Serpentine/Accessory belt failure on a very wet, dark MI road in the middle of nowhere...

[Longtrail]

Are you sure the new ECT is giving you the reading on the left? That appears to be the hot side coolant temp sensor (coming out of the block), which should be at the back of the engine on the rear crossover. The ECT at the front of the engine (which I think is the one you replaced) is measuring the temperature of the coolant coming out of the radiator (cool side), which would be the lower number on the right. At least that’s my recollection.

In any case, those numbers look high if your engine was dead cold. If it was running even a minute or two, those temps might be correct (mine gets to full temp in about 5 minutes). Or, if you had been running it even a couple of hours before, it might be correct as it will retain heat for quite a while after shutting down.

"Are you sure the new ECT is giving you the reading on the left?"
Yes I think so, it's the same sensor that was previously complaining about a circuit issue. For some reason it seems to be measuring hot when it's not; the pipe wasn't even hot to the touch. Perhaps the wires are the wrong way around? Could somebody look to see if the yellow wire is connected to the left side of the plug as indicated below (image rotated for clarity)?

I hope it's yellow - I'm colorblind; the other color (red or green) is connected to the right pin, so like this (before I did the splice):

I will go record cold ignition on/engine off temps later on and will report back (like ftillier).

It is the front sensor, just below the thermostat that I replaced. The engine was cold, this was the first start of the day. The temperature on the dash is showing normal. When up to temperature I got these temps (swapped from previous positions):

Thank you so much for helping.

 

[ftillier]

What were your readings with ignition on/engine off? Did they look OK? The warm readings look good.

 

[Longtrail]

What were your readings with ignition on/engine off? Did they look OK? The warm readings look good.

I didn't read them yet, I was under the impression that I couldn't get the temps without the engine running! Will look once I'm free of meetings - Thank you.

 

[Longtrail]

I reread the temperatures, this is ignition on/engine off, initially I got this (which I suspect is why I aborted this the first time):

Rather than going to quick list I went to the full list and was able to read the following (the engine hasn't been started today):

I then realized I could get voltages as well (ouch!):

With engine running and the engine speed having dropped from initial high revs (so approx. a minute) I get this:

I plan to swap the cables as I think we've concluded (with the help of Range Rover) that their wrong... I had a 50/50 chance and blew it! Will report back.

 

[Longtrail]

Just to follow-up, with the cables swapped and a whole bunch of other experiments I still get the same readings... As ftillier points out, the temperature sensor is a thermistor which changes resistance with temperature; resistor type devices are typically not sensitive to direction of installation unlike say a diode... Anyway, it was worth a test! I plan to replace all the cooling hoses anyway, and when I get to this hose it comes with a new sensor which will give me something to test! FWIW the resistance I'm getting is about 2330 ohms this evening. The good thing is that this high temperature is not causing an engine fault; the bad thing is the sensor is there for a reason!... Will order the parts and follow-up but that's part of the much bigger project (timing chains and cooling system all at the same time).