Engine Coolant Temperature Sensor

I have a 98 XJ 4.0, Auto. I recently had the check engine light coem on, got the code, etc. Code said the sensor was giving a low voltage condition, so
I replaced the sensor and it was fine for about 3 days. Then I got the code again for the same problem, but it went away within a day. Again it stayed off for a few days, and now its back on again last night. The only thing I see happening when it turns back on (the idiot light) is that my temp. guage drops from normal operating temp down to around 100 then goes back up again. I've checked the connections and will be hosing it down with component cleaner again during lunch break. Any suggestions what else might be causing this?

A bad ground ?Did you use any tape or sealant on the sensor when installing ?
Wayne

Other than the thread sealant on the sensor itself, no. There was none on the old one either. And the part is straight from a dealer, not a parts shop, so its exact fit.

You probably don,t want to drain the rad and all,but doing that and cleaning the threads in the housing would eliminate a possible problem area.
Wayne

had same problem fixed it by cleaning the threads on the housing and I had a wire that looked like it was pinched so i replaced it, no problems since

As in cleaning off the old thread sealant that is probably in the housing from the old sensor? Worth a try, I suppose... Can teflon tape be used to seal it back up later if what is left on the sensor itself isn't sufficient?

old sealant, corrosion anything other than whats supposed to be there.

The problem with self-grounding sensors is that if you keep it from contacting metal, it won't work.

I've had good luck using SMALL amounts of RTV copper (no other variation) - since it was designed for use with self-grounding sensors. I do mean small - I only put it on about two threads, and let it get all smeared out.

There was probably nothing on the original sensor - both due to it being self-grounding, and the innate cheapness of mass production (save ten cents over a production life of two million, and you're getting somewhere...)

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