Car Engine Overheating Problems – Causes & Fixes

For most people, the engine is the most important part of their vehicle. That’s why it can be quite concerning if your car’s engine starts to overheat — especially if you’re behind the wheel when it happens. Unfortunately, engine overheating is one of the most common problems for car owners and, if not properly diagnosed and corrected, the problem can turn catastrophic. Today, we’re looking at the top 10 most likely causes for engine overheating, as well as their most common solutions. Read on to learn what to do when your car’s engine starts overheating. 

Why Is My Car Engine Overheating and is it Bad?

There are many different reasons a car engine can overheat, and sometimes the consequences can be catastrophic. When manufacturers design engines, they do so with a specific operating temperature in mind. If the engine is consistently operating when it’s too cold, performance will suffer and components will likely have increased wear. In contrast, if an engine is consistently operated when it’s too hot, performance can also suffer and the engine can begin to experience internal problems. 

In addition to the engine itself, other parts connected to or working with the engine can also experience failure if the temperature gets too hot. This includes but is not limited to intake and exhaust manifolds, emissions systems, and turbochargers or superchargers.

As an engine begins to overheat, it also starts to rapidly break down the oil. This is known as oil shearing, and causes the oil to lose viscosity, which reduces its ability to properly lubricate. Ultimately, if an engine gets too hot and burns up its oil, it can experience catastrophic failure. In the worst case scenario, this can mean the melting of internal components, like pistons and connecting rods, to even cracking or melting the engine block itself. 

The part of the car that controls the temperature of the engine is known as the “cooling system.” The cooling system consists of several parts, including the radiator, water pump, cooling fans, coolant, and thermostat. If any of these parts starts to malfunction or fail, the engine can quickly start to overheat. That’s why it’s important to always make sure the engine’s cooling system is in tip-top shape, and that there is always enough coolant and oil in the engine. 

Top 10 Causes of Engine Overheating

• Cause #1 for a Car Overheating – Coolant Levels
• Cause #2 for Why a Car Overheats – Oil Levels
• Cause #3 for What Causes a Car to Overheat – Cooling System
• Cause #4 for an Engine Overheating – Radiator Cap
• Cause #5 for Why Cars Overheat – Cooling Fan
• Cause #6 for a Car Overheating – Coolant Temperature Sensor
• Cause #7 for Why a Car Overheats – Water Pump
• Cause #8 for What Causes an Engine to Overheat – Thermostat
• Cause #9 for an Engine Overheating – Radiator
• Cause #10 for Why Cars Overheat – Head Gasket

1) Low Coolant Levels

The most common cause of an overheating engine is low coolant level. Coolant is the most vital part of the cooling system. Coolant is part antifreeze (ethylene glycol) and part water, and it circulates around the radiator and engine block. The purpose of coolant is to reduce the temperature of the engine block by circulating through its coolant passages. If there is not enough coolant in the system, it will not be able to sufficiently cool the engine. 

There are two primary ways coolant can be lost from an engine, either through an external or an internal leak. Externally, there are several areas the coolant can leak from, such as the radiator, radiator hose, or radiator cap. Internally, the most common spot is for coolant to leak through the head gasket. Additionally, coolant can also evaporate in small amounts if the environmental conditions are extremely hot.

The easiest way to check coolant levels is by looking at the coolant reservoir under the hood. If the coolant is between the Full and Low lines you are good to go. If there is not enough coolant, make sure to add more right away. 

2) Low Oil Levels

Besides coolant, another common cause of engine overheating is a low oil level. Oil is used to lubricate the internal components of the engine, and it’s probably the most important fluid in the engine. However, if there are low oil levels, or if the oil has sheared too much and lost viscosity, the oil will fail to properly lubricate. This can cause increased friction between the components, which can result in greater internal temperatures.

In addition to the engine overheating, low oil is a serious concern because it can easily lead to a loss of oil pressure. Without oil pressure the engine will immediately seize or catastrophically explode. Like coolant, oil can be lost either externally, through leaking, or internally, through evaporation or by burning. 

The best way to check oil levels is by using the oil dipstick under the hood and ensuring oil is between the full and empty levels. If there is not enough oil, make sure to add more right away.

3) Cooling System Leaks

As we mentioned, coolant is the most important part of a car’s cooling system, and any failures in the system can quickly lead to engine overheating. The most common cause of cooling system failure is leaking. Leaks can happen in many places in the system, but they most frequently occur in the radiator or with the radiator hoses. 

If either the radiator or radiator hoses connecting the radiator to the engine become compromised, coolant can leak out of the system. As we explained, that can easily turn into catastrophic engine failure. It’s important to periodically check your radiator and all connections into and out of the engine, to make sure everything is in working order. 

The most efficient way to test the cooling system is by pressurizing it. By unscrewing the radiator cap and pressurizing the system, you can easily spot any potential leaks. If you notice any problems, like a leaking radiator or hoses, make sure to replace them immediately.

4) Radiator Cap Failure

While checking the cooling system for leaks, it’s a good idea to inspect the radiator cap itself for integrity. The radiator cap covers the radiator and stops coolant from leaking or evaporating out into the atmosphere. A leaky cap can cause a bad seal, potentially resulting in increased evaporation, or it can cause the coolant to leak out. 

Radiator caps are relatively inexpensive, so if you notice any problems with yours it’s best to go ahead and replace it. Leaky radiator caps are a common cause of low coolant, which as we’ve noted can be devastating for an engine. 

5) Cooling Fan Failure

One of the key parts of the radiator is the cooling fan(s), and if they fail it can easily lead to engine overheating. The purpose of the radiator is to reduce the temperature of the coolant once it exits the engine. Reducing the coolant’s temperature allows it to re enter the engine so it can take away more of the engine’s heat.

It’s a closed and circular system: Coolant leaves the radiator and enters the engine, circulates through the engine and takes on the engine’s heat, then re enters the radiator to shed all the heat it just took on, then repeat. 

Part of the way the radiator reduces the temperature of the coolant is by using a fan(s). The fan(s) sit in front of the radiator and spin, blowing cold air over the radiator to reduce the coolant’s temperature. If the fans fail to spin the coolant will struggle to stay cool, leading to overheating.

The cause of a failed radiator fan can be either mechanical or electrical. To test that the fan works, turn on your engine and put the A/C on full blast. If the fan does not spin with the A/C on high, you know you have a problem. Your first step is to check all fuses and relays to make sure they are functioning. If they are, the fan’s motor (if it’s electric) may be damaged. You can test the motor by hooking up electrical current to it and seeing if it spins.

Additionally, foreign objects can hit the fans and cause them to sustain damage, which can lead to failure. If you have determined that all fuses/relays are working and the motor works, the problem may be related to the coolant temperature sensor and not the fan itself. 

6) Coolant Temperature Sensor Failure

The coolant temperature sensor is responsible for relaying information from the engine to the ECU about the temperature of the coolant. This tells the thermostat when to open as well as the radiator fans when to turn on.

If the coolant sensor is failing, that means it can fail to accurately relay the engine’s temperature to the ECU. This can cause the radiator fans to not turn on, because the ECU might not realize the engine needs to be cooled down if the readings are wrong. If you suspect your coolant temp sensor might be faulty, you can test them to make sure they still work. However, they are not very expensive to replace, so you might consider just replacing it instead of testing it. 

7) Water Pump Failure

After the radiator fans, another common cause of car engines overheating is water pump failure. The purpose of the water pump is to circulate coolant through the engine and radiator, allowing it to reduce engine temperatures. Unfortunately, even though it is such an important part, many OEMs use incredibly cheap plastic water pumps that are prone to failure (BMW, we’re looking at you). If the water pump fails, the coolant will not be able to circulate through the engine and radiator. This will result in a failure to cool and elevated engine temperatures. 

The easiest way to check for a faulty water pump is to visually inspect the pump itself for leaks. Water pumps have a “weep hole” on the bottom, which will let you know if the internal seals are beginning to fail. Basically, if you notice coolant coming from the weep holes the water pump is faulty. Water pumps are wear items and normally need to be replaced periodically for maintenance, so make sure when it comes time you don’t forget!

8) Thermostat Failure

Another common cause of engine overheating is thermostat failure. The thermostat is part of the cooling system, and its purpose is to help the engine maintain peak operating temperature. When the engine is too cold, the thermostat stops coolant from circulating, allowing the engine to quickly heat up to operating temperature. However, when the engine begins to warm, the thermostat opens to allow coolant to circulate and cool the block. 

Thermostats can fail one of two ways, either being stuck open or closed. If they are stuck closed, coolant will not circulate, causing the engine to overheat. If they are stuck open, the engine can struggle to reach operating temp due to excessive coolant flow. 

The best way to test the thermostat is by inspecting the radiator hose. When the car is cold, turn it on and inspect the hose. If coolant is flowing when the engine is still cold, the thermostat is likely stuck open. In contrast, if the engine gets up to operating temperature and there is no coolant flowing, the thermostat is likely stuck closed. A closed thermostat can be a cause of engine overheating, and replacing the thermostat may solve the problem. 

9) Radiator Failure

As the biggest component of the cooling system, radiator failure is a prime cause of excessive engine heat. The radiator reduces the temperature of the coolant, which allows it to keep the block’s temperatures down. If the radiator fails the entire cooling system will come to a crashing halt.

Several things can cause radiator failure. The most common causes are damage from external objects, like rocks or debris from the road, as well as corrosion. Corrosion can occur in high-mileage radiators that have leaks allowing debris into the system, or in radiators that do not have regular coolant flushes. External objects can cause the coolant passages of the radiator to collapse and become blocked, restricting the flow of coolant. Corrosion can also block the coolant passages. 

To test the radiator, you will want to pressurize the system and see if there are any leaks. You can also visually inspect it to see if there are bent cooling fins or coolant passages. Unfortunately, radiators are not cheap to replace, making it an expensive repair if it happens to be the problem. 

10) Head Gasket Failure

For our final common cause of engines overheating, we’re looking at head gasket failure. The head gasket separates the cylinder head from the engine block. Its purpose is to seal the combustion chamber to make sure it maintains proper compression. If the head gasket fails, coolant can leak out of the engine block and potentially mix with the oil supply. This results in contaminated oil that loses viscosity, as well as low coolant levels.

The most telltale signs of head gasket failure are low coolant, white smoke in the exhaust (from the coolant burning), and milky colored oil from coolant contamination. If you notice these issues together you likely have head gasket failure. Replacing the head gasket is your only solution, and while gaskets are cheap the labor can be very expensive, as the engine has to be taken apart. 

Why Is My Car Engine Overheating Summary

There are many reasons that a car’s engine may be overheating. Most of these are related to failure within the cooling system, which can include the radiator, radiator hoses, radiator cap, radiator fans, water pump, coolant temperature sensor, or the thermostat. 

If your engine starts to overheat, the results can be catastrophic. They are not limited to the internal components melting and the engine block melting or cracking. As you can tell, it’s extremely important to make sure your cooling system is in good shape to make sure your engine stays healthy. 

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