tstill

Hi,
I own a 97 Mercury Mystique GS with a 2 liter Zetec engine. I love this car. But after two years it has finally had it's first problem. I had to replace the water pump, timing belt and timing belt tensioner. The water pump failed causing the engine to overheat and then shut off by itself. On inspection I found the plastic portion of the timing belt tensioner had cracked into three pieces. After replacing these parts it ran fine just like before. I noticed afterwards that the temprature gauge tended to veer towards the hot side and the fan was not kicking in when I thought it should. I had the coolant temprature sensor tested at AutoZone and they said it should be replaced. I replaced it and the car would NOT start. I put the old sensor back in but it still wouldn't start. I took it to a nearby mechanic and he said it needed a new "cylinder head temprature sensor". $130.00 later it had a new one and it runs fine now but still on the hot side. The mechanic explained that the ECU is programmed to kick on the fan at 200 degrees and that the heat would not hurt anything but if I felt compelled to make it run cooler install a cooler thermostat.
I can't find anything in my service manual or on the internet about this cylinder head temprature sensor. Is there such a thing or did I get screwed?