Overheating is one of the most common problems drivers experience with their cars. Not only is it an inconvenience to have to pull off the road with steam spewing from your hood, but overheating can also cause permanent engine damage or failure. Engines are designed to run at a specific temperature, which is called normal operating temperature. Overheating occurs when the engine exceeds normal operating temperature due to a malfunction within the cooling system.


The cooling system works by pumping coolant through the engine to absorb the heat created by the firing of the cylinders. The coolant then travels to the radiator where the heat is dissipated through the delicate fins and is pushed away from the radiator by the cooling fan. Because the system is relatively simple, there are generally three main causes of cooling system failure: lack of coolant, lack of pressure or flow, and an obstruction within the system.


The first cause, lack of coolant, can be easily identified by either a leak or an empty coolant recovery reservoir. If the reservoir is empty but there is no sign of a leak, remove the radiator cap to determine if there is coolant in the radiator. Be sure to only remove the radiator cap when the engine has been sitting and is cold. The cooling system is pressurized when the engine is running and personal injury can occur if the radiator cap is opened.


The second most common cause of cooling system problems is lack of pressure or flow within the cooling system. If this is the case, the most likely culprit is a stuck thermostat. The thermostat is designed to block coolant flow to the radiator until the engine has reached normal operating temperature. If the thermostat is stuck closed, coolant is cut off from the radiator and it will eventually begin to boil as the engine continues to run. The thermostat can be checked by squeezing the upper radiator hose with the engine running at normal operating temperature to feel if the coolant flowing through it to the radiator.


If the cooling system is not holding pressure, the most likely causes are a bad radiator cap or a bad water pump. A radiator cap is a cheap fix, and any repair shop should be able to pressure test your radiator cap or the entire cooling system should you so desire. A worn or loose water pump can also result in pressure loss because the pump is operating at less than it’s peak efficiency. This means that too little coolant is flowing through the system without enough pressure.


As coolant flows through the system, it passes through various tubes, hoses, and cooling jackets. It is not uncommon for a foreign object to become lodged in one of these components, causing an obstruction and blocking coolant flow. The cooling jackets and the radiator are the most common sites of blockages because these passages are relatively small and easily clogged by dirt or objects. A tube in the radiator can also become dented closed by an impact with an object on the road. The radiator is made of delicate aluminum that is easily bent and damaged.


An overheating problem should be diagnosed and fixed as soon as possible because catastrophic engine failure can result if it is ignored. As the engine rises above normal operating temperature, the oil begins to break down and lose it’s lubricating qualities. This can cause the engine to seize, which more often than not ruins the engine. Complete engine lockup is the worst possible result, but problems such as burnt valves and pistons are more common and happen much sooner.