Why Does My Car Overheat When Idling?

In a car’s engine, there is a lot of combustion and friction that generates a lot of heat. As a result, there is a need for continuous cooling whenever the engine is operating.

When the engine cooling system fails or is subjected to hard conditions, there are high chances of overheating.

However, when the engine is idle, there is minimal combustion, and it should not overheat. If it does, there is a problem. But why does my car overheat when idling?

A car is equipped with a cooling system that is meant to keep the vehicle cool even when it’s idle. If one of the components fails, then the whole system fails, resulting in overheating.

How Do You Know Your Car Is Overheating?

The ability to determine the signs of an overheating engine can save you from severe engine damage. When an engine overheats, the pistons expand and can’t fit in the cylinder bore.

Continuous usage of a vehicle’s engine while overheating might crack the cylinder heads and engine block.

Below are some signs to help you easily identify when your vehicle is overheating.

1. Coolant leaking on the ground

In case you notice coolant spillage under your car, it may be a leak in your cooling system.

It can also signify that your engine has overheated and boiled the coolant in the radiator, triggering the overflow tank to get rid of excess coolant due to the high pressure in the radiator.

When the coolant is leaking, it implies that the cooling system will not have the recommended amount of coolant hence a major contributor to overheating.

2. Smells hot

When the engine is overheating, there is a unique odor emitted from burning oil.

As the temperature goes high, plastic valves, bits of resin, and rubber seals in the engine start to melt hence producing fumes.

Leaking coolant also fills the car with a sweet smell since it contains ethylene glycol. Any strange odors are a warning and should not be ignored.

3. Steam coming from the hood

Steam originating below your hood is a sure sign of engine overheating. Once this happens, stop the car and switch off the engine.

When the coolant is heated and reaches boiling point, it is converted to steam creating high pressure in the cooling system. The steam escapes through a coolant reservoir or radiator cap.

4. Thumping Noises

A thermostat in the cooling system regulates the valve that allows coolant to flow into the radiator. When the valve is stuck, coolant already in the engines gets super-heated.

When the super-heated coolant comes into contact with cold coolant, a loud thumping noise is produced. This is fixed through the replacement of the thermostat.

5. Reduced Engine power

Once your engine overheats, it cannot produce enough power to propel your car at the normal rate.

If you feel the engine is struggling to propel the vehicle, pay attention to noises or smells related to engine overheating. Keep checking the temperature gauge and stop the vehicle if it’s overheating.

6. Hot Hood

When the vehicle is running, the hood is normally warm to the touch. But if the hood is very hot, then you should be concerned. In normal conditions, you can comfortably place your hand on the hood for 15 seconds.

7. Ticking Sound

If there is a ticking sound originating from your engine, that means the engine oil is not sufficiently lubricating the moving parts.

When the engine oil is extremely hot, it can’t lubricate properly, and it functions more like hot water than oil. If the engine parts are grinding on each other, they will experience significant wear and tear faster than usual.

Why Does My Car Overheat When Idling?

Below are some of the commons reasons why car overheats when idle:

1. Clogged radiator

The radiator is where coolant comes to cool down and when it malfunctions, coolant flow is disrupted. The radiator doesn’t just fail on its own. Mostly, the coolant is the cause of the failure. The use of low-quality antifreeze leads to high corrosion.

Using water as a coolant leads to corrosion, while antifreeze keeps components from rusting. When rust builds up in the radiator, then coolant flow is disrupted hence overheating problems. Flush your radiator every half year or yearly to prevent clogging.

2. Broken radiator fan

When there is not enough airflow to cool the coolant, the radiator fans kick in and send more air to cool the coolant, which in turn cools the engine. When the fans become faulty or blades are broken, there isn’t enough airflow to cool the coolant.

In some older versions of cars, the problem may be caused by a faulty belt because the fans are driven by a belt. But in modern cars, fans are driven by a battery. If you notice your vehicle heating up when idle, a broken radiator fan may be the cause.

3. Low coolant level

When your car begins to overheat when idle, low or no coolant is a major cause since it is used to cool down the engine.

Do not use low-quality coolant products or regular water since they won’t absorb heat effectively, leaving the engine hotter. There is a possibility of coolant leaks if the levels keep changing drastically.

If the coolant is present but it’s dirty, then it doesn’t serve its purpose. Coolant needs to be changed regularly. Otherwise, it won’t be as efficient as it should be and might cause overheating.

4. Thermostat problem

The Thermostat plays the role of deciding when to release coolant into the engine. When the temperature goes high, the Thermostat allows the valve to open; hence coolant flows in to cool the engine.

When the thermostat malfunctions, the coolant doesn’t flow into the engine when needed. This results in overheating when the vehicle is idle.

5. Bad water pump

Your coolant may be at the right levels, but the vehicle still overheats. No matter how much coolant you have, if there is no means to move it in the engine, then it’s of no help.

The water pump builds pressure to pump the coolant through the engine. Its failure means no circulation of the coolant in the engine hence overheating.

6. Air in the system

The cooling system is pressurized. When the air enters the system, there is inadequate pressure to push the coolant through the engine.

Air in the system is a result of a leak. The way the coolant leaks out is the same way the air gets into the system. When you forget to properly put the cap on after refilling the coolant, then air finds its way into the system.

What Do I Do If My Car Is Overheating?

If your car is overheating, you need to:

1. Kill the air conditioner and crank the heat

Begin by turning off the air conditioner to relieve stress on the engine. Then turn the controller to maximum heat and roll down the windows for the heat to get out since it might be uncomfortably hot.

2.  Find a safe place and stop the car

Pull over and switch off the car. Wait at least 15 minutes for the engine to cool down to reduce pressure in the cooling system to a safe level.

While waiting, check the gauge to know when the heat levels have gone down. Do not open the hood while temperatures are high, as the overheated fluids in the engine in the form of vapor might burn your skin.

3. Investigate the cause of the heating

Investigate the possible reasons for your car overheating. If your car’s coolant level is low, add up to the recommended level. After stopping, restart the vehicle and drive carefully to the nearest repair shop.

Topping up coolant won’t help if your car is heating due to other reasons, such as a broken water pump or radiator fan.

The other major reasons, such as broken radiators, thermostats, and others discussed above, will require professional help. If you are not near a mechanic, you will need to tow the vehicle.

Do not drive your car if it’s overheating since you might damage the engine leading to costly repairs.

Tips To Keep Your Car From Overheating

1. Check your cars coolant level regularly

Always make it a habit to check coolant levels regularly. Check the levels inside the radiator or the coolant reservoir. Make sure they are in the recommended levels.

This practice is very crucial to prevent your car from overheating. Always remember that a low coolant level is one of the major reasons for vehicle overheating. When opening the radiator cap to check the coolant, ensure the engine is cool.

2. Keep checking the temperature gauge

When on a road trip, you tend to forget about your precious car since you are having fun. When driving, always be keen and constantly check the temperature gauge.

If you are on a long trip, make stopovers and do not let the gauge go beyond normal temperature; otherwise, you will kill your engine.

3. Turn off the AC to reduce engine load

If you are traveling for a long distance and notice that your car is about to overheat, but you can’t stop, the short-term solution is to turn off the air conditioner.

Turning off the AC helps reduce stress on the engine. This will help you drive for a longer distance before the vehicle starts to overheat. Additionally, turn on the heater and open the windows for the heat in the cabin to get out.

4. Pull over when the engine starts to overheat

In case your vehicle begins to overheat, the safest solution is to halt immediately. Look for a safe location and park the car and open the hood for the heat to escape faster. After cooling for 15 to 20 minutes, pour cold water over the radiator for further cooling.

Do not add water to the radiator immediately. You might end up cracking the engine block, which will cost a lot to repair. So refrain from adding cold water when the engine is overheated.

5. Periodic radiator flushing

Keeping the coolant of your car at the recommended level is a good practice. Although, you have to periodically replace the coolant.

The flushing process involves completely draining the old coolant, cleaning the radiator using a flush fluid, and then adding a new coolant to the system.

6. Keeping a check on the Thermostat

The Thermostat plays an important role in regulating the coolant flow. Therefore, when servicing your vehicle, ask your mechanic to check the Thermostat.

If the thermostat is not working, then the probability of the car overheating is very high.

7. Check radiator cap for damage

The radiator cap has a lot of work to do. If it’s faulty or not fastened well, it causes a difference in the pressure at which the coolant is circulated. The cap has a spring that weakens with time and should be replaced immediately.

Can A Bad Alternator Cause A Car To Overheat?

Yes. If the alternator dies, it causes the battery to die as well. In addition, the fans relay requires a specific amount of voltage to be active.

Therefore, with both the alternator and battery dead, insufficient voltage is produced to activate the radiator fans, leading to overheating. So you need to test your alternator.

 How long can a car idle before overheating?

First, it depends on the climate of the environment. For people in cold places such as Canada and Alaska, it is possible to leave a car engine idling for days, and it will not overheat.

This is mostly done by people who do not have heated garages during winter. However, prolonged idling can ruin your engine if you live in a hot environment.


An overheating engine is a sign of trouble. To ensure the engine is at a recommended temperature, a cooling system was developed. If the cooling system is working properly, then the engine won’t overheat.

Always make sure that you pay attention to any alarming signs of engine overheating, and if your car has that problem addressed, it quickly to avoid complete engine damage. Maintaining the vehicle cooling system regularly saves you money and time for major repairs.

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