Question: how to tell if your radiator is on?
Answer: Leaking coolant onto the floor. The coolant flows through the radiator, so if there is a leak in the radiator, coolant will leak onto the floor underneath the vehicle. ... 
Vehicle overheats. If your vehicle is constantly overheating, the radiator may be going bad. ... 
Sludge in the radiator. ... 
Low coolant.