ENGINE OVERHEATING GUIDE
Why Is My Car Overheating?
A car can overheat when the cooling system can no longer remove enough heat from the engine. Common causes include low coolant, coolant leaks, thermostat problems, cooling-fan failures, water-pump problems, radiator restrictions, and other cooling-system faults.
Overheating should be taken seriously. Continuing to drive an overheating vehicle can turn a cooling-system problem into much more expensive engine damage.
The temperature gauge or warning message tells you that the engine is getting too hot, but it does not identify which component has failed. The cooling system should be inspected and tested before parts are replaced.
8 Common Causes of Car Overheating
1. Low Coolant
Low coolant is one of the first things to consider when an engine begins overheating.
The cooling system relies on the proper amount of coolant to absorb heat from the engine and transfer that heat to the radiator.
If the coolant level becomes too low, the system may not be able to control engine temperature properly.
However, coolant normally operates inside a closed system. If the coolant level keeps dropping, the important question is why.
2. Coolant Leak
A coolant leak can gradually lower the coolant level until the engine begins running hotter than normal.
Possible leak locations include:
- Radiator hoses
- Radiator
- Thermostat housing
- Water pump
- Coolant reservoir
- Heater hoses
- Cooling-system fittings and connections
- Other engine cooling passages or components
Some leaks leave an obvious puddle underneath the vehicle. Others may only leak when the system is hot and pressurized, making them more difficult to locate.
3. Bad Thermostat
The thermostat regulates coolant flow between the engine and radiator as the engine reaches operating temperature.
If the thermostat does not open correctly, coolant circulation through the radiator can be restricted and engine temperature can rise quickly.
A thermostat problem can sometimes cause overheating that appears suddenly even when the coolant level initially looks normal.
4. Cooling Fan Problem
The radiator cooling fan helps move air through the radiator when natural airflow is not sufficient, especially while the vehicle is stopped or moving slowly.
A failed fan motor, relay, fuse, wiring problem, control problem, or temperature-related fault can prevent the fan from operating when needed.
This is one reason a vehicle may stay near normal temperature while moving but begin overheating while sitting in traffic or idling.
5. Water Pump Problem
The water pump circulates coolant through the engine, radiator, and cooling system.
A water pump can develop an external leak, bearing problem, or internal circulation problem depending on its design and failure mode.
Because water-pump problems do not always present the same way, testing and inspection are important before determining that the pump needs replacement.
6. Radiator Problem
The radiator transfers heat from the engine coolant to the outside air.
Restricted coolant flow, damaged radiator fins, external blockage, internal restriction, or another radiator problem can reduce the system’s ability to remove heat.
A radiator problem can sometimes look similar to a thermostat, fan, or circulation problem, which is why the complete cooling system should be considered during diagnosis.
7. Cooling-System Pressure Problem
Automotive cooling systems operate under pressure. Proper system pressure helps the coolant operate at the temperatures required by the engine.
A leaking pressure cap, damaged reservoir, hose problem, or another pressure-related fault can affect cooling-system performance or allow coolant to escape.
8. Internal Engine Problem
Not every overheating problem is caused by an external cooling-system component.
In some cases, an internal engine problem can allow combustion pressure, coolant, or engine oil to move where it should not.
Internal engine problems require proper testing. Overheating by itself is not enough to conclude that an engine has a failed head gasket or another major internal failure.
ENGINE TEMPERATURE RISING?
Do not keep driving an overheating vehicle hoping it will cool down.
Continued overheating can increase the risk of cylinder-head damage, head-gasket failure, engine damage, and other expensive repairs.
Why Does My Car Overheat While Idling but Cool Down While Driving?
If the engine temperature rises while sitting still or moving slowly but improves once the vehicle begins moving, radiator airflow should be considered.
At road speed, outside air naturally moves through the radiator. At idle, the vehicle depends much more heavily on its electric or mechanical cooling fan to provide airflow.
A cooling-fan problem is therefore one possible cause of overheating at idle.
However, low coolant, circulation problems, radiator restrictions, and other faults can produce similar symptoms, so the fan should not automatically be replaced based on this symptom alone.
Why Does My Car Overheat While Driving?
Overheating while driving can be caused by low coolant, coolant loss, restricted coolant circulation, thermostat problems, water-pump problems, radiator restrictions, or other cooling-system faults.
The driving conditions can also provide useful diagnostic information. Note whether the overheating happens during highway driving, acceleration, stop-and-go traffic, or only after the engine has been running for a certain amount of time.
Why Is My Car Overheating With Coolant in It?
Having coolant in the reservoir does not prove that the cooling system is operating correctly.
The engine can still overheat because of a thermostat problem, inadequate coolant circulation, cooling-fan failure, radiator restriction, pressure problem, trapped air, or another fault.
The coolant level is only one part of cooling-system diagnosis.
Why Is My Car Losing Coolant?
If coolant needs to be added repeatedly, the cooling system should be inspected for the reason it is losing coolant.
Leaks can be obvious or very small. Some only become visible when the engine reaches operating temperature and the cooling system becomes pressurized.
Simply continuing to refill the reservoir may allow the underlying problem to worsen.
Can a Bad Thermostat Cause Overheating?
Yes. If a thermostat remains closed or does not open sufficiently, coolant flow through the radiator can be restricted and engine temperature may rise.
But thermostat replacement should not be based only on the fact that the engine overheated. Low coolant, leaks, fan problems, circulation problems, and other faults should also be considered.
Can a Bad Water Pump Cause Overheating?
Yes. Because the water pump is responsible for circulating coolant, a water-pump problem can contribute to overheating.
Some failed water pumps leak externally. Others may develop bearing or circulation problems. The symptoms depend on the pump design and the type of failure.
Can a Bad Cooling Fan Cause Overheating?
Yes. A cooling fan that does not operate when commanded can reduce airflow through the radiator, particularly when the vehicle is stopped or traveling at low speed.
Cooling-fan operation can involve the fan itself as well as fuses, relays, wiring, sensors, control modules, and other electrical components.
If electrical testing is needed, learn more about
Rexroad’s mobile advanced diagnostic service.
Why Does My A/C Get Warm When the Engine Is Overheating?
The engine cooling system and air-conditioning system are separate systems, but some components and operating conditions can affect both.
For example, inadequate airflow through the condenser and radiator can contribute to poor A/C performance and cooling-system problems, particularly while the vehicle is stopped.
Some vehicles may also reduce or disable A/C compressor operation when engine temperature becomes excessive.
If the primary complaint is warm air from the vents rather than high engine temperature, read
about Rexroad’s mobile A/C service.
What Should You Do if Your Car Starts Overheating?
If the temperature gauge climbs into the hot range or an overheating warning appears, avoid continuing to drive unnecessarily.
If it is safe to do so, get the vehicle to a safe location and shut the engine off.
Do not remove a radiator cap or pressurized cooling-system cap while the system is hot. Hot coolant can be under significant pressure and can cause serious burns.
Allow the vehicle to cool before inspecting the cooling system.
Can You Drive a Car That Is Overheating?
Continuing to drive an overheating vehicle can cause additional damage.
How quickly damage occurs depends on the cause and severity of the overheating, but there is no reliable safe distance to continue driving once an engine is overheating.
Severe overheating can damage cylinder heads, head gaskets, engine components, seals, and other parts.
If the temperature is continuing to rise, the safer approach is to stop driving and determine why the engine is overheating.
SAFETY NOTE
Never open a hot pressurized cooling system.
Wait for the engine and cooling system to cool before removing a radiator or coolant-system pressure cap.
How Is an Overheating Problem Diagnosed?
Diagnosis starts with the symptoms and conditions under which the vehicle overheats.
Depending on the problem, cooling-system diagnosis may include:
- Checking coolant level and condition
- Inspecting for visible coolant leaks
- Cooling-system pressure testing when appropriate
- Inspecting radiator and coolant hoses
- Checking thermostat operation
- Checking cooling-fan operation
- Testing fan electrical circuits when necessary
- Inspecting the water pump for signs of failure
- Checking coolant circulation and radiator performance
- Additional testing when an internal engine problem is suspected
The objective is to identify why the vehicle is overheating before recommending a repair.
Mobile Cooling System Repair in Frisco, TX
Rexroad Mobile Auto Repair provides mobile cooling-system diagnosis and eligible repairs in Frisco and nearby communities.
Depending on the vehicle and confirmed failure, mobile cooling-system service may include:
- Coolant leak diagnosis
- Radiator-hose replacement
- Thermostat replacement
- Cooling-fan diagnosis and eligible repair
- Water-pump diagnosis and eligible replacement
- Radiator and cooling-system inspection
- Overheating diagnosis
Learn more about Rexroad’s mobile cooling system service →
You can also
view all Rexroad mobile auto repair services
or learn more about
mobile mechanic service in Frisco, TX.
CAR OVERHEATING?
Tell me exactly what the vehicle is doing.
Include the year, make, model, temperature-gauge behavior, warning lights, visible coolant leaks, when the overheating occurs, and your vehicle location.
Call 469-469-4521
or submit a service request online.