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Coolant temp sender ohm range

dan juhasz

dan juhasz

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As far as I know the range for the coolant temp sender for a 69 Charger is 10 to 73. 73 being cold and 10 bring 250 degrees. I’ve bought numerous ones and none fall into those specs and of course the gauge either never comes off cold or hovers at 250 on the gauge. Does anyone sell a proper sender?
 
Sender at 68f room temp should read in the ball park of 360 ohms. 73 would be bottom of the actual gauge scale and 10 at full gauge.
 
dadsbee said:
Sender at 68f room temp should read in the ball park of 360 ohms. 73 would be bottom of the actual gauge scale and 10 at full gauge.
Click to expand...
isn’t 73 and 10 the range in ohms of the sender itself ? Where does 360 ohms fit in, I’m not following?
 
NO, that is the ohm range to make the gauge read... from what 160f to 260? On a bench at room temp, somewhere around 360.
 
Here is some notes I have from when I calibrated my 1969 Rally dash:
At 120 degrees water temp (first mark on gauge), the sending unit (unloaded, connected to DMM) read 84.3 Ohms.
To get the same first mark position on the gauge with a 5-volt power supply took 62 Ohms of resistance and drew 62.1 mA of current.
At 150 degrees water temp (about 1/2 way between first mark and second mark) the sender showed 49.5 Ohms unloaded.
To get same position with 5v took 33 Ohms and current was 98.8 mA.
At 170 (second mark on gauge) sender unloaded was 37.5 Ohms
Loaded @ 5 volts took 22 Ohms and 119.7 mA
At 180 (needle straight up) 30.4 Ohms unloaded sender reading.
Loaded @ 5 volts 20 Ohms and 130.0 mA
I could not check sender resistance above boiling point (not pressurized when testing)
The next high temp mark, I think might be about 225-230? loaded @ 5 volts took 13 Ohms and 160 mA
Full scale (I think 240?) took 12 Ohms and 163 mA

Note that 5 volts was used for the Instrument Voltage Regulator (IVR) because I converted the factory one to solid state.
 
I bought the gauge style but I cannot remember the part number from Year One.
Works correctly.
Use sealer not thread tape.
 
The values in Red diamonds on the graph are extrapolated based on the curve I don't have a way to get the water above 210 deg

The Red Squares are the gauge readings 0 = cold, 25 = 1/4 scale, 50= 1/2 scale etc

My thermostat is 180 deg and my gauge sits at between 1/4 and 1/2, so in the 190 to 215 deg range

1755370844792.png
 
451Mopar said:
Here is some notes I have from when I calibrated my 1969 Rally dash:
At 120 degrees water temp (first mark on gauge), the sending unit (unloaded, connected to DMM) read 84.3 Ohms.
To get the same first mark position on the gauge with a 5-volt power supply took 62 Ohms of resistance and drew 62.1 mA of current.
At 150 degrees water temp (about 1/2 way between first mark and second mark) the sender showed 49.5 Ohms unloaded.
To get same position with 5v took 33 Ohms and current was 98.8 mA.
At 170 (second mark on gauge) sender unloaded was 37.5 Ohms
Loaded @ 5 volts took 22 Ohms and 119.7 mA
At 180 (needle straight up) 30.4 Ohms unloaded sender reading.
Loaded @ 5 volts 20 Ohms and 130.0 mA
I could not check sender resistance above boiling point (not pressurized when testing)
The next high temp mark, I think might be about 225-230? loaded @ 5 volts took 13 Ohms and 160 mA
Full scale (I think 240?) took 12 Ohms and 163 mA

Note that 5 volts was used for the Instrument Voltage Regulator (IVR) because I converted the factory one to solid state.
Click to expand...
When I was checking the sending unit unloaded, I just had it in a Pyrex container on the stove with a digital thermometer. Because I didn't have a way to stabilize the temp the thermometer likely responded quicker than the bulkier factory sending unit, so the factory sending unit seems to respond slower to the actual temp resulting in higher readings the way I tested it. Testing oil pressure was easier, just used compressed air and a regulator to set different pressures.
Fuel gauge measured 73 Ohms Empty (lower stop), 9.6 Ohms Full (upper stop), and about 31 Ohms 1/2 way between the stops.
For the calibration @ 5 Volts, 51 Ohms seemed to move the needle to the Empty mark, 33 Ohms to 1/4 mark, 20 Ohms to 1/2 mark, 15 Ohms to 3/4 mark, and 10 Ohms to the full mark.
Oil pressure was like 51 to 43 Ohms just to read about 0 PSI, 15 PSI = 30 Ohms, 20 PSI = 28 ohms (two 56 Ohm resistors in parallel), 40 PSI = 20 Ohm, 60 PSI = 16 Ohm, 80 PSI = 9.79 Ohm (10-ohm in parallel with 470-ohm).
 
451Mopar said:
Fuel gauge measured 73 Ohms Empty (lower stop), 9.6 Ohms Full (upper stop), and about 31 Ohms 1/2 way between the stops.
Click to expand...
fuel gauge does not sit 1/2 way between the stops at 1/2 a tank due to the shape of the tank. If the tank was a perfect rectangle then it would be more likely to be that way depending on where the sender was mounted on the tank.

If you really want to know put the sender in the tank and have the car on flat ground. empty the tank completely then add 1 gallon of fuel and jostle the car. measure the resistance rinse and repeat till the tank is full. Assuming an 18 gallon tank at 9 gallons you should read about 23 ohms


451Mopar said:
For the calibration @ 5 Volts, 51 Ohms seemed to move the needle to the Empty mark, 33 Ohms to 1/4 mark, 20 Ohms to 1/2 mark, 15 Ohms to 3/4 mark, and 10 Ohms to the full mark.
Oil pressure was like 51 to 43 Ohms just to read about 0 PSI, 15 PSI = 30 Ohms, 20 PSI = 28 ohms (two 56 Ohm resistors in parallel), 40 PSI = 20 Ohm, 60 PSI = 16 Ohm, 80 PSI = 9.79 Ohm (10-ohm in parallel with 470-ohm).
Click to expand...
Unless you have a 5V solid-state IVR the voltage to the gauge will make a difference on the gauge readings, as will the wire and resistance (mounted in the car) bulkhead connector terminals etc.

20psi at 28 ohms should have the gauge at about 1/2 scale

This is what I got with various A Body senders and for the gauge reading (Red Triangles) I used several 100W 10 ohm and 1 ohm resisters in series till the gauge read E, 1/4, 1/2, 3/4 F in the car with the cars IVR and the cars wiring.

1755386191278.png


Great videos that explain how out gauges work

 
Bench testing I have done on water temp sender is as Dads Bee mentioned. I tested three senders and at around 70 degrees F, they all tested between 250-260 ohms
 
Last edited:
Sixpactogo said:
Bench testing I have done on water temp sender is as Dads Bee mentioned. I tested three senders and at around 70 degrees F, they all tested between 350-360 ohms
Click to expand...
Yep that's in the range I get too

1755523945793.png


dan juhasz said:
Where does 360 ohms fit in, I’m not following?
Click to expand...
The sender is a variable resister and has a very wide range that it can measure. Our gauges are only interested in the (roughly) 100 to 250 part of the range

So the sender that can read the interesting part of the range and can also read the other parts of the range BUT our gauges cannot.

Here is the curve that the sender CAN provide
1755524672282.png


Here is the PART of the senders range that the gauge CAN display
1755524739546.png


The gauge can only display this part of the entire curve

1755524913886.png


so when you measure the sender at room temperature it will read in the 300 ohms range till you heat it up to about the 135deg range, then it will be in the 73-10 range of its curve.
 
Dana67Dart said:
Yep that's in the range I get too

View attachment 1903811


The sender is a variable resister and has a very wide range that it can measure. Our gauges are only interested in the (roughly) 100 to 250 part of the range

So the sender that can read the interesting part of the range and can also read the other parts of the range BUT our gauges cannot.

Here is the curve that the sender CAN provide
View attachment 1903821

Here is the PART of the senders range that the gauge CAN display
View attachment 1903823

The gauge can only display this part of the entire curve

View attachment 1903829

so when you measure the sender at room temperature it will read in the 300 ohms range till you heat it up to about the 135deg range, then it will be in the 73-10 range of its curve.
Click to expand...
I bought a total of 5 senders before I came across one that measured around 400 ohms in 85 degree ambient temperature. That sender works and is accurate when checking with my thermal temp gun. It’s all about crap aftermarket parts nowadays. All the other senders measured between 120 to 200 ohms at the same ambient temperature. Those all showed between 230 and 250 degrees at idle with the true temp was about 175/180.
 
Often times the parts house will supply you with the wrong sender. It happened to me last year. In the picture, the sender on the left is new but bench tested at 500 ohms at room temp. (70F) The center one and the one on the right both read 352 and 360 respectively. I'm not sure what the part number is for the one on the left. It looks similar but has more threads and is not correct for a Mopar. The one on the right is a Standard TS-17.

100_1758.JPG


100_1759.JPG
 
Sixpactogo said:
Often times the parts house will supply you with the wrong sender. It happened to me last year. In the picture, the sender on the left is new but bench tested at 500 ohms at room temp. (70F) The center one and the one on the right both read 352 and 360 respectively. I'm not sure what the part number is for the one on the left. It looks similar but has more threads and is not correct for a Mopar. The one on the right is a Standard TS-17.

View attachment 1903897

View attachment 1903898
Click to expand...
I have a collection of ts17 and the economy ts17t. It’s like buying a moog lower control arm bushing, all wrong and unusable.
 
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