if it goes into the red I wouldn't recommend driving it until that problem is fixed as a $100 problem can end up being a $2000 one if the radiator was full before you overheated it as when a car overheats coolant is pushed out fills the overflow then onto the ground if the fans didn't come on I would guess the fan switch ,or bad fans (check by turning a/c on) or thermostat ..the thermostat and fans switch are pretty cheep and a easy DIY job and recommended if the car got hot because they can be damaged from overheating ..