It is perhaps one of the most common of breakdowns that can sometimes happen with little warning. When your car overheats, it means your car’s cooling systems is being overwhelmed by the engine and ambient heat and is not working in its optimum state. What to do?
In most extreme cases, engine overheating can cause permanent damage of engine internal components, engine seizure, or even cause the engine to go up in flames – hence your car’s cooling system is not something to be taken lightly.
Also, overheating can affect both new and old cars – in older cars, overheating can be caused by failing of components such as the water pump and thermostat, in newer cars (with more electronics), overheating can be the cause of failed electrical systems such as sensors and cooling fans.
Therefore, before we understand what happens when your car overheats, let's begin with understanding the major components of your car’s cooling system and their typical faults, that cause overheating.
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The radiator is the biggest component of your cars cooling system, the radiator functions as a heat exchanger to remove heat from engine coolant as it is pumped through it. Coolant passes through small channels within the radiator (typically) from the left to right or vice versa, as the coolant passes across the radiator, it is cooled by air that passes through from the front to the back of the radiator. The air is either blown by the cooling fan(s) or air that naturally passes through the front of your car as you drive.
Typical faults: Radiators can rupture or leak after many years of service, typically plastic components used in its construction can get brittle and crack/fail causing leaks (both small and huge). A leaking radiator will cause coolant to be drained, severely affecting the cooling system. Once the systems loses too much coolant, the car will begin to overheat.
In certain cases, radiators can suffer from a build-up of rust or contaminants within its cooling channels. This build-up can cause blockages within the radiator, making it inefficient, thus causing the engine to overheat.
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The water pump is perhaps the second most important component in your cooling system – like the name suggests, the water pump is driven by the engine, and (or via a motor) in newer cars, and pumps water throughout the engine and cooling system.
Typical faults: The water pump is another point in the car’s cooling system that can sprout leaks. Here again, excessive loss of coolant can cause the engine to overheat. In extreme cases – typically in older cars – the water pump can jam causing sudden failure. With that said, this can also happen in newer cars with electric pumps that fail over time.
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Most cars will have one, two or multiple fans to aid the cooling system. In most cases, because water alone is not enough to cool a car down, fans are used to blow cool air across the radiator and engine and remove heat.
Typical faults: This is perhaps the most common type of fault besides a leaky radiator that causes a car to overheat. One or multiple fans may stop working over time, this causes engine temperatures to rise, especially when sitting in traffic or when crawling at low speeds. When the cooling fans stop working, other parts of the cooling system are overwhelmed, and this can cause engine temperatures to go up.
Your car’s cooling system is made up of an intricate circuit of cooling hoses to cool all the necessary components of the engine. For this, rubber or polymer hoses snake to and from the engine, and into the radiators to provide cooling.
Typical faults: Ruptured or cracks in the hoses can cause coolant to leak and evacuate the system. Too little coolant and, you guessed it… the engine overheats.
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The thermostat is perhaps the most overlooked item in your cooling system – and in many cases can cause major problems if it doesn’t work properly. The thermostat regulates the coolant flow within the cooling system. Think of it as a valve that opens and closes to regulate and ensure the engine is at its optimum operating temperature.
When it’s closed (engine cool) – the thermostat blocks off water that is circulating in the engine from going through the radiator – this allows the engine to warm up to its operating temperature. Once the engine temperature hits a set limit, the thermostat opens and allows coolant to flow through the engine and through the radiator to cool it down again.
Typical faults: Thermostats typically jam after years of service. Once jammed, water will not circulate between the engine and radiator as it should. If jammed in a fully-closed position, your car can overheat within minutes of driving.
Cooling system sensors
Newer cars usually employ one or more temperature sensors that feed information to the car’s computer to regulate the cooling system. Unlike older cars, where the cooling systems consist mainly of mechanical components (such as the water pump, and thermostat), newer cars employ electronic water pumps, thermostats and cooling fans. Their functions are controlled by the car’s computer to regulate cooling.
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Typical faults: Temperature sensors, like most electronic components, can fail over time. When they do fail, they provide incorrect/null readings to the car’s computer which then affect the operation of other items, such as the thermostat. Faults like this will normally throw up an engine fault code which should be looked at the soonest.
Cooling systems typically require a reservoir tank to store excess coolant and to regulate the flow of water within the cooling system depending on the engine’s requirements.
Typical faults: Reservoir tanks are typically made from plastic which become brittle over time. Like any other plastic component, they can crack and/or rupture causing coolant to drain out.
My car has overheated what do I do now?
First things first, don’t panic. Follow these simple steps:
- As soon as you see you car’s temperature needle rising higher than usual or if it has hit the maximum range of your engine temperature gauge, chances are it's overheating. Urgently find a safe place to stop the car, and turn off the engine.
- Turn on your Emergency Signals and unlock your bonnet.
- Before opening your bonnet, observe for traces of steam. If there is no steam or hot vapour coming from the engine bay area, carefully unlatch and open the bonnet.
- At this point, it’s best to let the car cool down. This will normally take around 30-45 mins. Leave the bonnet open.
- If there are visible coolant leaks, it could be coming out of the radiator or the reservoir tank – take note of this, snap a photo if possible, but DO NOT put your face/hands close to the engine or its components. The cooling system is under immense pressure when overheated, do not attempt to touch anything until the car has properly cooled down.
- When you feel the car has properly cooled down, get your key and put the car into ignition mode – if with a key, turn to the second position/notch (for cars with Keyless Start, press the Start/Stop button without depressing the brake pedal) – this will normally bring your car’s instrument cluster to life. Now you’ll be able to check if your car temperature is back to normal or still needs further cooling. The lower, the better.
Now try and diagnose the problem, and see if you can continue your journey…
- The first thing to do is check if there’s coolant in the system – you can do this by checking the reservoir tank level or the level within the radiator.
- If the water level is low, try topping-up the system with water. If in a pinch, tap water is fine even if you can’t get coolant.
- Once the system is topped-off, restart your car and check if your engine temperature is holding. If at this point, the temperature is holding, and there are no major leaks, then the chances are you might have a small leak in your system but you can try to drive the car slowly back to your home or mechanic. Keep a constant eye on your temperature gauge.
- If there is water/coolant in the system, but the engine temperature is still rising gradually, the chances are one of the cooling fans are not working properly, try switching on the air-conditioning (AC), and see if the Auxiliary (Aux) Fan starts to spin. If the Aux fan does not come on, turn off the AC and see if the temperature gauge holds steady. If it does, you could probably try to nurse the car home without turning on the AC, but try your best to avoid traffic.
- If your coolant system has fluid and the cooling fans are coming on as they should, chances are this might be an issue with your thermostat and/or water pump. In cases like these, it is best to not continue your journey and call a tow truck. You're better off not taking the risk and causing any further damage to your engine.
- Do note that symptoms and causes may vary from car to car; this is a limited and simplified guide.
- Therefore, if your car is overheating, it’s best to have your car looked at by a competent mechanic before further use, do not postpone any repairs, and do keep using the car simply because you feel it might be a one-off event.
How do I look after my cooling system…
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Preventive maintenance is the best way to ensure your car keeps going smoothly and safely. These are simple steps to ensuring your car’s cooling system is working great at all times:
- The number one thing you can do is always ensure your coolant levels are at their optimum level. Check this at least once every two weeks.
- Change the coolant at the manufacturer specified intervals. This interval can range between every 30,000km to even 60,000km so check your owner’s manual or with the service centre.
- Use manufacturer specified coolant or coolant additives only.
- Refrain from using mineral water in your cooling system as it contains minerals such as Calcium and Magnesium which can oxidise and cause corrosion over time.
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- Performing a radiator flush (at specified intervals) has its benefits but do check with your mechanic/service centre if required.
- Replace your thermostat as specified by the manufacturer. It’s a service item and should be replaced on time.
- Perform a visual or diagnostics test (for newer cars) of your cooling fans from time to time. Typically, these items degrade over time, so frequent inspections help in ensuring everything is working fine.
- Change the water pump if required or if visible signs of failure begin to show. Check this with your mechanic.