Strange problem, don't know where to start

I will fire up the jeep cold, no problem. Bare in mind I have to prime it (internal fuel leak). But, for me, nothing out of the ordinary.

Once it reaches warm running temp (around 200), temp gauge drops instantly to zero, idle gets up to about 1100rpm, and if I shut it off, and start it hot, (even with priming again) she has a very hard time starting. Usually been getting it to fire up by flooring it when turning it over.

But, once running again, other than high idle, it runs fine, no power loss. Any ideas? Im baffled. Maybe evap circuit or solenoid? I don't know what else changes right at 200 degrees....

Could be your coolant temp sensor opening up. At 200 degrees read the sensor with an ohmeter. It should register a few hundred ohms. If it reads K ohms, megohms, or open circuit the sensor is bad. Also, clean up the sensor and pigtail terminals making sure nothing is loose, dirty, corroded etc

OK got to looking at this. Of coarse, when you WANT something to go wrong, it does not... I got the engine up to temp and for the first time in a while, it held the 210 mark, nothing funky.

Regardless, I checked the resistance across the temp sensor using a digital multi-meter, I have found that the resistance will show mid 100's quickly, then went open circuit. I have tried this several times, hot and cold, seems to react the same.

Would this be an effect of using a digital meter, rather than analog meter? And, am I measuring the right sensor (see pic below)

Could be the probes giving the intermittent continuity. If you dont have aligator clips, I would clean up the connections and see if the problem goes away after confirming that the gauge or RPM does not change with a wiggle test.

The image was just for reference, I was getting good contact on the connector no doubt. The instant result followed by the open circuit reading was consistent.

I cleaned the contactors best I could, and took the jeep for another spin. Again, it ran perfectly fine. We'll see what happens tomorrow..

http://i266.photobucket.com/albums/ii244/AHhub/forum stuff/Resistancetable.png

Were you trying to test the sensor on the 200 Ohm range?

You have the meter on the wrong range, use 2000 not 200 ohm range. Also it is more likely to be a problem with the air charge temp sensor, also called a manifold air temperature sensor, that a coolant temp sensor problem for starting problems. What year is it?

It's 97. Ever since I cleaned the contractors on the coolant temp sensor it has not done this. Must have got loose or dirty over time? I will keep an eye on it though, and check in the 2000 range!

I think coolant sensor is the culprit here because of the additional symptom of the coolant temp gauge on the dash also dropping at the exact same time.

If it comes back, don't mess around any more; just buy a new sensor.