this, I suspect it is more likely the former.)

 

[Roscoe7]

I’ll get my auto elec to solder a short patch wire with a 22 ohm resistor in place and will test before changing out.

Interested to learn if that scale is flat or curved. Thinking ... when a car starts to overheat the dial moves quickly at the end. Is that a function of the gauge or the sender? (As I write this, I suspect it is more likely the former.)

I went through the same exercise 'centering' my temp gauge after the LS swap.

I went down to JCAR, picked up various resistance resistors, a packet of male, and a packet of female insulated crimp terminals (red = 1.5mm) and produced a few of these.



I plugged them in, in series between the factory wire and temperature gauge.

Admittedly on a 57, but you can get your arm up the rear of the cluster ok, so I tried each one until I was happy with where the gauge was reading (centre).

The final one, I removed, added a short piece of heat shrink (from lug to lug to add some strength), and reinstalled. The one in the photo above was one of the 'test' ones.

Cheap, easy, DIY, and can be removed easily if required.

Hope this helps. Cheers.

 

[stoveboltgeek]

I’ll get my auto elec to solder a short patch wire with a 22 ohm resistor in place and will test before changing out.

Interested to learn if that scale is flat or curved. Thinking ... when a car starts to overheat the dial moves quickly at the end. Is that a function of the gauge or the sender? (As I write this, I suspect it is more likely the former.)

Good question. My rough guess - making several assumptions, including that the sending unit's response is linear - is a '56 gauge would measure 180 degrees as about 190 with a '57 sending unit. Of course, if your particular sending unit is on the low side of the spec, it would read even higher.

If I recall correctly, when testing the sending unit I put in my '57, the gauge was at the "hot" line at about 195 or 200. So, if you're at 185 at the sending unit....

 

[nad427]

On top of all the great technical advice here, it would still be nice to know at what temp the thermostat starts to open, and if it's opening up all the way when it's supposed to.

By checking it, it would at least give you some peace of mind by knowing that it's doing what it should, and when it should. After that match the gauge reading to the thermo's actions and you've got that part of it licked.

If the motor still shows signs of overheating after the gauge readings are right, then would be the time to look deeper into the cooling system parts.

 

[stoveboltgeek]

On top of all the great technical advice here, it would still be nice to know at what temp the thermostat starts to open, and if it's opening up all the way when it's supposed to.

By checking it, it would at least give you some peace of mind by knowing that it's doing what it should, and when it should. After that match the gauge reading to the thermo's actions and you've got that part of it licked.

If the motor still shows signs of overheating after the gauge readings are right, then would be the time to look deeper into the cooling system parts.

Am I understanding you correctly - that you're suggesting we check the obvious first??? :sign0020:

 

[pauldian]

Sounds logical to me ! :flag6:

 

[johnonetrillion]

Sounds logical to me !

Ja I got a new thermostat last week and tested it last night. It opened at 160 and then reached maximum (shown) at about 185. I would have thought it would open further?

Will get the other one out and test similarly.

And ... I know for the sake of process it is wise to change only one thing at a time.

 

[nad427]

Am I understanding you correctly - that you're suggesting we check the obvious first??? :sign0020:

I have to admit that, that common sense statement is a novel idea to me. I'm more guilty than most of over-teching myself when problem solving most times.

 

[stoveboltgeek]

I have to admit that, that common sense statement is a novel idea to me. I'm more guilty than most of over-teching myself when problem solving most times.

Just so everyone knows - I'm coming at the problem from a little bit different perspective.

I'd noticed this thread, but it looked like things were progressing well, so I didn't jump in.

A couple of days ago, John PM'd me, asking if I knew the specification for the resistance of a '56 sending unit at 180 degrees. I guess I'm geeky enough, that if anybody would have that spec sitting around, it would be me.

Well, I didn't have any idea what that would be. But, I knew how to solve that problem. Soooo.....

 

[stoveboltgeek]

So, the story gets a little more interesting.

I talked to my buddy who I thought might have a NOS '57 sending unit. He didn't, but he did have an original used one.

In addition to that, he's partially built a test circuit where he can wire up temperature and gas gauges, and test them out. He offered to loan that to me.

In the meantime, I made an interesting discovery. It turns out the '57 temperature sending units are still available from GM, but the part number has changed.

As you know, AC-Delco often has their own part numbering system that's independent of the GM part number used at the parts counter. This is a case in point.

In the pictures below (from an old eBay listing), you see that the '57 sending unit 1513321 is also known by the Delco part G1852. Rockauto has it available - here's the G1852 description: https://www.rockauto.com/en/moreinfo.php?pk=98816&jsn=260 .

You'll note there's a cosmetic difference between the two - the black insulator is smaller in the new version. But, it's the electrical characteristics I care about.

It's going to be a week or two before I can pull everything together. But, it looks like I'll be able to measure resistance vs. temperature on a NOS '56, a current-production '57, and aused '57 sending unit. Given those measurements, I can then dial in the resistance values measured and show what that should look like on original temperature gauges.

I'll probably start that as a new thread, in case it ends up as a sticky thread.

 

[johnonetrillion]

So here’s what I have to test the current sender.

Will do that at the time I swap out for the NOS one that’s on the way.

 

[stoveboltgeek]

So here’s what I have to test the current sender.

Will do that at the time I swap out for the NOS one that’s on the way.

Yep - that's what you need. (red, red, black, gold = 22 ohm, 5%)

Why don't you try putting it in now, and see what happens? (wrap the exposed part in electrical tape after installing)

 

[hotrodg726]

So here’s what I have to test the current sender.

Will do that at the time I swap out for the NOS one that’s on the way.

if your current sender unit uses a flat spade connector then I can guarantee it is the wrong sender. the resistor may work.

 

[johnonetrillion]

if your current sender unit uses a flat spade connector then I can guarantee it is the wrong sender. the resistor may work.

Ja. I have a correct replacement for ‘56 on the way.

 

[johnonetrillion]

Here’s what 22 ohms does

With and without ...

 

[angs1957]

With is where they normally sit, you`ll find it will rise as it gets hotter

 

[stoveboltgeek]

As Angelo said - that's exactly how it should read.

So, the spec we found the other day appears to be correct. And, the various sending units I mentioned will be in my hands in a few days, so I'll be able to take some measurements.

 

[Carmine]

With and without ...

Sorry, I can't help you with your temp. issue, but if you don't mind me asking, I have another question for you. I see in your shifting bezel, you have an overdrive transmission. What is the shifting like going from L-1 to OD, manually?? Is it sloppy?? Do you have the tendency of going past the gear you want, to the next highest gear?? Thanks, Carmine.

 

[johnonetrillion]

Sorry, I can't help you with your temp. issue, but if you don't mind me asking, I have another question for you. I see in your shifting bezel, you have an overdrive transmission. What is the shifting like going from L-1 to OD, manually?? Is it sloppy?? Do you have the tendency of going past the gear you want, to the next highest gear?? Thanks, Carmine.

It's perfect. The whole rig was installed by a trans shop.

 

[johnonetrillion]

Pics of temp gauge and readings from just after a hot morning driving.

Edit: This is freeway driving followed by some slow driving. From this point if I get back up to speed again it cools to normal.