Why Does My Car Overheat While Idling?

Why Does My Car Overheat While Idling? With all the activities that take place in the engine of your vehicle, it is not abnormal for the engine to develop some faults and start overheating. Intermittent overheating of the engine is dangerous and can reduce your engine’s life expectancy.

Your car overheating while idling can be caused by a wide range of factors that will be discussed as we progress in this article. On your part, you must be able to identify most warning signs of an overheating engine. Identifying these signs will enable you to solve the problem before it becomes severe.

An engine overheating while idling occurs when the engine is not receiving enough fluids. The coolant may have dried up in the reservoir or there may be a faulty component in the engine compartment.

It is unsafe to overlook engine overheating. Hence, you must inspect the various components of the engine and other parts of your car to decipher where the problem is coming from and fix it immediately.

In this article, we will explore everything you need to know about a car overheating, especially why your car overheats while idling.

What is Engine Overheating?

Before delving into the causes of engine overheating, it is important to understand the concept of engine overheating.

Engine overheating is simply a situation where the engine’s temperature rises above its normal operating temperature level. The normal temperature range of an engine is between 195° to 220° degrees, and when your engine has a temperature above this range, it can be tagged “an overheating engine.”

At this point, your engine is running too hot and should be a cause of concern. Modern vehicles are designed with sophisticated cooling systems that are equipped with heat sensors and electric fans, to keep your engine working efficiently in any weather.

However, with these technologies employed, your engine might still overheat, and this is due to a variety of reasons which will be revealed as we go further.

Can you drive a Car with an Overheating Engine?

No! It is very dangerous to drive with an overheating engine. Apart from the grave and sometimes permanent damages it can cause to the engine, it is also life-threatening. An overheating engine can cause your car to stall in the middle of a highway which could lead to an accident.

The engine’s temperature is controlled by the cooling system and if there is a problem with any component of the system (e.g., radiator cap), overheating will occur and can result in engine stalling because the sensor is giving wrong readings to the control module.

Also, if there is still coolant in your engine, but there is a problem with the thermostat, the coolant will boil beyond its normal temperature because the damaged thermostat valve is restricting the flow of coolant. This will cause pressure to build up and this pressure can blow up components like the head gasket, tubes, and hoses.

When your engine overheats, it indicates a serious problem. Rather than continuing to drive an overheated engine, it is important to pull over and check what has gone wrong in the engine or tow your car to the nearest auto repair shop.

The Primary Cause of Overheating and Why it is Bad for your Engine

The primary cause of engine overheating is a problem with any component of your car’s cooling system. The cooling system of your car is made up of components such as the radiator, radiator pressure cap, pump, thermostat, electric fan, hoses, and overflow reservoir.

All these components play different roles in keeping your vehicle at the right operating temperature and if there is a problem with any of them, it can lead to engine overheating.

When the engine temperature goes above its normal operating temperature, you are advised to park your car and let it cool down for a while. However, some people continue driving their cars in this condition.

This act will cause the coolant in the reservoir to keep boiling up and expand, which will blow up and destroy vital components in the engine such as the head gaskets, hoses, connecting rods, and rings due to the force from the expanded coolant.

Reasons your Engine Overheats while Idling

Your engine can overheat while idling due to some issues related to the cooling system. A problem with the cooling system will prevent the adequate quantity of coolant from getting to the engine. It can also make the coolant dry up easily or lead to coolant leakage and inadequate pressure in the cooling system.

Here are some of the reasons your engine will overheat.

Bad water pump

A bad water pump is one reason your engine will overheat.

No matter the quantity of coolant you have in the reservoir, if the water pump is not working, the engine will still overheat because it is not receiving coolant when needed.

The water pump is an essential component of the cooling system that creates the pressure which moves coolant from the reservoir to the engine and other components.

Water pumps are designed to last for up to 60,000 miles and will last this long if properly maintained. They go bad after this period and could be the reason your engine is overheating. Replacing a bad water pump will cost between $400 to $600, inclusive of labor.

Low or no coolant in the reservoir

A complete absence or low coolant in the reservoir will cause your engine to overheat. Coolant can leak out from a broken hose or a faulty reservoir cap which will drastically reduce the amount of coolant required to keep the engine running.

If the coolant reservoir is not refilled after this happens, there will be a low coolant level or no coolant at all in the reservoir.  Hence, it is very important to inspect your engine frequently to know when to refill the coolant tank, fix broken hoses, or replace faulty radiator caps.

Other times, a low coolant level can be due to the climate and weather conditions in the area you reside. Extremely cold temperatures will cause the coolant particles to contract and become solid. Using high-quality coolants that have less percentage of water in them will help reduce the occurrence of this.

Clogged radiator

The radiator is a component in the engine compartment where hot coolant goes to cool down. The radiator contains coolant which helps to cool down the hot coolant coming from the engine and sends it back to the engine.

Coolant flows through the engine and the radiator, this process ensures that the engine remains at its normal operating temperature. If the radiator is clogged with rust or other contaminants, the free flow of coolant will be interrupted, and this will cause your engine to overheat.

Servicing a clogged radiator will not cost more than $100.

Bad thermostat

A thermostat is a small device installed in the engine that controls when coolant should be sent to the engine and when it should be stopped, by closing or opening its valve for coolant to pass to the engine.

A bad thermostat will either be stuck open or stuck closed.

A thermostat in an open position will allow coolant to flow freely into the engine and radiator which is not good for the engine because it will not allow the engine to heat up to its normal operating temperature.

On the other hand, if the thermostat valve is stuck close, it will restrict the flow of coolant to the engine, which will cause the overheating of your engine even while idling.

A faulty thermostat cannot be repaired. The component can only be replaced and fortunately, replacing a bad thermostat is cheap. It will cost between $100 to $250 depending on your car model and make.

Broken radiator fan

A broken radiator fan is one of the top causes of an engine overheating while idling. Radiator fans are of two different types: the electric radiator fan and the belt-driven fan.

When your car is idling, the air is no longer flowing into the engine to blow off the heat radiating from the hot coolant. At this point, the radiator fan helps to reduce the heat through forced convection, a forced heat transfer method.

Thus, a broken or malfunctioning radiator fan will not perform this task and will cause the engine to overheat. If your engine is overheating and it’s caused by the radiator fan, you should have the fan fixed or replaced.

Air in the system

Air finding its way into the cooling system will cause your engine to overheat. This is because, when there is excess air in the system, the coolant will lack the pressure needed to flow to the engine which will lead to overheating.

Air in the cooling system is usually a result of a leak from any of the components that make up the cooling system or failure to close and properly place components in the cooling system after opening them.

What to do when the Engine Overheats when Idle

If your engine overheats while idling, there’s a probability that this might continue when you start driving.

When this happens, you should inspect the engine and try to diagnose the problem on your own, as some issues are quite easy to diagnose.

Here are some tips to guide you when your engine overheats when idle.

  • When you are in this situation, do not panic, do not continue driving and when you pull over to inspect, do not open the hood immediately.
  • Turn off the air conditioner: If you notice your engine is overheating while you are idling, turn off the air conditioner to reduce the stress on the engine. Since you were not driving with the overheated engine, the damage might be minimal. After turning off the air conditioner, turn the dial to maximum heat to help draw heat from the engine and allow you to move the car to a better spot.
  • Pull over in a safe spot: When you locate a safe spot to park your car, pull over and shut down the car completely. This will give the engine time to cool down. You can monitor its progress on the temperature gauge as it will return to its normal range as the engine cools.
  • Check your coolant level: This is important to know if you still have coolant in the reservoir or if the coolant level is low. If the problem is due to a lack of coolant in the reservoir, topping it would help cool down the engine.
  • Inspect other components in the engine and most importantly the radiator fan: If the problem is not related to coolant level, it could be with other components like the radiator fan, thermostat valve or water pump. An issue with any of these components could be the reason your engine is overheating when idle.
  • Call for help: If you are unable to detect the problem, you should seek professional help. You can call a mechanic or tow the vehicle to the nearest auto repair shop.
  • The cost of repair will vary depending on the component that is damaged.

Frequently Asked Questions

Can you pour water over the engine to cool it down?

No! if your engine is hot, do not pour water on it rather allow it to air-cool. If there is a need to add water to the engine, it should be filled in the radiator when it has cooled down. You cannot open a hot radiator cap, which is why you must let it cool before opening it to add water. Pouring cold water on a hot engine will suddenly change the inner and outer temperature of the engine. This sudden change can cause serious damage to your engine.

Can an engine overheat only while idle and not when driving?

Yes! Your engine can overheat only when it is idle. This is usually caused by a faulty radiator fan. When you drive, air naturally enters the radiator and helps to cool down the temperature of the coolant but when idle, the radiator fan plays this role because there is no airflow. If this component is faulty, the hot coolant will increase the engine’s temperature and cause overheating.

Can lack of engine oil cause the engine to overheat?

Engine oil lubricates several parts of the engine and ensures they are performing optimally. If there’s no oil in your engine, it will stress the water pump and even the engine. Since there’s no oil to lubricate the engine, the water pump will be working harder and might break down. When the water pump breaks and there’s no oil, the engine will overheat.

How often should you replace your coolant?

The frequency of replacing the coolant in your reservoir varies depending on your car model, make, age, type, and quality of coolant. However, the average time to change your coolant is between 2 years or 30,000 miles to 4 years 60,000 miles.

Can a bad radiator cap result in overheating problems?

The function of the radiator is to maintain adequate pressure in the engine to prevent damage to the radiator and hoses. If the radiator cap is faulty and fails to maintain the correct pressure in the engine, it will lead to the engine overheating. A loose or damaged radiator cap will permit air into the radiator, this air will subsequently reduce the pressure needed to send coolant from the radiator to the engine.

Is it common for old cars to overheat when idle?

Yes! It is common for old cars to overheat when idling. This happens because most engine components are weak and worn out and will fail often. For instance, a worn-out water pump, radiator fan, hose, or radiator pressure cap will cause overheating problems.