When operating normally, engine temperatures can go up to 220°F. While idling, the engine temperature should be about 195°F. The engine can overheat if it has excessive load.
But sometimes, you may notice the car overheating while idling. It happens if the coolant level is low the coolant is contaminated, and the thermostat is malfunctioning. Cooling system issues and faulty head gaskets can also contribute to the problem. You need to diagnose the reason and take effective steps to solve the problem.
I will discuss the reasons and symptoms of this problem. You will also learn how to solve these problems in easy steps. Let’s begin.
Car Overheating While Idling: Reasons Explained in Detail
Normally, a car shouldn’t overheat when idle. If it happens, the following reasons may be there.
1. Low Coolant Level or Contaminated Coolant
The coolant in your car absorbs heat from the engine and transfers it to the environment. A mixture of antifreeze and water is used as a coolant. Its level should be up to the FULL or MAX mark on the reservoir. If the level is low, the heat dissipation will not be enough. So, the car will overheat even if it is idle.
Sometimes, hard water and other debris can cause the coolant to get contaminated. The contamination reduces the thermal efficiency of the coolant, which causes the car to overheat.
Other Symptoms
- The engine temperature gauge on the dashboard will rise.
- There will be low coolant warning in modern cars.
How Do You Solve the Problem?
- Check the coolant level. If it is lower than normal, top it off. Also, check for coolant leaks and fix the leaks before refilling the coolant.
- If there is brown sludge in the coolant or the reservoir is dirty, you need to flush the cooling system. Drain the coolant first and then flush the system with water.
After that, refill the system with fresh coolant.
2. Thermostat Malfunction
Depending on the temperature of the engine coolant, the thermostat allows or restricts it from flowing to the radiator. But if the thermostat is malfunctioning, it may prevent the coolant from flowing.
As a result, the car will overheat when idling. The buildup of dust and debris can cause the thermostat valve to get stuck.
Other Symptoms
- There will be low or no coolant in the radiator.
- The car will overheat quickly, even when the engine RPM is the lowest.
How Do You Solve the Problem?
- Locate the thermostat first. Follow the upper hose of the radiator, and the thermostat will be at the end of the hose.
- Keep your hands on the upper hose near the thermostat. Ask someone to start the engine. After the engine starts, you should feel the upper radiator hose becoming warm.
- But if there is no flow of warm coolant through the hose, the thermostat is faulty.
You should take the car to a repair shop and get the thermostat replaced. It will cost about $150-250, including parts and labor.
3. Cooling System Issues
You should expect at least one or more cooling system issues. The cooling system of your car has multiple components, such as the radiator, pressure cap, water pump, hose, radiator fan, etc.
Various problems can arise with these components. For example, the radiator may get clogged over time, which will cause the car to overheat. A faulty radiator fan or leaky pressure cap can also be responsible. Water pumps can be faulty or broken. Coolant hoses can also be cracked.
Other Symptoms
- You may notice unusual noise from broken fans or pumps and steam or coolant leaks from the system.
How Do You Solve It?
- Inspect each of the cooling system components separately.
- The radiator should not have any clogs, and the fans should work properly.
Also, the radiator pressure cap should be tight. It is better to take the car to a repair shop and get the whole system checked by an expert.
4. Faulty Head Gaskets
Head gaskets in the car work as a seal between the cylinder head and the combustion chamber. It keeps the coolant from mixing with the fuel or engine oil. Over time, these rubber gaskets can become brittle and crack due to engine overheating.
In that case, the coolant will leak into the combustion chamber and be burnt inside the engine. So, the cooling performance will be reduced. The car will overheat while idling or running at a low speed.
Other Symptoms
Besides overheating symptoms, you will get a sweet smell from the exhaust. It is caused by the burnt coolant.
How Do You Solve the Problem?
- You should turn the engine off and let the engine cool completely. Then, you can use a head gasket sealer to seal the gasket temporarily. These liquids can be poured into the radiator.
- For a permanent fix, you should take the car to a repair shop and get the head gasket replaced. It can cost about $1,000-1,500, including parts and labor.
Tips to Prevent Car From Overheating When Idling
Follow these tips to get rid of the overheating problem.
- If the car overheats when idling with the AC on, turn it off. Then, crank the heater up. It will draw some heat away.
- Unless it is urgent, don’t turn the air conditioner on while idling.
- Don’t pour water directly onto the engine to cool it down.
FAQs
Checking the following answers to frequently asked questions may be helpful.
Q: Why is my engine overheating, but the coolant is full?
The engine can overheat due to a faulty thermostat or broken radiator fans, even if the coolant is full. Overloading the engine can also cause the problem.
Q: Can a car overheat from idling too long?
Yes. Idling for 15 minutes or more can cause a car to overheat. The airflow is better when the car is running.
Q: Should I drive if the car overheats when idling?
Driving at low speeds may be possible. But I suggest you stop driving and diagnose the reason.
Final Words
A common misconception about car overheating is it can only happen when the car is running. When people see a car overheating while idling, they get confused. But it can happen for many reasons.
Low coolant levels, coolant leaks, blown head gaskets, faulty thermostats, broken radiator fans, etc., are common reasons for cars overheating when idling. I provided the most effective solutions so that you can address the issue promptly.