Why does your car engine overheat?
A car’s engine comprises many components. Each component complements others to perform the required function. If any complication happens to one part, it impacts the whole system.
For example, your car’s engine contains a cooling system. The cooling system is supposed to manage excessive heat generation. But if it stops functioning properly, it can lead to engine overheating. Similarly, there may be other reasons why your vehicle’s engine overheats.
Common Reasons for a Car’s Engine Overheating
Below are the major reasons for engine overheating.
1. Lack of coolant
A coolant is an antifreeze called ethylene glycol diluted with water. This solution freezes at a lower temperature than water. Thus, it serves as a better coolant than water in cold weather conditions. The role of a coolant is to maintain a suitable temperature in the engine and save it from overheating. If the coolant doesn’t reach the radiator due to pump malfunction, blockage or leak, it can cause engine heating.
2. Faulty thermostat
The thermostat of a vehicle’s engine manages the flow of coolant. It only allows the coolant to flow when the engine heats. The main valve of a thermostat stays shut if the engine is cool or idling. For some reason, if the thermostat can’t regulate the coolant flow, it can result in engine heating. This happens when the thermostat fails to open the valves, preventing the engine radiator from receiving the coolant.
3. Damaged radiator fan
The coolant flows through the radiator after absorbing heat from the engine. The radiator’s cooling fan brings down its temperature by allowing the coolant to transfer the heat to the atmosphere. If the cooling fan is not functioning at an optimum level, it reduces the cooling efficiency of the coolant. This problem may occur due to a mechanical failure in the electric motor that runs the radiator fan.
4. Low engine oil
Engine oil in your car provides lubrication and helps to reduce excess engine heat as well. If your car runs low on engine oil, it can also cause excessive engine heating.
5. Damaged expansion tank
Almost all vehicles contain a coolant expansion tank these days. It regulates the entire cooling system’s pressure. However, if the expansion tank is unable to release the pressure from the radiator, it can cause overheating in the engine.
6. Restricted airflow
The radiator needs sufficient airflow when the car is moving to disperse heat from the coolant. Front grilles blocked by debris or leaves, bent fins, or a jammed clutch fan can restrict airflow through the radiator, resulting in engine overheating.
7. Excessive engine load
Dragging heavy loads, driving continuously in stop-and-go traffic, hauling overloaded cargo, or climbing steep grades generates excessive heat in the engine. This additional load can overwhelm the cooling system and cause overheating if the engine RPM is not increased.
8. Leaking or blown head gasket
The head gasket seals the combustion chamber and prevents engine coolant from leaking. A blown or leaking head gasket allows coolant to enter the cylinders. This reduces cooling efficiency and causes the engine to overheat.
9. Faulty water pump
The water pump circulates engine coolant through the cooling system. If the pump is worn out or damaged, it will fail to maintain adequate coolant flow. Insufficient coolant circulation due to a faulty water pump is a common cause of engine overheating.
10. Clogged radiator or condenser fins
The radiator and condenser use many small fins to dissipate heat. Over time, debris blocks airflow through these fins. This reduces the heat transfer efficiency of the cooling system. Clogged fins lead to impaired cooling capacity, causing the engine to overheat.
How to diagnose an overheating engine?
If you can diagnose the warning signs early on, it can save your car from serious damage. You already know what happens internally when a car overheats. Now, let’s talk about the signs you should notice from the outside to diagnose if a car’s engine is overheating.
Signs of car overheating
Here are some of the signs you can notice to fix the engine heating issue as soon as possible.
1. Hot bonnet
It is common for your car's bonnet to feel warm. But if it gets extremely hot, it means that your engine is emitting excessive heat.
2. Temperature indicator
Most cars come with an indicator that reflects the engine’s temperature. This indicator will help you realise whenever your car’s engine generates excessive heat. However, such an indicator reads the coolant’s temperature. So, you can’t trust it if car overheating occurs due to coolant leakage.
3. Strange noise
If you hear a ticking noise from the engine, it means a lack of lubrication. This happens when the engine oil loses its ability to lubricate due to excessive heating.
4. Coolant leakage
If you find coolant leaking beneath your car, it may be causing your engine to overheat due to a lack of cooling liquid.
5. Burning smell
If the engine overheats, you might smell an odour of burning oil. The smell intensifies as the heat rises to damage plastic valves, rubber seals, etc.
6. Steam coming out of the bonnet
If you are able to see steam coming out of the bonnet, it can be a sign of engine heating. This happens when the coolant starts turning into steam after reaching its boiling point.
7. Reduced performance
When overheated, your car’s engine won’t be able to deliver its regular performance. Combine this with other signs, and you will know when to fix the excessive heating issue in your engine.
8. Low coolant warning light
A specific "Low Coolant" or "Check Engine Coolant" warning light may illuminate your dashboard if the coolant level is critically low. This could be due to external leakage or internal coolant consumption, signalling a blown head gasket or cracked engine block.
10. Sweet-smelling exhaust
White or blueish sweet-smelling exhaust indicates coolant is leaking into the combustion chamber and being burned along with fuel. This is a clear sign of internal engine damage, like a blown head gasket. Do not attempt to drive with this symptom, as it can lead to total engine failure.
Engine overheating troubleshooting
You should know what to do when a car overheats to avoid extreme damage. Here are the steps you can follow in case engine heating occurs.
Step 1: Switch Off the Car's Air-Conditioning to Decrease Engine Pressure.
Step 2: Park your car in a safe location, shut it off and let the engine cool down for 15-20 minutes.
Step 3: Check the coolant level and add more if required.
Step 4: Restart the engine or get it towed if you’re not able to start it.
Step 5: Take the car to a professional to check for leakage, blockage or any other damage.
Ways to keep your car engine in good condition
Use the following habits to prevent engine overheating in your car.
1. Regularly check the coolant level
This is a useful habit to avoid excessive heating in the engine of your car. Checking the coolant level in the radiator will help you add fluid whenever required. It is the most basic approach to prevent engine overheating. But make sure that the engine is cool before opening the radiator to check the coolant level.
2. Manage the AC usage to reduce engine pressure
Whenever you drive your car on a long journey, manage the use of air-conditioner (AC). Turn off the AC from time to time to avoid extra load on the engine. Continuously running AC increases the chances of engine overheating on long journeys.
You can also turn on the heater after switching off the AC and open the windows. This approach will allow the heat from the engine to release into the atmosphere through the cabin. This process is definitely a bit uncomfortable in summers but allows you to keep on moving without facing the issue of an overheated engine.
3. Keep an eye on the temperature indicator
When you are enjoying a long road trip, don’t forget to check the engine’s health through the temperature indicator. It may be a gauge or light on your dashboard, depending on the car you drive.
By checking the engine temperature, you can manage the speed or stop from time to time to avoid overheating.
4. Maintain a cycle of radiator flushing
Keeping an optimum level of coolant in your vehicle isn’t enough; you must replace it periodically. This can be done via a process called radiator flushing, which involves draining the coolant out of the radiator.
You can ask a professional at your regular service centre to flush the radiator. Make sure the mechanic cleans the radiator lines properly before filling up the new coolant. Doing this periodically will ensure optimum performance from the engine’s coolant.
5. Get the thermostat checked regularly
Another component you should get checked regularly is the thermostat. This way, you can fix any minor problems with the thermostat early on to maintain a smooth flow of coolant.
6. Notice any damages on the radiator cap
The cap on the radiator also plays its part. A loosened or faulty cap causes a pressure difference, which impacts the circulation of liquid. This cap contains a spring that loses its strength over time. Thus, you need to get it replaced whenever required to avoid overheating due to pressure differences.
7. Replace an old car battery
An old car battery has to work harder to deliver the required power. Weak batteries need to consistently recharge to deliver energy, which leads to excessive engine heating. It can cause overheating inside the engine. You should get your car’s battery checked by a mechanic. He will tell you if it is the right time to replace the old battery with a new one.
8. Regular oil changes
Get regular oil and filter changes as per the manufacturer's recommendation. Old contaminated oil can't properly lubricate and cool the engine, leading to overheating.
9. Drive gently
Avoid sudden acceleration and hard braking. Aggressive driving causes premature wear and tear and makes the engine prone to overheating. Gentle acceleration and braking reduce strain on the engine.
10. Clean the radiator
Use a garden hose with a spray nozzle to gently clean dust, bugs and debris clogging the radiator fins and AC condenser at least once a year or when you notice reduced AC performance. This ensures optimal airflow.
Tips to prevent your car from overheating
An overheated cabin can also impact the efficiency of the engine as the AC inside the car puts more pressure to cool down the interior. Hence, you must try to maintain a normal temperature of the car at all times. Below are some tips to help you avoid car heating.
1. Park in the shade
If you leave your car parked out in the sun, it can increase the temperature not just in the cabin but also inside the bonnet. Moreover, a heated cabin requires more time to cool down after turning on the AC.
You should find a parking space with shade, especially if you want to park the vehicle for a long period. Alternatively, you can cover your car to reduce heat absorption.
2. Leave windows slightly open for natural ventilation
If you keep all car windows closed while parking, it traps the hot air inside. Leaving the windows slightly open allows the hot air to escape.
If you have a sunroof in your car, open it just a little bit while parking. This creates natural ventilation, keeping the cabin cool.
However, you must keep the weather conditions in mind while leaving the windows open. You wouldn’t want to come back to a soggy cabin after sudden summer rainfall.
3. Use the car’s AC smartly
You must use the air-conditioner in a way that it doesn’t put too much pressure on the engine. For instance, don’t start the AC in recirculation mode. Instead, leave it in the fresh air mode for the first 10 minutes.
The recirculation setting will just move the same hot air inside. Once the cabin air cools down, you can switch the AC to the recirculation mode.
4. Use sun reflectors
Sun reflectors are made of metallic coated fabrics or folding cardboard that can be placed over the windshield and side windows when your car is parked in the sun. The reflective surface bounces back much of the sun's infrared and UV rays rather than letting them penetrate the glass. This reduces the greenhouse effect inside the car cabin by lowering heat buildup by around 40-60°F compared to not using reflectors.
5. Get window tinting
Dark-tinted films containing microscopic metal particles applied on the vehicle's window glass prevent a significant amount of solar radiation from entering the cabin. Light colours let in more heat while darker shades like charcoal black absorb and block up to 95% of UV and infrared rays, keeping interiors cooler by around 30-50°F. However, visibility and legality regulations limit allowable tint darkness levels for driver and passenger windows.
6. Service the AC
It is important to get comprehensive AC diagnostics and servicing done before summer. This involves checking for refrigerant leaks, compressor operation, flushing contaminated oil and replacing the drying filter. Any leaks need to be sealed to prevent refrigerant loss, which reduces AC cooling capacity. Lack of cabin cooling makes the engine work harder, leading to overheating.
7. Drive at moderate speeds
At highway speeds above 80 kph, aerodynamic drag increases exponentially due to wind resistance requiring more engine effort and fuel to overcome it. This additional load can overwhelm the engine cooling system, especially in hot conditions. Keeping speeds moderate, around 70-80 kph, allows just enough airflow through the radiator to cool the coolant without straining the engine.
8. Flush the radiator
Over time, rust, minerals and sludge can build up inside the radiator, blocking coolant flow. Use a radiator flush kit to dissolve these deposits. Drain, thoroughly rinse with water, and refill with fresh coolant/distilled water mix. This improves heat transfer and cooling efficiency.
9. Check cooling fans
Electric cooling fans mounted behind the radiator should turn on when the engine reaches operating temperature. Check fan operation visually or use an OBDII scanner. Replace defective fans immediately, as they are vital for air circulation when the car is idling or in slow traffic.
10. Watch your route
Carefully watch the route and any inclines when driving in hot weather. Steep uphill climbs, particularly with a fully loaded vehicle, strain the engine and cooling system significantly. Try to avoid continuous uphill driving and stop to let the engine cool if the temperature gauge starts creeping up.
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