i was talkin about these today and aparently they will give you an incorrect reading of engine temprature, but will give you a reading of water temp going through your radiator...
i was told for a accurate reading to put the temp sensor as close as you can to the heads, get a custom made t-piece to accomidate both factory and aftermarket unit or, in some cars there are bungs put in from the factory where they may have planned to put something there or for some other reason unknown...
but i think i will be happy to put the piece on the top radiator hose. temp there will be close enough to the heat made by/in the heads.
my bit
4dftn