Coolant temp readings are off

[TSIkw]

My coolant temp readings have been all over the place lately. It was reading fine one day then it slowly starting reading lower and lower temps...down around 125. Then it dropped to -40.

I put a new sensor and thermostat (192 degree) in to be safe. It seemed ok for a bit then next thing i knew it was at -40 again.

I tested the resistance of the sensor today according to my instruction manual.

Cold Reading: 1200-1500 ohms
Warm Reading: 277 ohms

Manual says it should be...
Cold Reading: 2200-2500 ohms
Warm Reading: 280-320 ohms

I also tested the voltage on the wires and they are fine...4.6 volts.

What would these resistance readings mean? The resistance when the engine was cold is low but when its warm it was just about in range.

Just idling today the temps eventually got up to 190 but it came back down and stayed around 176. I don't think that is warm enough to get my fuel trims to adjust.

 

[oldman]

I had the same problem last year and it turned out that the amount of heat in that area has harden the signal wires causing copper inside the wire to break even though it looks ok from outside making my connection intermittent at best. I cut both wires further upstream (about 5") and soldered new wires up to the sensor and the problem was solved.

 

[TSIkw]

I did that with the wire last summer. I just took it for a drive and it was fine. Running between 193 and 200. But yesterday it was all off. Maybe the wires are bad like you mentioned and its working intermittently.

When i did the voltage test on the wire I had to get the probes just right on the connectors to get a good signal.