Question about my temp. gauge!!

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My383duster

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Hello Mopar World, I have a 1973 Duster that I have had for 17 year's.I built a 383 &727 and put in it 15 year's agoI drive it on the street and drag race it also.My question is on the factory temperature gauge,I still have all of the original gauges in it.I added a water temp &oil pressure gauge.At what temperature is the coolant when the original gauge in the dash is at the hall way point??. My second temp gauge is just a cheapo p.o.s..and I know it's not correct. I just wanted to know about the original gauge so I can figure out if I am running it to hot, Once I kinda know this,I can go from there.I am thinking it's around 195- 210, Just my guess. Thank you in advance for any information about this.It would help me out. Everyone have a great day.
 
Nobody knows. The factory temp gauge is notoriously slow and not really tied to reality. By the time it tells you the engine is hot, you will know it in other ways, like the steam billowing from under the hood.
Buy an IR gun; it will tell you what you need to know.

BTW;
since we're talking, the thermostat sets the MINIMUM temperature, by CLOSING when the temp is below it's set point. If you have an overheat problem, either the stat is stuck in some position other than open, or you have an efficiency problem.
If it happens at speed, look to a loss of coolant, a lack of circulation, or a plugged up rad.
If it happens while idling in your driveway, look to everything, lol.
Such as;
a missing shroud, a crappy lo-efficiency fan, a slipping belt, a plugged rad, a faulty fan clutch, a really crappy waterpump, or retarded ignition timing. Not to mention a plugged exhaust, but that never happens on our classics..... right?
Your rad when the system is working right , should be able to pull the temp down about 30degrees from inlet to outlet.
 
Last edited:
I did some testing on a temp sender which was supposed to be for a 67 dart 273.


The results were interesting.


Could not screen capture the spread sheet completely

Column A is temperature of a pot of water
Column B is the restance of the sender
Column C is the percentage of gauge movement based on 10, 23 and 72 ohms 10 ohms being full scale (far left)
23 ohms being 1/2 scale (center)
74 ohms being low on scale (far right)

Left and right is based on dodge dart standard cluster.

The 1/4 and 3/4 ohm values are taken from other testing (fuel gauge) that I did with resisters at the sender end.


The 67 dart temp gauge has the "normal" range shifted to the left. It was corrected in 68 or 69.

When my temp guage was functioning correctly it would run just a tad over the left line of "normal" about 1/3 scale when it was cold out. ( That sets it at about 195)

When it is hot out it would run closer to center but enough to the right to put it at about 210.


Hope this info helps.

As AJFormS mentioned if you measure the temp of the thermostat housing or bypass hose or upper rad hose, or all 3 and you look at your temp gauge you can sort of calabrate your OEM gauge.


Screenshot_20220911-210516.png
 
Nobody knows. The factory temp gauge is notoriously slow and not really tied to reality. By the time it tells you the engine is hot, you will know it in other ways, like the steam billowing from under the hood.
Buy an IR gun; it will tell you what you need to know.

BTW;
since we're talking, the thermostat sets the MINIMUM temperature, by CLOSING when the temp is below it's set point. If you have an overheat problem, either the stat is stuck in some position other than open, or you have an efficiency problem.
If it happens at speed, look to a loss of coolant, a lack of circulation, or a plugged up rad.
If it happens while idling in your driveway, look to everything, lol.
Such as;
a missing shroud, a crappy lo-efficiency fan, a slipping belt, a plugged rad, a faulty fan clutch, a really crappy waterpump, or retarded ignition timing. Not to mention a plugged exhaust, but that never happens on our classics..... right?
Your rad when the system is working right , should be able to pull the temp down about 30degrees from inlet to outlet.
Nobody knows. The factory temp gauge is notoriously slow and not really tied to reality. By the time it tells you the engine is hot, you will know it in other ways, like the steam billowing from under the hood.
Buy an IR gun; it will tell you what you need to know.

BTW;
since we're talking, the thermostat sets the MINIMUM temperature, by CLOSING when the temp is below it's set point. If you have an overheat problem, either the stat is stuck in some position other than open, or you have an efficiency problem.
If it happens at speed, look to a loss of coolant, a lack of circulation, or a plugged up rad.
If it happens while idling in your driveway, look to everything, lol.
Such as;
a missing shroud, a crappy lo-efficiency fan, a slipping belt, a plugged rad, a faulty fan clutch, a really crappy waterpump, or retarded ignition timing. Not to mention a plugged exhaust, but that never happens on our classics..... right?
Your rad when the system is working right , should be able to pull the temp down about 30degrees from inlet to outlet.
Nobody knows. The factory temp gauge is notoriously slow and not really tied to reality. By the time it tells you the engine is hot, you will know it in other ways, like the steam billowing from under the hood.
Buy an IR gun; it will tell you what you need to know.

BTW;
since we're talking, the thermostat sets the MINIMUM temperature, by CLOSING when the temp is below it's set point. If you have an overheat problem, either the stat is stuck in some position other than open, or you have an efficiency problem.
If it happens at speed, look to a loss of coolant, a lack of circulation, or a plugged up rad.
If it happens while idling in your driveway, look to everything, lol.
Such as;
a missing shroud, a crappy lo-efficiency fan, a slipping belt, a plugged rad, a faulty fan clutch, a really crappy waterpump, or retarded ignition timing. Not to mention a plugged exhaust, but that never happens on our classics..... right?
Your rad when the system is working righat , should be able to pull the temp down about 30degrees from inlet to outlet.
Thank you for the info, I have a IF gun,A radiator thermometer and have checked the coolant temp with both at the same time to see which one of my gauges are close to being correct.The radiator is a 3 core fairly new and coolant is moving through it good. I only use distilled water with just enough antifreeze to protect at 20 degrees.I have a aluminum mopar performance Water Pump,A Stant 185 degree thermostat that I checked with a pan of water on the stove and it's good according to my rad thermometer and i f gun.I have 2 14" 2200 rpm electric fans with a flat shroud that is sealed around the rad core, It's pulling a lot of air through the rad.The belt running the water pump is running directly from the crank pulley with a adjustable idler pulley and is not slipping.I have the timing set at 18 degrees BTC, This is where it runs the best and no clattering.I have to run premium or 100 octane AV fuel in it do to the 11>1 dome pistons, Running ND Accel colder plugs in it also.. It has Hooker Comp.fenderwell headers with 3" exhaust with 12" long Magnaflow mufflers and turn out in front of the rear MT et streets.With all of this being said I build race engine's and Tranny's and rear end's when I am not at work.I work for John Deere as a Tractor and small engine tech.I have built for myself over the years a 71 Plymouth Satellite,A 69 GTX,A 70 Roadrunner,A Plymouth Arrow truck that I gutted and put a 440 in it.( That one was a crazy one). And this Duster.. Now back to the original question ,It has only puked out coolant a couple of times if I was running back to back passes at the track, It's never done it on the street.But,In traffic the original temp gauge will creep up to almost center position,And my cheapo secondary temp gauge is reading 220 but I know it's 12 degrees fast.. This is where it's kinda confusing:: When I was checking the coolant temp with my rad thermometer and I f gun they are reading 2 different temps.. When the original gauge is in between the normal and middle position my rad thermometer is reading 186 and my I f gun is reading 174 at the radiator cap opening.My crappy second gauge will be reading 210-220 But like I said, I Know it's not correct.I am reading 176 at the top of the rad and 134 at the bottom of the rad.The rad intake hose will be reading 174 while the upper return hose will be reading 181 just above the thermostat housing and reading 189 at the top of the return hose at the radiator.I just kinda wanted to know if the original gauge is somewhat close to the coolant temperature. I think I am gonna go between my two gauges and call it at that for now.I am gonna order a good secondary gauge so I can figure out if it's really getting to warm or if it's not.You did answer my question about the original gauge and I really appreciate it.That's why I am on your Forum.I can always get a correct answer when I need it!!. Thank you very much for your help and have a good night. I will tune back in once I get the new secondary gauge put in the old girl.
 
Thank you for the info, I have a IF gun,A radiator thermometer and have checked the coolant temp with both at the same time to see which one of my gauges are close to being correct.The radiator is a 3 core fairly new and coolant is moving through it good. I only use distilled water with just enough antifreeze to protect at 20 degrees.I have a aluminum mopar performance Water Pump,A Stant 185 degree thermostat that I checked with a pan of water on the stove and it's good according to my rad thermometer and i f gun.I have 2 14" 2200 rpm electric fans with a flat shroud that is sealed around the rad core, It's pulling a lot of air through the rad.The belt running the water pump is running directly from the crank pulley with a adjustable idler pulley and is not slipping.I have the timing set at 18 degrees BTC, This is where it runs the best and no clattering.I have to run premium or 100 octane AV fuel in it do to the 11>1 dome pistons, Running ND Accel colder plugs in it also.. It has Hooker Comp.fenderwell headers with 3" exhaust with 12" long Magnaflow mufflers and turn out in front of the rear MT et streets.With all of this being said I build race engine's and Tranny's and rear end's when I am not at work.I work for John Deere as a Tractor and small engine tech.I have built for myself over the years a 71 Plymouth Satellite,A 69 GTX,A 70 Roadrunner,A Plymouth Arrow truck that I gutted and put a 440 in it.( That one was a crazy one). And this Duster.. Now back to the original question ,It has only puked out coolant a couple of times if I was running back to back passes at the track, It's never done it on the street.But,In traffic the original temp gauge will creep up to almost center position,And my cheapo secondary temp gauge is reading 220 but I know it's 12 degrees fast.. This is where it's kinda confusing:: When I was checking the coolant temp with my rad thermometer and I f gun they are reading 2 different temps.. When the original gauge is in between the normal and middle position my rad thermometer is reading 186 and my I f gun is reading 174 at the radiator cap opening.My crappy second gauge will be reading 210-220 But like I said, I Know it's not correct.I am reading 176 at the top of the rad and 134 at the bottom of the rad.The rad intake hose will be reading 174 while the upper return hose will be reading 181 just above the thermostat housing and reading 189 at the top of the return hose at the radiator.I just kinda wanted to know if the original gauge is somewhat close to the coolant temperature. I think I am gonna go between my two gauges and call it at that for now.I am gonna order a good secondary gauge so I can figure out if it's really getting to warm or if it's not.You did answer my question about the original gauge and I really appreciate it.That's why I am on your Forum.I can always get a correct answer when I need it!!. Thank you very much for your help and have a good night. I will tune back in once I get the new secondary gauge put in the old girl.
Man, I don't know what I did to your response.It's showing it 3 times now, Sorry bout that.One thing I do know is this phone is definitely a lot smarter than myself.
 
I did some testing on a temp sender which was supposed to be for a 67 dart 273.


The results were interesting.


Could not screen capture the spread sheet completely

Column A is temperature of a pot of water
Column B is the restance of the sender
Column C is the percentage of gauge movement based on 10, 23 and 72 ohms 10 ohms being full scale (far left)
23 ohms being 1/2 scale (center)
74 ohms being low on scale (far right)

Left and right is based on dodge dart standard cluster.

The 1/4 and 3/4 ohm values are taken from other testing (fuel gauge) that I did with resisters at the sender end.


The 67 dart temp gauge has the "normal" range shifted to the left. It was corrected in 68 or 69.

When my temp guage was functioning correctly it would run just a tad over the left line of "normal" about 1/3 scale when it was cold out. ( That sets it at about 195)

When it is hot out it would run closer to center but enough to the right to put it at about 210.


Hope this info helps.

As AJFormS mentioned if you measure the temp of the thermostat housing or bypass hose or upper rad hose, or all 3 and you look at your temp gauge you can sort of calabrate your OEM gauge.


View attachment 1715984399
Thank you very much for this information!!. The results are very interesting,but Very good information to know.I really appreciate your help and time on this. I'm gonna print this out so I can try it.Hope you have a great day Dana67Dart.
 
Probably the best way to "calibrate" your dash temperature gage is to note where the needle likes to stay once the engine is warm. If the T-stat is controlling and not pegged open (overheating), then the stamp on the T-stat (180 or 190 F) is likely where the needle is. That said, there is variation between T-stats and no T-stat controls an exact temperature. Under higher thermal loads, the T-stat must open more, and that only happens if the coolant temperature is higher. Thus, it will control a little hotter under load (racing up a mountain road on a hot summer day). If you have a T-stat out, test it in a pot of hot water. I got amazingly consistent readings shooting at in underwater w/ an IR gun against a thermometer in the water. Note that an IR gun views a larger area than just where the red laser dot hits, so get it close enough to fill the view circle with the hot surface. Harder to get consistent readings shooting at the engine's head or T-stat housing.
 
Probably the best way to "calibrate" your dash temperature gage is to note where the needle likes to stay once the engine is warm. If the T-stat is controlling and not pegged open (overheating), then the stamp on the T-stat (180 or 190 F) is likely where the needle is. That said, there is variation between T-stats and no T-stat controls an exact temperature. Under higher thermal loads, the T-stat must open more, and that only happens if the coolant temperature is higher. Thus, it will control a little hotter under load (racing up a mountain road on a hot summer day). If you have a T-stat out, test it in a pot of hot water. I got amazingly consistent readings shooting at in underwater w/ an IR gun against a thermometer in the water. Note that an IR gun views a larger area than just where the red laser dot hits, so get it close enough to fill the view circle with the hot surface. Harder to get consistent readings shooting at the engine's head or T-stat housing.

Thank you for the information, I did some more testing on the thermostat, Coolant Flow, Radiator and Wiring.. I removed the T-Stat and checked it again in a pan of water on the stove.I have a KD Tools rad thermometer and the i f gun,Had the rad thermometer against the T-Stat and the I f gun just above the water The T-stat is a Stant Super Stat 180° and it started opening at 178° , Fully open at 181° according to my rad thermometer.My i f gun is reading exactly 11° cooler.I checked my Rad thermometer with another one I have and it is reading the same,So now I know for sure my rad thermometer is correct and my i f gun is not.I put the T-Stat back in filled with coolant, Started checking the wiring to the factory gauge and didn't find any problems with this.I put a new gauge sensor in the water pump housing for the original gauge.Started it up and let it idle with my rad thermometer in the radiator and waited for it to get around 175° .The coolant just started flowing at 178° ,So I ran around to look at the factory gauge and it was sitting right on the normal line ( The first line after the gap in the gauge). So what this showed me is my factory gauge is really close to T-stat opening up.I took it out for a drive and hammered on it pretty hard off & on for 6 miles and took her back home.The factory gauge rose up about a 1/16 of an inch above normal the entire time.When I was going back home the gauge ran in the normal range and done great.. I was happy after this,So the only thing I replaced was the old gauge sensor, Everything else was reading good. I think I am good to go now with your help on this.A lot of checking and didn't think about the gauge sensor.Man,I usually catch things like this before hand, Especially since the sensor is the original one...I want to thank you for the help and diagram that you sent me.I think my memory is catching up with my age . My dad always told me,Start from the beginning of the problem and go forward from there!!. He was a Diesel & Gasoline engine mechanic, for a big construction company with heavy equipment.I started following him around at 9 yrs.old and he thought me sooo much stuff.Thank you again for all of your help.I am gonna try to close this thread now that y'all helped me figure it out.Many blessings for the help..IF IT AIN'T A MOPAR IT AIN'T WORTH FIXEN!!.
 
BTW

Coolant temp and radiator temp might not read the same, manifold and head and block temps also.

Air moving over the metal of the rad might make the outside of the rad cooler.

Same for versions parts of the engine.


ALSO...

IR temp reading devices are sensitive to metal reflectiveness.

They are not so accurite on shinny objects.

Your temp pickups are located in the coolant flow, the coolant in the rad is only a percentage of the coolant flowing through the system unless the thermostat is fully open so the temp readings there might not be accurite either.

I would say that the closest you are going to get is the rad thermostat in the top of the tank in the coolant.

You don't need to accurite to withing 1/2 a degree of you are within +/- 5 deg your good.
 
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