Coolant temperature gauge does not work

fleming442

Captain Tenneal
Supporting Member
Dec 26, 2013
12,489
113
Test for continuity from the sensor body to both terminals. Then, test for continuity across the 2 sensor terminals. Then, test the 2 terminals as the engine warms up.

By polarity I mean that the sensor is isolated from the body, allowing it to be used for 12v instead of ground. Your light/gauge wires should both need ground. If neither terminal has continuity to the sensor body, you need to ground one of the terminals to make the sensor work.
 

fly_25

Not-quite-so-new-guy
Thread starter
Oct 20, 2020
31
8
There is no continuity between either terminal and the housing (ground), but 6000 ohms at cold between the terminals. if one terminal needs to be ground, does that mean both the light wire and gauge wire needs to be connected to the same terminal?
 

fleming442

Captain Tenneal
Supporting Member
Dec 26, 2013
12,489
113
There is no continuity between either terminal and the housing (ground), but 6000 ohms at cold between the terminals. if one terminal needs to be ground, does that mean both the light wire and gauge wire needs to be connected to the same terminal?
I don't think I've ever seen them tied together. My best guess is ground one terminal, then figure out which wire goes to that sender. Then, get another sender for the remaining wire.

Ain't interwebz troubleshootins' fun?!?! NOT!!!!
 
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5spdCab

G-Body Guru
Dec 29, 2019
834
93
Tukwila, Wa.
All of that makes sense, what has me confused is that the gauge doesn`t move at all when both wires are hooked up to the "correct" style of sensor, but the gauge does move when only one wire (the one that maxes out the gauge when grounded) is connected to the single blade style sensor, leaving the other wire (the one that turns the light on when grounded) disconnected. I am also getting 12v at each wire coming from the car. The coolant light has all the wiring hooked up and all, and it does operate when that wire is grounded. If one wire is for the gauge and the other wire is for the light (in the case of there being another sensor somewhere), why does the sensor have 2 terminals? I don`t see a third wire anywhere for the second gauge sensor terminal
12v on both wires is a good sign. That means that both are connected to the instrument cluster. Could it be that the sensor is a daul function? The semi truck that I drive has temp gauge, but also a warning light/buzzer combination, though I do not know if it uses one dual function or two single function units.
My only other thought, and I would have to go back to the beginning of this thread, does the engine run, and does it have the coolant topped off? If both answers are "yes", try another sending unit again, in case the current one is the wrong type.
 

LeftLaneOnly

Apprentice
Mar 20, 2020
63
33
Is the car getting over heated?? does it spit coolant after you shut it down when its pegged to hot..
if not my guess the cluster needs to be pulled and cleaned up. there are a few threads showing how to do this.
Also happens to be my next project on the Bad Martha
 

fly_25

Not-quite-so-new-guy
Thread starter
Oct 20, 2020
31
8
Cluster has a new printed circuit board because the old one was all ripped up, everything works in the cluster, even the lights! Engine doesn't seem to overheat, no spilled coolant or anything and the thermostat does open so I think the actual engine temp is okay. I think it must be I'm not connecting the right wires to the right sensor
 
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LeftLaneOnly

Apprentice
Mar 20, 2020
63
33
Did you clean up the connections on the temp gauge itself ( has to be removed from cluster) when you replaced the circuit board
 

fly_25

Not-quite-so-new-guy
Thread starter
Oct 20, 2020
31
8
I did not clean the connectors but they did look to be okay, worth a shot to clean them. I installed a single blade sensor for a gauge and it currently reads 10k ohms, and the "correct" sensor I have with the 2 terminals reads 8k ohms, at -5 degrees C
 

fly_25

Not-quite-so-new-guy
Thread starter
Oct 20, 2020
31
8
Sensor with the 2 terminals reads 380 ohms at 75 degrees Celsius between the 2 terminals, but still no continuity to the house (ground). If I have a wire for the gauge and a wire for the light, it must be the wrong sensor
 
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