The auxilary fan in my 89 300TE has been operating erratically. It generally performs the desired function of kicking in above 100 and continuing to run until the engine cools - but it also kicks in at 40 and 80! When it does this, it turns on and off over 5 second intervals. Is this a faulty temp sensor? - how can it be fixed?

Thanks, as always, for your input.