Showing it's getting hot ??

I have a 05 Buick Rendezvous ,when the fans kick on the temperature gauge goes up to about 3/4 then when the fans kick off temperature gauge goes back down to about 1/4 ? Not sure what the problem is ? took it to have a diagnostic test done on it and it’s showing that the motor is not getting hot at all ,it’s at 216 , what it calls for , only other problem that showed up on the diagnostic test was the oil sensor,
also having problems getting the vehicle to start , doesn't want to start without giving it a little bit of fuel ? then it starts up? Parts replaced so far, A new Thermostat , A new temperature sensor , Fuel Injector ,Idle Control Valve ,Throttle Position Sensor . Please help !