A faulty radiator cannot properly cool your car's engine. Radiators rely on thermodynamics to keep your engine from overheating, protecting your engine from damage.
Symptom
The most obvious symptom of a faulty radiator is overheating of your engine, readily apparent on your temperature gauge.
Causes
A faulty radiator and overheating of your engine can be caused by anything that obstructs your radiator's ability to gather hot fluid from your engine and pump it to the radiator where it can be cooled by air from the car's movement and the radiator's fan. This can be something as simple as a crack and leak in your radiator, allowing the fluid to flow out, or it can be a clogged tube within the radiator obstructing the flow of fluid, or it can be a broken fan.
Diagnosing the Problem
If your engine is overheating, first turn off your engine and check if your radiator needs fluid. Do not use your bare hand to open the radiator when the engine is overheating because it can easily burn you. Often, your radiator will simply need fluid. If your radiator has enough fluid, the problem is most likely obstruction of the fluid's circulation or a broken fan.
