When we talk about a vehicle overheating, it's worth having a basic understanding of how an automotive cooling system works. The heart of the system is the engine and the coolant, which is a liquid mixture of water and concentrated coolant/antifreeze. This mixture will not boil at high temperatures, or freeze at low temperatures. Remaining always in liquid form, it flows through the engine, absorbing its heat and redistributing it, and the circuit of hoses and channels traveled by this liquid is collectively called the "water jacket."
To accomplish this redistribution of heat, an accessory water pump, driven by the engine’s power, pumps the coolant forward from the engine and through a radiator. A fan, also engine-driven, draws air over the fine cooling fins of the radiator, through which hot coolant is being pumped, and transfers the engine’s heat into the surrounding air. The cooler liquid now returns through another hose to the water pump for recirculation. Additionally, a thermostat regulates the routing of coolant flow depending on how hot the engine is, and the heater core of the car’s HVAC system also draws its heat from this water jacket.
So why does a vehicle overheat? The root causes can be numerous, although they tend to express themselves in a core group of symptoms. A leak, which can be caused by cracked old hoses, a faulty radiator or water pump, or a dry gasket somewhere in the cooling system, will allow coolant to gradually leak from the car. Remember, the water jacket must be a closed, recirculating system to properly function; adding water to a leaking radiator or replenishing the coolant overflow reservoir under the hood are only temporary solutions.
Cars are more likely to overheat in hot weather, though usually only in conjunction with other exacerbating factors such as low airflow over the radiator from sitting at length in slow traffic. Overheating may also be caused by a blockage somewhere in the water jacket, which can form as the coolant ages.
What To Do:
If your car is overheating on you, it may be happening for a variety of reasons, but there is only one thing you should initially do, and it’s crucially important that you do it as soon as possible:
- Pull over, get off the freeway, get into a parking lot.
- Turn off the car as soon as possible and allow the vehicle to cool for at least 10 minutes.
- A half-hour would be better. Sure, you can turn on the heat and open the windows – this will engage the heater core as a secondary radiator, helping to dissipate the heat – but that is an emergency measure only. You must cease the engine’s production of heat as soon as possible by turning it off.
- Until the vehicle is much cooler, absolutely do not unscrew the radiator cap (or, on some models, the coolant reservoir cap). The cooling system is hot and pressurized – it could boil violently, overflow, and scald you if suddenly depressurized while hot.
- Once the car is cool, attempt to identify the leak and repair it if possible. Your goal now is to get the vehicle to a location where a proper repair can be done. If it can be driven there without further overheat, this is desirable, but it may be necessary to call a tow truck.
Bottom line:
The best way to prevent an overheat is to periodically monitor your vehicle’s cooling system. Be vigilant for any leaks, and replace hoses preventatively as they age. The coolant should be flushed and replaced every few years or 30,000 miles. At longer intervals, the radiator or water pump may begin to fail. These types of problems are generally noticeable and minor, if attended to on a preventative basis. However, if ignored, an overheat condition will quickly destroy your engine. This is a certainty; cooling system problems should always be addressed quickly!
