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Temp gauge not working

Jm2576

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My temp gauge is not reading anything. I disconnected the wire to the sensor and connected it to a ground wire and the gauge read hot so I know the gauge itself is good. I replaced the sensor but the gauge still does not read anything.
 


alwaysFlOoReD

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Is the sensor one wire? It needs a good ground and of you wrap the threads with teflon tape that ground may not happen.
 

RonD

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+1 ^^^^ on the tape on the treads if its a one wire sender

Try pulling the connector again, if it is a 2 wire connector(red/white and black/white wires), then jumper the two wires together
Turn on the key, gauge should go to HOT
If not then the black/white wire is broken, no longer a ground

If gauge does go to HOT then they sold you the wrong or a broken SENDER
Sensors all run on 5volts or less and always at least 2 wires
Senders use 12volts and can be 1 or 2 wires
 

Sloryd66

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You didn’t mention either your trucks year or engine. On my 99 2.5L there’s actually 2 sensors…from what I learned, one is for the gauge and the other sends signal to the ecm on engine temp. My gauge always read low and I replaced the front sensor and it fixed it. If it’s a 2.5l they’re located in front of one another in the thermostat housing. The front nearest the radiator is the gauge one.
 

Jm2576

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Sorry for the lack of info...I was typing on my cell phone last night.
I have a 2000 Mazda B4000 4.0 v6
It looks like there are 2 sensors. The one in the front is the one I replaced, which has a single wire. I took it to the auto parts store to compare and make sure I had the right one and they looked exactly the same. I also jumped the wire to ground and the temp gauge read hot. I didn't use any teflon tape on it, but it did come with a small amount of red stuff at the top of the threads that I assume was some kind of anti-sieze compound.

I wonder if I have an air bubble in my coolant system, so I will try to purge it next. Is there any special purge valves I should know about, or do I just use a radiator funnel and run the engine & heater till the bubbles stop?

How should the gauge behave when it is working properly? I assume it will be on the low side when the engine is cold, but still register something once started? Mine is so far below the low side that I thought it was completely non-functional. Other vehicles I own that have a temp gauge, show way below the low side when the key is off, but the needle jumps up to the low/medium side once the key is on. Should my needle move at all when started?
 

RonD

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Yes the single wire Temp sender needs to have bare metal threads on the lower part only so the "red" stuff won't hurt anything
Sender needs to just have the one terminal if used on a one wire vehicle, if you see two terminals on sender then it won't work

Remove either Heater hose at the firewall and then refill at radiator, this will let all the air out of the engine side, so no air bubble
Coolant should run out of removed hose end and its heater core tube when all air is out, put hose back on and top up rad

For temp gauge Ford has 205degF as the 1/2 way point
Warmed up engine should be just below 1/2, 190degF

On cold start feel the heater hose and upper rad hose, should be same temp of course
Set cab control to Defrost, fan off or on low
Let engine idle for 2min
Feel both hoses again
Heater hose should be warming up
Upper rad hose should still be cold, no change
If upper rad hose is also warming up then thermostat is bad, stuck open
 

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