my situation is i have a rebuilt 2.8 motor in an 89 Z that always runs at 220-260, once it gets to 260 my fan turns on and it goes back down to 220. BUT THEN IT GOES BACK UP TO 260! and back and forth. its been doing this for about 3 months and im worried im gonna fry my engine and be out alot of money.i have a new radiator and water pump, but thats all as far as the cooling system goes. does anyone have an idea on what could be the problem?