"Coolant Sensor Bad"

Hi All,
I have a 1997 Jeep Grand Cherokee Laredo 4x4. For the last year or so, every so often (a few times a week), I get the message "Coolant Sensor
Bad" in the center console (the area that shows "miles to service" and when doors are open and such). According to various sources, the coolant sensor in question is the coolant level sensor in the overflow tank. The other coolant sensor that is in the engine block throws a "check engine light" error code if it's having problems (I've verified that by unplugging it), so I'm reasonably certain that that's not the one causing the problem.
Now, I'm sure most of you are thinking, "why don't you just replace the coolant level sensor?" I did that right away last year when it first started happening. It didn't have any affect on the problem whatsoever. I've also brought the car to the Jeep dealer, and surprise, surprise, it didn't happen while the car was there, so I got to pay the diagnostic fee and go home.
One interesting thing is that the "coolant sensor bad" message didn't occur all winter, so it does appear to be affected--at least to some degree--by temperature.
Anybody have any ideas on how either to fix the problem with the coolant sensor, or to at least get it to stop telling me about it? I don't particularly care if there's a problem with the coolant level sensor...I'm perfectly capable of lifting the hood to look at the overflow tank, but the beeping from the console is kind of annoying.
Thanks, Tom
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IS there a layer of brownish red scum (or any other color) in the expansion tank?

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No, but there was back when I bought the car. I flushed the coolant using one of those garden-hose adapter things, and cleaned the overflow tank about two years ago. I wouldn't eat off of it or anything now, but it's reasonably clean.
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Have you tried unplugging the neg battery cable for 30 mins to re set the computer?
Carl

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snipped-for-privacy@gersic.com proclaimed:

Connectors on the wiring to that sensor all crudded up?
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The girl that owned the WJ before me allowed her quickie-lube to add Prestone Universal (DexCool) to the system.
It turned the coolant into brownish red sludge
The sensor is pretty much a float but the float gets stuck when it is full of sludge.
proclaimed:

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I would start by cleaning the plug and socket on it with a good spray contact cleaner.
Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Jan/06 http://www.imagestation.com/album/pictures.html?id !15147590 (More Off Road album links at bottom of the view page)
snipped-for-privacy@gersic.com wrote:

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