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Hi, I'm Azim Uddin, a student who loves cars. Visit carcaresite.com to learn about car maintenance for beginners and experts. In my studies, I found a cool connection between hosting and car care. Join me on this journey where every road has a story, and hospitality meets the thrill of cars. Explore, learn, and enjoy the ride with me!
Last Updated on May 10, 2024 by Azim Uddin
When driving the car, higher airflow helps keep the engine cooler. So, the car can often overheat when idle. But sometimes, the situation is completely opposite. The car starts overheating when driving.
So, why car overheat when driving but not idling? Your car can overheat when driving if there are air bubbles in the cooling system. If the radiator fan is broken or the head gasket is blown, the same problem can happen. Low coolant levels, faulty thermostats, and bad water pumps can also contribute to the problem.
You will learn how to identify the reasons behind the problem and solve them effectively. Continue reading.
Car Overheats When Driving But Not Idling
Here are the reasons for your car overheating when driving. Check the symptoms and solutions.
1. The Head Gasket Is Blown
Head gaskets in your car separate various fluids, such as fuel, engine oil, and coolant. Over time, the head gasket can deteriorate and develop cracks. As a result, the seal between the cylinder head and the combustion chamber will be compromised.
It results in coolant leaks, fuel contamination, and other problems. Due to this reason, the engine starts overheating when driving. As the engine load is low when idling, the car won’t usually overheat in that situation.
Symptoms
- If the head gaskets are blown, you will notice a loss of power.
- There can be white smoke with a sweet smell from the exhaust.
- You may notice steams from under the hood.
Step-By-Step Solutions
- You need to seal the head gasket as a temporary solution. Various head gasket sealers are available out there. You can pour the sealers into the radiator, and they will seal the head gasket.
Then, drive to the closest repair shop and get the head gaskets replaced. It will cost about $1,000-1,500, including parts and labor costs.
2. The Cooling System Isn’t Airtight
There should be no air bubbles in the system for the coolant to work properly. The boiling point of the coolant is usually higher than the operating temperature of the engine. But when air enters the cooling system through a faulty pressure cap or other broken parts, it reduces the coolant’s boiling point.
As a result, the coolant vaporizes and can’t effectively dissipate heat. It causes the car to overheat, especially when driving. While idling, the engine temperature remains normal.
Symptoms
- Sudden spikes in the engine temperature gauge on the dashboard indicate air bubbles.
- The engine mostly overheats at high speeds.
Step-By-Step Solutions
- Turn the car off and let it cool down. Then, open the coolant reservoir cap.
- Top it off with fresh coolant so that the coolant level is close to the brim.
- Ask one of your friends to start the engine and let it idle for a few minutes. Then, they should rev the engine at about 3,000-4,000 RPM.
- Carefully open the bleed valve. It will let the trapped air out. You may see some of the coolant spilling outside.
- After bleeding, fill the reservoir with coolant again. Then, close the cap and let the engine run normally.
Bleeding will remove the air bubbles from the system, and the car won’t overheat anymore.
3. The Thermostat Is Faulty
Thermostats control the flow of the coolant throughout the engine. Sometimes, the thermostat valve may be partially open. It will only let a small amount of coolant flow to the radiator. This is enough to cool the engine when the car is idling.
But when driving, the reduced flow of coolant will cause the car to overheat.
Symptoms
- The engine temperature will rise depending on the engine load.
- Hissing sounds can come from the radiator hose.
Step-By-Step Solutions
- You should check if the coolant is flowing to the radiator normally. Locate the thermostat at the end of the top radiator hose.
- Then, touch the radiator hose, wearing gloves, and tell someone to turn the engine on.
- Check if warm coolant is flowing through the hose. If not, the thermostat is faulty.
You should take the car to a repair shop and get it replaced. It will cost about $150-250, including parts and labor costs.
4. The Water Pump Is Faulty Or Broken
The water pump circulates the coolant through the engine. If the pump is clogged or broken, it won’t be able to circulate the coolant properly. As a result, the car will overheat when driving.
Symptoms
- No overheating signs will appear when idling. But as soon as you start driving, the car will overheat. It happens even at low speeds.
- There can be signs of coolant leaks close to the water pump.
Step-By-Step Solutions
- You should get the water pump replaced by an experienced mechanic.
It may cost about $500-1,000, including parts and labor.
5. The Radiator Fan Is Broken
Radiator fans help dissipate heat better. If the fan blades are broken, they won’t blow cool air into the radiator as efficiently. This might be okay while idling. But, the car will overheat while driving due to the lack of airflow.
Symptoms
- There can be grinding noises from the radiator fan.
- When the car runs at high speeds, the engine won’t overheat.
Step-By-Step Solution
- You need to inspect the radiator fan visually. If there are signs of broken blades, you should replace the fan.
Remove the wiring harness from the radiator fan and take it off the mount. Then, install a new fan and connect the wiring harness.
Can low oil cause overheating?
Insufficient oil levels can indeed lead to a cascade of problems, potentially causing more than just overheating. Oil serves as a vital lubricant for the engine’s components, ensuring they operate smoothly.
The absence of an adequate oil supply imposes stress on the engine, with repercussions that extend beyond mere overheating. When facing low oil levels, the water pump, a key element in the cooling system, is forced to operate at an increased intensity. This heightened workload on the water pump can result in overheating, jeopardizing the engine’s overall functionality.
In essence, the phrase “low oil cause overheating” encapsulates the domino effect that insufficient oil levels can trigger within a vehicle’s intricate machinery.
FAQs
Many people also ask the following questions. Check the answers.
Q: Can I drive a car if it overheats when driving but not idling?
You can, but that is only for a short distance. Driving an overheating car for a long time can damage crucial engine components.
Q: Can I keep the car idle to reduce overheating?
If the car overheats while driving, keeping it idle isn’t the right solution. You should pull it over and check the reason.
Q: What will be the engine temperature if the car overheats when driving?
The normal operating temperature of the engine is about 195-220 degrees Fahrenheit. If the engine overheats, the temperature will go above 230 degrees Fahrenheit.
Conclusion
The engine has a higher load when driving a car compared to when idling. However, the airflow is also higher in this condition. In some situations, the car overheats when driving but not idling.
Its main reasons are blown head gaskets, faulty thermostats, broken water pumps, air bubbles, and broken radiator fans. Once you know the symptoms, it will be easier for you to identify the reason. Then, you can take the right steps to solve the problem.
