What does the temp gauge represent?

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Serj22

Serj22

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I have ordered a new temperature gauge that shows actual numbers on it, but I have not gotten it yet. I am curious what the gauge that's stock in my 1968 Dodge Dart is supposed to represent (like where is 100* or 200* for example?)

Basically, I am trying to figure out my heating/cooling situation.

I made this really cute diagram to help explain.

[ame="http://s43.photobucket.com/user/serj22/media/tempgauge_zpsc10abf84.png.html"]tempgauge_zpsc10abf84.png Photo by serj22 | Photobucket@@AMEPARAM@@http://i43.photobucket.com/albums/e356/serj22/tempgauge_zpsc10abf84.p@@AMEPARAM@@43.photobucket.com/albums/e356/serj22/tempgauge_zpsc10abf84.p[/ame]

When I bought the car, it consistantly ran at #1 and stayed there during 65mph operation and even in town. It never went up, and if it did, it didn't ever go as high as #2.

I noticed the radiator was low as some of the coolant had recently been puked (on accident by my own doing seeing what the vent did). I added about 1 quart of fluid to it, and then it ran in the "C" range a lot longer than it used to, but at 65mph, the gauge is almost consistantly at #2. When I push the car, like to pass someone, or if I'm running it for extended periods (more than 20 minutes) it gets to #3, and if I idle for a bit, it quickly drops to somewhere between 1 and 2.

I need to know what this gauge was supposed to represent? I'm thinking maybe the thermostat was stuck open somehow and now is malfunctioning? I know it's easy to replace them, but I'd like to know what temps it is hitting before cooling, etc. And I'm still a week away from receiving my new gauge and still drive the car everyday. Hopefully someone has some insight.
 
It's probably just fine, even though it's not actually telling you that in degrees.

On the other hand it might not have a thermostat in it.

1 = borderline cold (160 or less)
2 = about normal but a little cool (170-175)
3 = pretty normal (maybe 190)

Just a guess from experience.
 
TrailBeast said:
It's probably just fine, even though it's not actually telling you that in degrees.

On the other hand it might not have a thermostat in it.

1 = borderline cold (160 or less)
2 = about normal but a little cool (170-175)
3 = pretty normal (maybe 190)

Just a guess from experience.
Click to expand...

So 190 is about 1/2 way inbettween the second arch? I assumed the needle vertical was the normal optimum temp. I always thought based on its representation 3 was close to overheating, but I guess not. So far this is good info. Thank you.
 
These instruments are range indicators. There are no numerical values for hash marks on the screens. If you removed the gauge you would see target dots ( 1 or 3 depending on what gauge it is ) on its perimiter that do have Ohms values.
 
I have a 190 thermostat in my car and my gauge reads here where the exclamation point is located:

C|-|-!-----|-|H

Not here like a previous member stated:

C|-|---!---|-|H

Now, not saying he's wrong and I'm right. The whole point of me saying this is, wiring makes a big difference.

I don't know if temp gauges work the same fashion as fuel gauges (ground out the wire at the sending unit and the gauge reads full VS. ground out and the gauge reads "H") or if it's backwords. But if it works like a fuel gauge, old broken down wires and bad connections can make my 190 degrees appear closer to "C" than the '70 /6 Dart sitting beside me in a parking lot. And the one on the other side of that car can be lower than mine while the next identical car could read the highest. And to make it a little more crazy, if there is a bad connection and ambient temperature changes, so will the gauge reading (bad connection will pass more voltage when hot VS. cold cause of thermal expansion of the copper connectors making a tighter fit and better connection, BOOM gauge reading changes).

Further more, as other members are hinting, these gauges are not calibrated meaning the markings don't correlate with any given temperature. That's the thing I hate about these types of guages, they don't give numbers and they're just there for normality. In other words, the factory says its YOUR responsibility as the driver to pay attention to where it normally is and if one day it varies too much YOU have to make a judgement call as far whether you're ok or if you need to get off on the side of the road. Normality works, but it sucks like in your case where you just bought it (I think) and you don't know "the norm".

That said, I think by what you have told us, you do not have a thermostat in you're car or it's failed and stuck open. If you are truly paranoid and want to know the answer now instead of waiting for the new gauge (I would be paranoid), get an infared thermometer and point it at the thermostat housing after you have ran the car for awhile to get up to temperature. If you can't obtain one of those, take you're radiator cap of and stick the thermometer in the opening, start the car and wait till the thermostat opens and see what the temp is (if water flows into the radiator as soon as you start it and the motor is cold, your thermostat either does not exist or it is stuck open, either one prompts replacement).

If any information I laid out here is wrong, please somebody correct me. I'm just a 19 year old behind a computer so I haven't been around the block like some of you seasoned mopar vets.
 
You could easily "calibrate" your factory gauge in a way that would be fairly meaningful. HOWEVER this "calibration" would depend on a few things:

1--That the wiring harness, connections, etc, in the SYSTEM that is the temp gauge is in good condition

2--That the voltage limiter is stable, IE not a 40 year old mechanical one.

3--That even though the gauge itself is "elderly," that it too is in a condition that can give repeatable readings.

4--Likewise that the sender is in good condition.

All you really need to do is 1 of 2 things.

A---Just use a second gauge or thermometer to "track" readings on the gauge as the engine warms up

B--Remove the sender and using a heater and water, measure ohmic values of the sender at different temperatures. Then you can substitute those readings for the sender into the gauge circuit and notate where the gauge reads at what resistance.

(Somewhere buried in the wonderland of engineering specs is a chart of the thermister temp/ resistance curve of these senders. I don't have it.)

These are the approximate factory values for empty, 1/2, and full readings on the gauge units. Temp, fuel, and oil (if equipped) gauge units are the same electrically

L = 73.7 Ohms (empty)
M = 23.0 Ohms (1/2)
H = 10.2 Ohms (full)
 
/6 Matt said:
I have a 190 thermostat in my car and my gauge reads here where the exclamation point is located:

C|-|-!-----|-|H

Not here like a previous member stated:

C|-|---!---|-|H

Now, not saying he's wrong and I'm right. The whole point of me saying this is, wiring makes a big difference.

I don't know if temp gauges work the same fashion as fuel gauges (ground out the wire at the sending unit and the gauge reads full VS. ground out and the gauge reads "H") or if it's backwords. But if it works like a fuel gauge, old broken down wires and bad connections can make my 190 degrees appear closer to "C" than the '70 /6 Dart sitting beside me in a parking lot. And the one on the other side of that car can be lower than mine while the next identical car could read the highest. And to make it a little more crazy, if there is a bad connection and ambient temperature changes, so will the gauge reading (bad connection will pass more voltage when hot VS. cold cause of thermal expansion of the copper connectors making a tighter fit and better connection, BOOM gauge reading changes).

Further more, as other members are hinting, these gauges are not calibrated meaning the markings don't correlate with any given temperature. That's the thing I hate about these types of guages, they don't give numbers and they're just there for normality. In other words, the factory says its YOUR responsibility as the driver to pay attention to where it normally is and if one day it varies too much YOU have to make a judgement call as far whether you're ok or if you need to get off on the side of the road. Normality works, but it sucks like in your case where you just bought it (I think) and you don't know "the norm".

That said, I think by what you have told us, you do not have a thermostat in you're car or it's failed and stuck open. If you are truly paranoid and want to know the answer now instead of waiting for the new gauge (I would be paranoid), get an infared thermometer and point it at the thermostat housing after you have ran the car for awhile to get up to temperature. If you can't obtain one of those, take you're radiator cap of and stick the thermometer in the opening, start the car and wait till the thermostat opens and see what the temp is (if water flows into the radiator as soon as you start it and the motor is cold, your thermostat either does not exist or it is stuck open, either one prompts replacement).

If any information I laid out here is wrong, please somebody correct me. I'm just a 19 year old behind a computer so I haven't been around the block like some of you seasoned mopar vets.
Click to expand...

I wasn't trying to tell him that everything was fine, but about the temp his guage is showing.
Do note that the 3rd diagram is only about half way up the guage range, not showing hot just because the needle is leaning that way from straight up and down.
And of course he'll have to figure out what it is actually doing, but if I lived in Cal at this time of year and my guage went up to where the third diagram showed, I wouldn't be too worried if thats all it did.
That was my point.

And No you are not wrong. :)
 
TrailBeast said:
I wasn't trying to tell him that everything was fine, but about the temp his guage is showing.
Do note that the 3rd diagram is only about half way up the guage range, not showing hot just because the needle is leaning that way from straight up and down.
And of course he'll have to figure out what it is actually doing, but if I lived in Cal at this time of year and my guage went up to where the third diagram showed, I wouldn't be too worried if thats all it did.
That was my point.

And No you are not wrong. :)
Click to expand...
I know you wasn't trying to tell him that everything was but I was merely using you as a "case in point" example. I agree as far as everything else you say, a California car will definitely run warmer than mine lol!

BTW, thanks for confirming my information to be correct. I always worry when I give advice like that because of my age and experience. I haven't been around the block for 50+ years like some of the old salts on here and I trust anybody who's knows correct will set me straight regardless of age. Gotta love this site!:glasses7:
 
It's true I have only owned the car for about 2 months, so the only way I know it to run is how I described. It ran at #1 till I added more coolant about a week ago. I like the info here. It's all been very enlightening. I was slightly worried that the meter line down toward the "C" was below operating temp and straight vertical was somehow optimum.
 
Better off with a manual type guage.
Not electric, the kind that shows the temp if the car is running or not.

To keep it factory and know for sure what is going on would require putting a thermometer on it and find out.

Also could'nt hurt to give it a good reverse flush (It's free and can solve these kinds of problems)
 
TrailBeast said:
Better off with a manual type guage.
Not electric, the kind that shows the temp if the car is running or not.

To keep it factory and know for sure what is going on would require putting a thermometer on it and find out.

Also could'nt hurt to give it a good reverse flush (It's free and can solve these kinds of problems)
Click to expand...

Reverse flush?
 
Check your cap, it may not be holding the pressure you think it should. 2 out of 3 of mine were bad recently (I have 3 Barracudas in various state of disrepair).
 
Borrow your wife's meat thermometer and open cap (when cold) and stick it in and start car. As temp on gauge rises compare to thermometer and you'll know what your gauge reads on your car. Did this with mine and found that your #3 pic was 185 on my car. No more worries.
 
64conv65hard said:
Borrow your wife's meat thermometer and open cap (when cold) and stick it in and start car. As temp on gauge rises compare to thermometer and you'll know what your gauge reads on your car. Did this with mine and found that your #3 pic was 185 on my car. No more worries.
Click to expand...

I'm going to try this. So far I have been trying ot find where she keeps it. I do not want to ask her for it, because she'll ask what I am going to do with it, and I don't want to answer that question.
 
Better to ask her and explain first instead of her catching you, too late for explanations then. Hot soapy water will clean it and tell her you get the first piece of meat when she reuses it.
 
95teetee said:
haven't you heard the saying "it's easier to ask for forgiveness than for permission"?

:D
Click to expand...

Not with my wife..... She always hits me with the line: "You knew I would say no, but you did it anyway."

At that point, I'm basically screwed.

Followed by her going out and buying a pair of $200 shoes that will never be taken out of the box, except to show me that she went out and bought a pair of $200 shoes that will never be taken out of the box........
 
I would get an infrared gun so you can shoot it at different points and see what the real numbers are. You can even shoot it right next to the temperature sending unit. They are cheap at Harbor Freight.
 
1968FormulaS340 said:
Not with my wife..... She always hits me with the line: "You knew I would say no, but you did it anyway."

At that point, I'm basically screwed.

Followed by her going out and buying a pair of $200 shoes that will never be taken out of the box, except to show me that she went out and bought a pair of $200 shoes that will never be taken out of the box........
Click to expand...
That's amusing....... I forsee my future with my lady to be of a similar likeness.
 
I would use the infrared gauge on the Mrs., but I don't think they read in the negative temp range....do they???
 
They could read in the negative range for that... in theory.

I bought a new venting cap. The old one was much larger than the "correct" one and was much easier to tighten down and take off. I also picked up a recirculating kit and mounted it near the horns and ran the hose to the bottom of it, rather than to the ground. Still running about the same, and my new gauge was apparently on backorder, so never showed. Now I'm off to find a cheapie and find out what's what.
 
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