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Car Overheating When Idle? Here Are 7 Reasons Why (+What to Do)

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You’re stuck in a horrible traffic jam. Sitting in the driver’s seat, you notice the temperature gauge slowly creeping up to red. But when you start driving, the temperature goes back down.

What’s going on? 
Well, that’s what a car overheating when idle looks like, and it happens for several reasons.

Fret not!
In this article, we’ll discuss why it can happen, what to do when your car overheats, and answer some FAQs

This Article Contains:

Let’s get started!

Is Your Car Overheating When Idle? Here Are 7 Possible Reasons

A car overheats when idle for many reasons — mostly related to an issue with the engine’s internal system (coolant system or engine components). 

Although low coolant level seems to be the main culprit behind a raised temp gauge, here are some other reasons for an overheating problem when idle:

1. Bad Thermostat

Your car’s thermostat detects the engine coolant temperature and controls coolant flow. When the engine reaches optimum working temperature, the valve opens up, and hot coolant flows out of the engine and into the radiator.

When you have a bad thermostat, it may not function or open the valve at higher temperatures. If the thermostat valve is stuck, it restricts coolant flow and reduces cooling efficiency.

2. Bad Radiator Cap

The radiator cap in your car adjusts the pressure in the radiator to prevent pressure build-up. It does so by releasing excess pressure (to lower the internal pressure) or letting air in (when the coolant system cools down). 

A bad radiator cap causes a pressure build-up in the cooling system — the opposite of how it should work. Extremely high pressures cause the engine coolant temperature to rise and boil — which is dangerous. This overheating problem can damage the radiator, water hose, plastic coolant reservoir, and engine block. 

That’s a very costly repair job you’re looking at…

3. Clogged Radiator

Dirt, dust, and debris can get stuck between the radiator fins or the fan blades, causing a clogged radiator. If the blockage is significant, it can affect your fan motor, restricting airflow and causing slower engine cool down — especially when idle.

Let’s say a small plastic bag gets stuck in the radiator. In new vehicles, the electric fan would come on immediately, pulling air into the radiator. But, if the blockage is large enough to disrupt fans from working, engine overheat may occur, and you’ll see a spike in your temp gauge. 

When you start driving again, the debris might get dislodged, and the engine cools down.

4. Malfunctioning Radiator Fan

The radiator fan blows air over the radiator, which helps lower the coolant temperature. It activates once the engine is at optimum temperature and when idle. 

You can easily suspect a faulty radiator fan if your car overheats when idle or in stop-and-go traffic. Here are some possible radiator fan issues:

5. Failing Head Gasket

A failed or blown head gasket can cause your car’s temperature to rise when idle. The head gasket prevents high-pressure fluids in the engine block (combusted fuel, water, and engine oil) from mixing.

When idling, the engine relies on coolant water to cool it down. But a blown head gasket causes the coolant to flow into the engine block and get combusted. You’ll also notice that the coolant level drops and the engine overheats.

6. Bad Water Pump

The water pump creates pressure that pumps water through the engine when idle or moving. 

If the water pump fails or is blocked, the pressure created isn’t enough to push the water through. Less water will reach the engine, heat will accumulate, and the temperature will rise.

Besides an overheating engine, a bad water pump can cause a loud whining noise.

7. Coolant Issues

Lastly, issues with the coolant could cause an overheating engine when idle. 

Coolant is vital for your engine, as it keeps the temperature low and prevents overheating. It circulates throughout the cooling system and absorbs heat from the engine. 

If something’s wrong with the coolant, your engine is at risk of more than just overheating. 

Here are a few examples of what can go wrong with coolant water:

So, now you know what could cause a car’s temperature to rise when idle. 
But do you know what you should do when your car overheats?

Let’s look into that.

Do’s and Don’ts When Your Car Overheats

It’s understandable that a road emergency can induce panic and make our brains fail to work properly. We get it. With that, we’ve compiled a list of do’s and don’ts to remember when your car overheats.

DO

Here are the things that you should do if your car is overheating:

DON’T

Now let’s look at the things you shouldn’t do with an overheating  engine:

Experiencing an overheated engine while driving is scary, but if you remain calm and stick to our list, you should be able to save your car from expensive repairs.

Now time to answer some FAQs.

6 FAQs on Engine Overheating

Here are the answers to some commonly asked questions about engine overheating:

1. How Do I Prevent My Car’s Engine From Overheating?

Preventing your car from overheating is straightforward. 
Here are some things you can do to avoid a high engine temp when idle:

2. Can Overheating Seize My Car Engine?

Yes, it definitely can.
But most moving components, like the pistons, will malfunction before the engine stops functioning completely. If this happens, you’ll have to replace the whole engine and everything else connected.

3. What Are the Signs of Overheating?

Here’s what overheating could look like: 

4. Are Old Cars Supposed to Overheat When Idle?

Technically, yes. 
Older engines tend to overheat because it’s hard for the cooling system to maintain operating temperature. This is caused by the old and weak engine components they may still have.

But regardless of whether it’s an old model or not, frequently overheating when idle is a bad sign. So it’s best to immediately contact your mechanic to get it looked at.

5. Can the Lack Of Engine Oil Cause Overheating?

Lack of engine oil CAN cause the car’s temperature to rise. 

Engine oil does more than keep your engine lubricated— it also helps prevent overheating.

It lowers the heat released during combustion by reducing the friction produced. As friction produces heat — when there’s less friction in the engine, less heat is released. Engine oil also helps remove a small amount of heat as it flows through the engine.

6. What Is Considered Optimal Engine Temperature?

The optimal operating temperature is around 195°F – 220°F (75°C – 105°C). If your engine’s temperature is below or above this range, performance could be disrupted.

Final Thoughts

A car overheating when idle is a major indicator that something’s wrong with the cooling system. There are many reasons why this could happen, like a broken radiator fan, thermostat, or temperature gauge.

That being said, it’s best to get your vehicle checked by a professional — like AutoNation Mobile Service!

AutoNation Mobile Service is a mobile auto repair service you can get with a quick tap on your device. We offer various mobile repair services, and our mechanics are available 7 days a week.

What are you waiting for? 
Contact us today, and we’ll send our best mechanic to get your engine looked at right away!