Car Overheating Issues? 9 Common Problems & Solutions

Your car overheating can be a scary event. One day it’s running great, and the next the temperature gauge is pegging in the red danger zone.

Overheating can cause significant damage to the engine and cooling system, leaving you on the side of the road or worse.

We’ve collected the most common problems associated with overheating, so you can attempt to avoid them and have solutions ready if you find they are occurring.

#1 – You Have Low Coolant or No Coolant In the Radiator

Your radiator is a heat exchanger that uses fluid to transport heat from the engine. If your coolant is low or missing, that heat exchange can’t happen. Your car can overheat and cause significant damage to the engine or other components.

How to Fix It

If your coolant is low or otherwise missing from the radiator, you need to turn the car off and allow it to cool down. Once it is cool, you need to refill the radiator and cooling system with the proper coolant for your car.

If your radiator doesn’t have a cap that can be removed, the overflow bottle is likely the spot to fill coolant in.

Once the coolant appears to be full, you will want to leave the radiator or overflow bottle cap off and run the car for a few minutes to ensure all air in the cooling system has been purged out.

#2 – You Find A Coolant Leak

One surefire way to overheat your car engine is to run it with a coolant leak.

There are many connection points between components such as the radiator, water pump, and various coolant hoses. Each one can leak coolant that will eventually cause an overheating condition.

How to Fix It

Leaks can happen for many different reasons. Clamps may not be in the correct placement for a complete seal, and they can also not be tight enough to seal the connection.

Old parts can crack from thermal stresses and weep coolant too. The key to fixing a leak is to find the source, and then act. If a connection is loose, it can be tightened. If a part has cracked or broken, it should be replaced.

#3 – Your Engine Has A Bad Temperature Sensor

Your engine may have one or two temperature sensors that send information to a computer and the temperature gauge.

Bad sensors can mislead you and the computer into a false sense of security that everything is operating normally when it isn’t.

Bad sensors can cause many problems that can lead to overheating and significant damage.

How to Fix It

Temperature sensors are used by the engine computer to determine when to adjust the air-fuel mixture, when to turn the cooling fans on, and relay the actual temperature to a gauge in the dash.

A bad sensor may indicate that the engine is warm and cause a poor idling condition in cold weather. A bad sensor can always read a cold condition and prevent the cooling fans from working too. That can lead to overheating and engine damage if the cooling fans never turn on.

Fixing a bad sensor is an easy process.

Most sensors thread into the intake manifold or a cylinder head to read the temperature of the engine coolant. When the engine is cold, you can remove the electrical connector from the sensor and use a wrench or ratchet + socket to loosen the sensor. It should be replaced with a new sensor to return the correct function.

#4 – Your Water Pump Stopped Working

Your engine water pump circulates coolant to transfer heat from the engine to the radiator for thermal dissipation.

If your water pump stops circulating coolant, it can lead to overheating and significant damage.

How to Fix It

There are two types of water pumps: electrical and mechanical.

• Electrical water pumps use electricity to drive the impeller in the water pump housing to circulate coolant.
• Mechanical water pumps use the power from the engine to turn the impeller.

Electric water pumps have an electrical connection to a motor that turns the impeller. The electrical power to the pump could be interrupted due to a blown fuse, a bad relay, or wiring damage.

You can verify the power at the connection with a multimeter and then trace the source of the interruption. If the pump has power but doesn’t work, it may need to be replaced with a new unit.

Mechanical pumps are usually driven by a belt on the engine. It could be one large serpentine belt that runs all accessories on the engine, or a separate belt dedicated to only the water pump. If the belt is damaged, it may not turn the water pump pulley. You can replace the belt or water pump to return the coolant circulation.

#5 – Your Radiator Or Heater Core Has A Problem

The radiator and heater core in your cooling system transfers coolant from one side to another to allow heat to dissipate during that movement.

Each tank on the sides of the radiator has connections to coolant hoses that allow coolant to flow from the engine and back to the engine.

If the radiator has any problems containing or circulating the coolant in the system, it can lead to overheating.

How to Fix It

The radiator is a simple design that is intended to circulate coolant from one end tank to the other. One side brings hot coolant in from the engine, and the other sends cool coolant back to the engine.

Each side of the radiator has a connection to a coolant hose that can leak due to a loose clamp or a broken fitting. There may also be connections to an overflow bottle and other accessories using clamps.

The radiator itself can develop a clog over time due to corrosion and dirt in the coolant. Using regular water that contains minerals can lead to corrosion, and a clog can build enough pressure in the radiator to cause a crack to form. Clogs and cracks can damage the radiator, which will need to be replaced with a refurbished or new unit.

The heater core is a similar design to the main radiator, and it dissipates heat into the passenger cabin for your comfort.

The heater core can become clogged and prevent your car from heating the passenger cabin in cold weather, but it rarely will cause your car to overheat due to a clog. A leak however can drain your cooling system and cause overheating.

Coolant hoses with cracks or holes, broken connectors, and compromised radiators can leak coolant to cause an overheating condition. Damaged components need to be replaced to prevent overheating, and then the coolant should be refilled.

#6 – Your Thermostat Is Stuck Open Or Closed

The thermostat in your cooling system manages the speed at which the coolant circulates.

A closed thermostat restricts the circulation and prevents coolant from flowing through the engine. An open thermostat allows the coolant to flow too fast through the system and it doesn’t dissipate heat from the radiator.

In either case, the engine can overheat and cause significant damage.

How to Fix it

Thermostats are normally closed when they are cold, and they open as the temperature rises. Corrosion is the most likely cause of a thermostat going bad, meaning it always stays closed or open.

A thermostat can be tested for function by removing it from the car and placing it in boiling water. Water boils around 212°F, and a thermostat should transition from closed to open when it is placed in hot water.

If it doesn’t function correctly, it should be replaced with a new one. You can also test the new one in a similar manner before installing it in the cooling system to ensure you are restoring the function.

#7 – You Have A Faulty Cooling Fan

There are two types of cooling fans: electrical and mechanical.

Electrical fans are powered by electricity while mechanical fans are powered by physical contact with a belt. A cooling fan that doesn’t assist in airflow through the radiator can cause an overheating condition.

How to Fix It

Electrical fans are engaged by a relay transferring power to the fan assembly. The power can be interrupted because of a blown fuse or damage to the wiring assembly.

Electrical fans are very reliable, so if they stop working you need to verify that they are receiving power before choosing to replace them.

A mechanical fan assembly has a clutch that engages due to temperature change. The engine accessory belt turns a pulley connected to the fan assembly, and when the clutch engages it will then turn the fan to assist in cooling through the radiator.

If the fan has damaged blades, or the clutch wears out, the fan won’t provide sufficient cooling and the car can overheat.

Any of the mentioned components can be damaged or become worn out, and they should be replaced with new units.

#8 – You Have A Bad Engine Control Unit

Your engine control unit (ECU) monitors and controls the functions related to the engine. That includes the combustion process and the cooling system function.

A bad ECU can misread signals from sensors and not react appropriately. It may not recognize a hot engine and turn the cooling fans on for extra cooling which can lead to overheating.

How to Fix It

The ECU is a complex unit with multiple functions. It can be damaged due to power overloads from jump-starting your car, corrosion on the circuit boards, or physical damage from an impact.

Most ECUs are not easily serviced as their housings are sealed from the elements to prevent damage and corrosion.

If you can prove the ECU is bad, it should be replaced with a quality used or a new control unit. In the case that neither are available, you may find a service that will repair your original unit back to new condition.

#9 – You Have a Blown Head Gasket

One of the worst problems associated with overheating is a blown cylinder head gasket. This gasket is located between the cylinder head and the engine block, and it is meant to seal the combustion chamber.

A bad head gasket can allow coolant to leak into the combustion chamber, and as with any leak, it can cause overheating.

How to Fix It

You may never recognize a bad head gasket if the coolant leaks into the combustion chamber.

If coolant is burned in the combustion process, you may see white smoke emanating from the exhaust pipe. It should also have a sweet smell. Your coolant may turn brown, and the oil could become milky if the bad head gasket allows these fluids to mix.

If you find any of these symptoms, the cylinder head must be removed, and the gasket replaced.

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