Chrysler Repair: Running hot, coolant temperature sensor, thermostat temperature

Question
I have a 1992 Plymouth Acclaim 2.5L 4cyl 214k miles. I have just recently aqquired this car from a good friend and to go into a lot of detail first off the heater core was bypassed b4 I got the car the temp on it was doing fine(it has a guage instead of light)staying down near the Cold end of the normal range. just recently it has been showing that it is running hot by the guage I have replaced the thermostat, temperature sensor, and as of yesterday the coolant temperature sensor. I have asked one person at an autozone about it and he said i could run the A/c for now til I could find out what is going on but with no heat it gets very cold i am also not showing signs of leakage or steam anywhere. the Fan now will sometimes come on at the very high side of the normail range or sometimes just at or above hot, and i am afraid that something is going to blow on this car.

Answer
Hi Richard,
I believe that your problem may be due to there being air trapped in your cooling system (the heater core and the theromstat housing are the most likely areas of entrapment).
There is a very specific procedure that must be followed to drain and refill the system or you run the risk of getting air trapped which causes the thermostat to falsely open at too high a temperature. let me run through the details that are peculiar to the
> Chrysler 4-cyl engines. There is a plug in the top of the thermostat
> housing (8mm allen head) that has to be considered when you are
> dealing with the cooling system or you will trap air in the housing or
> the heater. Here is the way to do drain and refill:
> Start the engine and put the heater control slider in the Heat
> position (this opens the water line to the heater). (A/C should be off
> of course)
> Shut off the engine
> Open the radiator drain valve and watch to see that the water drains
> first from the coolant recovery bottle. Then remove the radiator cap
> and let about another quart or so drain out. (You can collect the
> coolant in a pan for reuse if you choose).
> Then remove the plug from the top of the thermostat housing and let
> the water drain out of that housing, use a flashlight to observe level
> (you don't have to drain any further if you are just trying to remove
> trapped air, otherwise complete draining).
> Close the drain.
> Start refilling thru the radiator cap opening
> When the coolant level rises into the thermostat housing and up to the
> top of the plug hole, stop filling and put in the plug (put some
> never-seize compound on the plug threads).
> Continue filling thru the radiator cap opening until radiator is full.
> Put on radiator cap.
> Fill the coolant recovery bottle to the "max" line on the bottle.
> In theory you will have now a air free cooling system. At least if
> there is any trapped air it will work its way out more quickly if you
> follow this procedure exactly. This may lower your operating
> temperature and also eliminate the intial rapid rise of the gauge.
So I would suggest that you go thru this procedure. If you collect the coolant you can reuse it. Then let me know if this doesn't solve your problem.
Roland