Chrysler Repair: 97 T & C: coolant from overflow bottle, with no fan action, head gasket leak, coolant temp

Question
I have a 97 Town and Country minivan, when i plug in the coolant sensor, the fan does not kick on. The water from the coolant bottle keeps coming back up. If I unplug the coolant sensor, then the fan kick on. Can you give me an advice on what this problem might be?

Answer
Hi John
It may be that the coolant temp sensor is off value and under estimating the temperature of the coolant. It should read 700-1000 ohms when the engine is at operating temperature. So use an ohm meter across its terminals to see what that shows when the temp gauge shows about half scale. If it reads closer to 1500-2000 ohms then it is clearly under estimating the temp. The engine computer is programmed to turn on the fan if you disconnect the sensor so that is normal.
Another possibility is that the engine isn't really needing the fans but instead that water coming from the coolant bottle is doing so because the system is being falsely pressurized due to a head gasket leak. That would be the case if this coolant comes out the bottle fairly quickly after starting the engine and if the temperature of the coolant is not boiling. Another sign of a head gasket leak would be excessive white smoke coming from the tailpipe when you first start the engine from cold and also you might also see cloudy/milky engine oil on the dip stick. So I would suggest that you assess for this possibility also.
Roland
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