Thermostat Stuck Shut The thermostat is generally placed in housing where the upper radiator hose joins the engine, manages the working heat of the engine. It is done by blocking the flood of coolant from the engine to the radiator. It keeps the process working until the engine arrives at a positive heat. When this heat reaches the thermostat releases and permits coolant to have a flow from the engine to the radiator. If the thermostat remains unable to release because of the mechanical failure or any other reason, no coolant will move between the radiator and engine, and the engine will automatically get overheated. You can easily confirm this condition with a single touch to the upper radiator hose. If the upper radiator hose is not heated even after several minutes of starting the engine, it signifies that thermostat is surely having some faults and needs to be replaced. Inoperative Fan Motor The fan that gives air to the radiator is forced through an electric motor in most front-wheel drive cars. A coolant sensor or temperature switch on the engine sets the fan on and off when extra cooling is required. If the coolant sensor, the fan motor or temperature switch is not working properly, the fan would fail to air when it is required. If you are feeling such kind of problem, you must take your vehicle to be checked by experienced mechanic. Defective Fan Clutch The "fan clutch" with belt-driven cooling fan is usually used to develop the economy of the fuel for rear wheel drive vehicles. The clutch is a sticky-combination blocked with silicone oil. The clutch permits the fan to fall at lofty speed, which decreases the continuous horsepower pull on the engine. The fan may not rotate fast to remain the engine cool, if in any case the clutch fails to slips. The silicone fluid within the clutch can break down or can leak out due to wear. If you see greasy strips radiating external on the clutch, it means the clutch needs to be replaced. Internal Coolant Leak If no coolant leaks are noticeable but the engine is using coolant, your cylinder head may have a crack or it may be blocked that is causing coolant to flee into the crankcase or combustion chamber. Leaky or Weak Radiator Cap If no leaks are noticeable, you must check the radiator cap to ensure that it is keeping a certain pressure. The engine will get hot and will lose coolant out the flood tube consistently, if the spring inside the cap is weak. Bad Water Pump The impeller of the high mileage engine that powers the coolant through the engine within the water pump can be a reason of overheating the engine. Its blades can be loose or totally decayed.  If you are facing such problems, the pump should be replaced.