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Resistance specs on coolant temp senders? #3052541
06/22/22 08:32 PM
06/22/22 08:32 PM
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So I have my original sender from the 74, reads 244 ohms at room temp. I installed it with the 93 wiring and gauge cluster and the temp gauge reads about 1/4 not running at room tempature. No coolant and hasn't run in a month. So I figured I needed a newer sensor, got one spec'd for an 89 and it reads 196 ohms at room temp. Gauge reads about halfway, same conditions as before. After much ado I found one for the 93, what a PITA, anyway it will interfere with my fuel line so I'd rather not use it. If I knew the specs I could just add a resistor in line to rectify the condition. So any one got specs on those senders?


I raise chickens, so I am literally a chicken tender.

The Scamp is sold, now just two old trucks and one new one.
'92 D250 Club Cab CTD, 47RH conversion, pump tweaks, injectors, rear disc and hydroboost conversion.
'74 W200 Crew Cab 360, NV4500, D44, D60 and NP205 divorced transfer case.
2019 1500 Long Horn Crew Cab 4WD, 5.7 Hemi.
Re: Resistance specs on coolant temp senders? [Re: Guitar Jones] #3052543
06/22/22 08:34 PM
06/22/22 08:34 PM
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For a gauge, the resistance varies with temperature. So just adding a resistor inline isn't likely to fix the issue.

As for the rest of what you were saying, I am confused.

Re: Resistance specs on coolant temp senders? [Re: Sniper] #3052592
06/23/22 12:38 AM
06/23/22 12:38 AM
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I know it varies, I have two identical senders, one measures 244 ohms, the other measures 196 ohms, cold, no coolant. The 244 ohm unit registers about 1/4 on the temp gauge, the 196 ohm unit registers about half way on the gauge. Engine not running, hasn't been run for a month and no coolant in the engine, just key on.
Aftermarket shows the same sender for my 74 and an 89 model year.
The gauge, cluster and wiring all came from a 93 Ram Charger 5.2 magnum. That used a different sender with a different connector. It's taller and the connector would interfere with my fuel line to the carb. I don't have one to measure its resistance. So I'm trying to figure out what the senders resistance should be at X temperature and if the early senders ohm readings are different from the later magnum engines.
It looks to me like around 300 ohms would register cold on the gauge and as the engine warmed up the resistance would go down and the temp gauge would go up.
If that isn't correct then I have another problem like a ground issue or something.


I raise chickens, so I am literally a chicken tender.

The Scamp is sold, now just two old trucks and one new one.
'92 D250 Club Cab CTD, 47RH conversion, pump tweaks, injectors, rear disc and hydroboost conversion.
'74 W200 Crew Cab 360, NV4500, D44, D60 and NP205 divorced transfer case.
2019 1500 Long Horn Crew Cab 4WD, 5.7 Hemi.
Re: Resistance specs on coolant temp senders? [Re: Guitar Jones] #3052595
06/23/22 02:49 AM
06/23/22 02:49 AM
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This thread says the sender should read between 300-350 ohms at 70 degrees which would correspond with what I'm thinking would get my gauge to read properly. 3rd post in thread.
FBBO thread


I raise chickens, so I am literally a chicken tender.

The Scamp is sold, now just two old trucks and one new one.
'92 D250 Club Cab CTD, 47RH conversion, pump tweaks, injectors, rear disc and hydroboost conversion.
'74 W200 Crew Cab 360, NV4500, D44, D60 and NP205 divorced transfer case.
2019 1500 Long Horn Crew Cab 4WD, 5.7 Hemi.
Re: Resistance specs on coolant temp senders? [Re: Guitar Jones] #3052611
06/23/22 08:45 AM
06/23/22 08:45 AM
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I just looked in the '73 service manual and it reads the same as the earlier ones. The tool to test the stock temperature gauge is C-3826 which has a resistance of 73 ohms to mimic the minimum scale reading and 9.6 ohms which mimics the temperature gauge full scale.


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Re: Resistance specs on coolant temp senders? [Re: Guitar Jones] #3052612
06/23/22 08:46 AM
06/23/22 08:46 AM
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Mopar used to make a tester box for verifying the gauges, works on all the gauges, temp, pressure, fuel but not the ammeter.

L = 73.7 Ohms (empty)
M = 23.0 Ohms (1/2)
H = 10.2 Ohms (full)

Not sure where that 300 ohms claim comes from, not true for a 74 and you have to match the sender to the gauge, not the engine

Re: Resistance specs on coolant temp senders? [Re: 6PakBee] #3052613
06/23/22 08:48 AM
06/23/22 08:48 AM
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That sounds like a fuel gauge spec. I've got a 77 and a 93 FSM but haven't found a spec for the temp gauge in them.


I raise chickens, so I am literally a chicken tender.

The Scamp is sold, now just two old trucks and one new one.
'92 D250 Club Cab CTD, 47RH conversion, pump tweaks, injectors, rear disc and hydroboost conversion.
'74 W200 Crew Cab 360, NV4500, D44, D60 and NP205 divorced transfer case.
2019 1500 Long Horn Crew Cab 4WD, 5.7 Hemi.
Re: Resistance specs on coolant temp senders? [Re: Guitar Jones] #3052616
06/23/22 08:51 AM
06/23/22 08:51 AM
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Originally Posted by Guitar Jones
That sounds like a fuel gauge spec. I've got a 77 and a 93 FSM but haven't found a spec for the temp gauge in them.


As I stated, they are the same FOR ALL GAUGES, fuel included, excepting the ammeter. The specific tester Mopar used back in the day tested all the gauges with the same values.

The tester is Mopar C-3826 here's a pdf on it's function

https://www.mymopar.com/downloads/mtsc/155.pdf

Here's the film strip

https://mymopar.com/mtsc-1960-volume-13-11-instrument-panel-service/

Re: Resistance specs on coolant temp senders? [Re: Guitar Jones] #3052627
06/23/22 09:36 AM
06/23/22 09:36 AM
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Originally Posted by Guitar Jones
That sounds like a fuel gauge spec. I've got a 77 and a 93 FSM but haven't found a spec for the temp gauge in them.


on a 1993
are there 2 coolant temperature sensors on either side of the thermostat pipe nipple,
one for working the dash gauge
and one for the PCM using the “common” 5 volt supply ?

1994-1995 OBD-I Magnum V8s had 2 sensors.
1996+ I think changed yet again.

1992-1993 5.2 Magnum V8s I do not know.

Re: Resistance specs on coolant temp senders? [Re: Sniper] #3052639
06/23/22 10:00 AM
06/23/22 10:00 AM
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None of those values make sense. The values of 244 and 196 ohms are what I am reading directly on the two senders I have. Lower readings would make the gauge read even higher. I've used that tester many decades ago on fuel gauges but don't ever remember using it on a temp gauge.


I raise chickens, so I am literally a chicken tender.

The Scamp is sold, now just two old trucks and one new one.
'92 D250 Club Cab CTD, 47RH conversion, pump tweaks, injectors, rear disc and hydroboost conversion.
'74 W200 Crew Cab 360, NV4500, D44, D60 and NP205 divorced transfer case.
2019 1500 Long Horn Crew Cab 4WD, 5.7 Hemi.
Re: Resistance specs on coolant temp senders? [Re: 360view] #3052643
06/23/22 10:03 AM
06/23/22 10:03 AM
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Guitar Jones Offline OP
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Yes it has two. A sensor for the PCM (2 pins) and a sender for the gauge (1 pin). That is why I didn't think the gauge would have changed for the last two years of production.


I raise chickens, so I am literally a chicken tender.

The Scamp is sold, now just two old trucks and one new one.
'92 D250 Club Cab CTD, 47RH conversion, pump tweaks, injectors, rear disc and hydroboost conversion.
'74 W200 Crew Cab 360, NV4500, D44, D60 and NP205 divorced transfer case.
2019 1500 Long Horn Crew Cab 4WD, 5.7 Hemi.
Re: Resistance specs on coolant temp senders? [Re: Sniper] #3052657
06/23/22 10:27 AM
06/23/22 10:27 AM
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in a cattle trailer down by th...
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Guitar Jones Offline OP
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Just found this in the 93 FSM.
Temperature gauge
Cold graduation 655 ohms
Hot graduation 64 ohms
Fuel gauge
Empty 90 ohms
Full 12 ohms
Oil pressure gauge
Low 100 ohms
High 12 ohms.

So neither of the senders I have come close to the spec. for the 93. Going to look through my 77 manual now.



I raise chickens, so I am literally a chicken tender.

The Scamp is sold, now just two old trucks and one new one.
'92 D250 Club Cab CTD, 47RH conversion, pump tweaks, injectors, rear disc and hydroboost conversion.
'74 W200 Crew Cab 360, NV4500, D44, D60 and NP205 divorced transfer case.
2019 1500 Long Horn Crew Cab 4WD, 5.7 Hemi.
Re: Resistance specs on coolant temp senders? [Re: Guitar Jones] #3052669
06/23/22 10:47 AM
06/23/22 10:47 AM
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No such spec in the 77 FSM.


I raise chickens, so I am literally a chicken tender.

The Scamp is sold, now just two old trucks and one new one.
'92 D250 Club Cab CTD, 47RH conversion, pump tweaks, injectors, rear disc and hydroboost conversion.
'74 W200 Crew Cab 360, NV4500, D44, D60 and NP205 divorced transfer case.
2019 1500 Long Horn Crew Cab 4WD, 5.7 Hemi.
Re: Resistance specs on coolant temp senders? [Re: Guitar Jones] #3052681
06/23/22 11:16 AM
06/23/22 11:16 AM
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Originally Posted by Guitar Jones
That sounds like a fuel gauge spec. I've got a 77 and a 93 FSM but haven't found a spec for the temp gauge in them.

Attached PDF document
Temperature Test.pdf (10 downloads)

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Re: Resistance specs on coolant temp senders? [Re: 6PakBee] #3052682
06/23/22 11:26 AM
06/23/22 11:26 AM
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Yes, I know all about that, I'm trying to explain to you guys that those values don't match what I'm measuring. That is a very old tool, probably from the 40s and I'm not sure as to what years it was useful for. Please see the specs I posted from the 93 FSM.


I raise chickens, so I am literally a chicken tender.

The Scamp is sold, now just two old trucks and one new one.
'92 D250 Club Cab CTD, 47RH conversion, pump tweaks, injectors, rear disc and hydroboost conversion.
'74 W200 Crew Cab 360, NV4500, D44, D60 and NP205 divorced transfer case.
2019 1500 Long Horn Crew Cab 4WD, 5.7 Hemi.
Re: Resistance specs on coolant temp senders? [Re: Guitar Jones] #3052715
06/23/22 01:49 PM
06/23/22 01:49 PM
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in a cattle trailer down by th...
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Guitar Jones Offline OP
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from the 93 FSM, sideways laugh2

20220623_134048.jpg

I raise chickens, so I am literally a chicken tender.

The Scamp is sold, now just two old trucks and one new one.
'92 D250 Club Cab CTD, 47RH conversion, pump tweaks, injectors, rear disc and hydroboost conversion.
'74 W200 Crew Cab 360, NV4500, D44, D60 and NP205 divorced transfer case.
2019 1500 Long Horn Crew Cab 4WD, 5.7 Hemi.
Re: Resistance specs on coolant temp senders? [Re: Guitar Jones] #3052722
06/23/22 02:20 PM
06/23/22 02:20 PM
Joined: Jan 2003
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The C-3826 may be old but it was used for decades as long as the thermal gauges were in use. Based on my 78-81 truck parts book from Mymopar, as late as '78 the IVR was PN 3592899 which superseded PN 2258413 which is the IVR for the thermal gauges that C-3826 was used to test since the early '60's. Bottom line, I think the C-3826 tool is still the tool to use on your '74 and the 244 ohm sender you have is not the stock sender for a '74 Mopar. The values from the '93 FSM are not applicable as Mopar had stopped using thermal gauges by then.


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Re: Resistance specs on coolant temp senders? [Re: 6PakBee] #3052726
06/23/22 02:30 PM
06/23/22 02:30 PM
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Originally Posted by 6PakBee
The C-3826 may be old but it was used for decades as long as the thermal gauges were in use. Based on my 78-81 truck parts book from Mymopar, as late as '78 the IVR was PN 3592899 which superseded PN 2258413 which is the IVR for the thermal gauges that C-3826 was used to test since the early '60's. Bottom line, I think the C-3826 tool is still the tool to use on your '74 and the 244 ohm sender you have is not the stock sender for a '74 Mopar. The values from the '93 FSM are not applicable as Mopar had stopped using thermal gauges by then.


He said he is running the 93 cluster and wiring. Magnums had two temperature sensors one for the gauge and one for the computer.

Re: Resistance specs on coolant temp senders? [Re: NITROUSN] #3052745
06/23/22 03:26 PM
06/23/22 03:26 PM
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Originally Posted by NITROUSN
Originally Posted by 6PakBee
The C-3826 may be old but it was used for decades as long as the thermal gauges were in use. Based on my 78-81 truck parts book from Mymopar, as late as '78 the IVR was PN 3592899 which superseded PN 2258413 which is the IVR for the thermal gauges that C-3826 was used to test since the early '60's. Bottom line, I think the C-3826 tool is still the tool to use on your '74 and the 244 ohm sender you have is not the stock sender for a '74 Mopar. The values from the '93 FSM are not applicable as Mopar had stopped using thermal gauges by then.


He said he is running the 93 cluster and wiring. Magnums had two temperature sensors one for the gauge and one for the computer.

All correct, which is why I thought the 89 sender (196 ohm unit) would work as it looks just like the early units and clears my fuel line, but I guess I was wrong. laugh2 Not the first time and certainly won't be the last.


I raise chickens, so I am literally a chicken tender.

The Scamp is sold, now just two old trucks and one new one.
'92 D250 Club Cab CTD, 47RH conversion, pump tweaks, injectors, rear disc and hydroboost conversion.
'74 W200 Crew Cab 360, NV4500, D44, D60 and NP205 divorced transfer case.
2019 1500 Long Horn Crew Cab 4WD, 5.7 Hemi.
Re: Resistance specs on coolant temp senders? [Re: Guitar Jones] #3052753
06/23/22 03:44 PM
06/23/22 03:44 PM
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out of curiosity, is the bulb portion of the sender that goes into the coolant flow shiny brass color, or is it discolored to a greenish tint ?
beer

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