What Causes a Car to Overheat When Idling?

Reviewed by

Anthony Harlin, ASE Certified Master Automobile Technician

Technical Reviewer at CarParts.com

Written by CarParts.com Research Team - Updated on October 16th, 2023

Reading Time: 5 minutes
Summary
  • Cars typically overheat when idling because you’ve been stuck in traffic for too long or if the cooling system is damaged.
  • Broken thermostats and faulty radiator fans may also cause your vehicle to overheat.
  • You can tell if your car is overheating when the temperature gauge has abnormally high readings and if the hood of your vehicle is hotter than normal.

If your car is starting to overheat even when you’re idling, there’s a good chance there’s something wrong with your engine. If you want to know what’s wrong with your vehicle, have a look through some of the most common causes:

  • You’ve been stuck in traffic for too long
  • The cooling system is damaged
  • Your vehicle is running low on coolant
  • There is a coolant leak
  • Your radiator fan is broken
  • The thermostat is malfunctioning

Why Does My Car Overheat When Idling?

There are multiple explanations as to why a car overheats while idling, but not when you drive.

There are multiple explanations as to why a car overheats while idling, but not when you drive. Narrowing down the root cause is tricky, but not impossible. Here are six of the most common causes:

Getting Stuck in Traffic

Believe it or not, idling in traffic for too long can lead to your engine overheating. This may happen if your vehicle is stationary or extremely slow for over 10 to 15 minutes. This is also more likely to happen on hot days.

Leaving your AC running may contribute to this problem because the car’s AC forces the engine to work harder. These factors combined can make the engine overheat very quickly. A simple solution would be to turn off the AC in hopes of lowering the temperature of the engine, but if this does little to help, you might have a more serious problem on your hands.

Malfunctioning Cooling System

If your car overheats at idle, another potential cause could be a faulty cooling system. A bad radiator cap or a clogged radiator may cause the system to malfunction and cause the engine to overheat due to the buildup of pressure. A failing electric fan or fan clutch will also cause the cooling system to malfunction because the radiator won’t receive enough cool air.

The higher the pressure inside the cooling system, the higher the temperature of the engine coolant. Be cautious as boiling coolant is dangerous for your vehicle. It’s a problem that can potentially destroy your radiator, water hose, coolant reservoir, and engine block.

Low On Coolant

A vehicle that’s low on coolant might not be able to regulate the temperature of its engine properly. Because of this, you need to make sure to refill your coolant as recommended by your vehicle manufacturer. Never drive with an empty coolant reservoir because that will make your vehicle’s engine more likely to overheat.

Coolant Leaks

Another common cause for cars overheating while idle is coolant leaks. Since coolant is necessary to regulate the temperature of the engine, it’s understandable that a leak can cause the engine to overheat. These leaks are usually caused by blown head gaskets and leaky radiator caps. However, coolant leaks could also be caused by water pump leaks, damaged hoses, or a faulty heater control valve.

It’s a good practice to check your engine regularly so you can spot any parts that look damaged or faulty. Be sure to get any weathered parts replaced or repaired immediately because neglecting sensitive components like these could potentially destroy your engine.

Faulty Radiator Fan

If your car tends to overheat, there might be something wrong with your radiator fan. Radiator fan malfunction is often caused by blown-out fuses, a faulty motor fan, and damaged wires.

Broken Thermostat

Last but not least, a car with an engine that overheats at idle could potentially have a broken thermostat.

A broken thermostat won’t be able to recognize when the engine gets too hot, causing it to block the flow of coolant when it shouldn’t.

How Can You Tell If Your Car Is Overheating?

Two of the biggest indicators that your car is overheating is if the temperature gauge has abnormally high readings, and if the hood of your vehicle is extraordinarily hot. While the engine is running, touch the hood of your vehicle. If you’re unable to touch the vehicle for more than a few seconds, it might be time to bring it to an expert.

Two of the biggest indicators that your car is overheating is if the temperature gauge has abnormally high readings, and if the hood of your vehicle is extraordinarily hot.

Anthony Harlin, ASE Certified Master Automobile Technician

Another indicator is rising smoke or steam from your engine. The engine isn’t supposed to release any fumes. The presence of smoke is a sign that the coolant in your engine has reached a boiling point, turning into a gas that creates pressure in the cooling system.

What Can You Do To Stop Your Car From Overheating?

There are plenty of steps you can take to minimize or outright prevent your car from overheating.

There are plenty of steps you can take to minimize or outright prevent your car from overheating. Here’s a list of some of the things you can do to keep your car nice and cool:

  • Install tinted windows in your car to reflect or absorb the heat.
  • Use window shades to ward off heat.
  • Regularly check your vehicle’s coolant levels
  • Get your radiator flushed by a professional
  • Refill or replace the engine coolant
  • Avoid overusing your car’s AC on extremely hot days

Frequently Asked Questions

What Does It Mean When the Car Overheats When the AC Is On and Idle?

If your car still overheats while you’re idling and the AC is on, there’s a good chance there’s something wrong with the components of your engine. For example, it’s possible the engine cooling fan is broken, or the fan switch, fan clutch, and fan motors are malfunctioning.

Another potential cause behind this particular problem is the water pump being damaged. Blocked AC condenser fins  and clogged radiator fins are also known to contribute to overheating issues in your vehicle, so be sure to inspect your engine.

Can I Still Drive A Car That Overheats When Idling?

Under no circumstances are you to drive your vehicle while it overheats. Driving a vehicle with an engine that’s strained and overheating will damage it, leading to costly repairs. If your car is showing signs of overheating, it’s a good idea to pull over as soon as you’re able to.

Once your car is parked, you need to prioritize bringing it to a mechanic. You can either have your car towed or drive to a garage yourself after letting the engine cool. If you plan on doing the latter, give your car 30-40 minutes to cool down before heading out.

About The Authors
Reviewed By Anthony Harlin, ASE Certified Master Automobile Technician

Technical Reviewer at CarParts.com

Tony Harlin is a Master Gas and Diesel Diagnostic Technician with over 18 years of experience. He works full-time at a large independent automotive shop as a driveability and repair technician working on all types of vehicles with a focus on diesels. ASE certifications include A1-A9, L1 and L2, as well as X1.

Written By CarParts.com Research Team

Automotive and Tech Writers

The CarParts.com Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by CarParts.com's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

Share
Published by
CarParts.com Research Team and Anthony Harlin, ASE Certified Master Automobile Technician