Coolant Temperature Gauge Going Nuts Again

[NewLeSabreOwner]

Hi All,

Was looking for some input please. The Coolant Temperature Gauge on the dashboard is going nuts again. This time it does seemed at least a tad narrowed down compared to last time.

When the car is started from a overnight rest then the Temp Gauge goes all the way to the red and then back to the cold and dashboard reading from the odometer area goes from 100* to 240* in a fast count up and down over and over again, but then the lets say third time it goes from 110* to 240*, then the forth time 120* to 240* then finally when it gets around 140*ish it just stays there and then stops its chaos and climbs up slowly and then for the rest of the ride does not act up. Nor does it act up again, if the car is off for lets say 2 hours and turned back on. Only after an overnight rest does this seem to repeat itself. It only happens if I start the engine, if I just turn the key to the run area to light everything up, then it does not occur after an overnight rest.

This all seemed to start this time after the Air Filter was changed. I have already from last time gotten a new speedometer cluster. I tried replacing the PCM again, still occurred. I have replaced the coolant temperature sensor and it is still occurring. I squeezed the coolant lines maybe thinking there was an air bubble, didn't help. So my only thought at this point is it's either the wires or harness ( which look ok, didn't see any rust or rot) going from the coolant temp sensor or the wires going to the PCM that may have been moved a tad when replacing the filter while trying to get the air filter cover off. However, since I moved the wires to take off and put on the replacement PCM, I am not leaning towards that.

Any ideas? Thanks.

 

[HotZ28]

Do you have a capable scanner that can read ECT? If so, does it fluctuate like the gauge?

 

[NewLeSabreOwner]

Do you have a capable scanner that can read ECT? If so, does it fluctuate like the gauge?

Yep, I did not even think about that! Thank you!

The scanner did fluctuate like and with the gauge, I caught it on video this time and then she even stalled out on me near the end of the video. Then even after warming up some, she did it while driving as well for a good 5 minutes, then finally seemed to level out and not act up. Then I thought about it, put my scan tool up by the windshield and then popped the hood, and wiggled the coolant temperature sensor wires back and forth and the scan tool stayed steady without any fluctuations, so now im really not thinking its those wires or plug.

I am going to try to upload a video of it. Sorry I am not the best at technology, the video goes both ways and goes out of focus. I also could not get the scanner to get out of celsius either. But it still shows the large wiggles.

https://imgur.com/a/BYl8b03

 

[DrivenDaily]

I would be willing to guess that @HotZ28 was going to suggest that the ECT sensor needs to be replaced, and that you should first make sure that the connection to it is clean and secure before ordering a sensor.

But that's just a guess. I'll let him speak for himself.

Kudos on sharing the video. It tells a lot without words, and your description provides historic data that correlates.

 

[RD_Atlanta]

Since the issue shows up on the scanner live data (which was a good suggestion), I would think the problem must be in the ECT sensor, the PCM or the short length of wire in-between (or at one of 3 the electrical connectors. Have a look at the attached PDF which hopefully will help. If you have an ohm meter and a couple of test probes/test clips, I think that you can spend a little time checking the integrity of both the ECT sensor and the short electrical path to the PCM (blue & clear connectors). Really focus on the visual health appearance of the pins in the connectors with a bright light. The problem being somewhere in this area is 'possibly' collaborated by your telling us that the problem did not occur until the air filter was replaced (which happens to be where the PCM, PCM connectors & PCM wire harnesses are physically located).

If after checking the circuit with an ohm meter does not reveal the root cause, one thing to consider is use some insulation piercing test clips with your multimeter and monitor the sensor circuit voltage with a digital multimeter. This way you can monitor the same voltage that the PCM A-to-D converter is seeing when starting after the LeSabre has sat overnight. Then insulate the test leads after the test. The good news is this is a very short & easy to access circuit.