An overheated engine is a massive problem for any driver, but if your engine is heating up while your car is idle is even more dangerous. If you have this problem it is important to know why this is occurring and how to fix this issue as quickly as possible.
Some common reasons a car will overheat while idling are:
- Not enough coolant
- A broken engine fan
- And cracked vacuum hoses
There are also many solutions to a car that overheats while idling, such as:
- Topping off your fluids
- Fixing your fan system
- And inspecting your engine
Regardless of why your engine is overheating and how you fix it, you should address the issue as quickly and thoroughly as possible.
This article will go into more depth about what common problems cause a car to overheat while idling and how to fix them.
Why Your Car Overheats When Idling and Solutions
If you have a problem with your engine overheating while it’s idle, it is important to identify and fix this issue as soon as possible.
Common Causes of Engine Overheating
There are a number of issues that can cause your engine to overheat, most of which deal with the cooling systems. One or more of these problems is likely the cause of a vehicle overheating while idling.
An empty radiator or coolant system. Water and coolant are used to keep your engine cool while running, so if either your radiator or coolant system is empty then your engine will start to overheat. You can also have air bubbles in your coolant line, which prevents coolant from reaching the engine
A broken fan belt. If you have a manual engine fan in your vehicle, then overheating might be a sign that the belt or gears that drive the fan might be damaged. This is particularly common among older vehicles, as the wear and tear of age can cause fan blades to snap.
A broken electrical fan system. Modern vehicles also add fans to their engines to help keep cars cooler for longer, but these fans can also break down. A broken electrical fan can be caused by either physical damage, loss of power, or problems with the electrical system.
Fill your Radiator
The easiest way to fix an engine that overheats on idle is to simply top off the radiator with fresh water. However, before you do this be sure to check if there is any damage to the radiator or hoses, since this will stop an otherwise full radiator from working properly.
- Step 1: Open the radiator cap, preferably when the engine is cool and safe to touch. Be sure to give the radiator cap a partial turn so the pressure in the radiator can vent.
- Step 2: Check the level of liquid inside the radiator. There will be a level indicator inside the radiator to tell you how full it should be.
- Step 3: Top of your radiator with a mixture of water and coolant. The mix should be evenly split between water and coolant, but you made need to change the mixture depending on what is left in your radiator.
- Step 4: Put the cap back on your radiator and pump the safety lever if you have pressure cap.
Top off Coolant Levels
Beyond the radiator, most cars also have a separate coolant reservoir that helps keep the engine from overheating. This system also needs to be kept topped off with coolant to keep your engine running cool, so be sure to check both when looking under the hood.
- Step 1: Make sure your car has completely cooled off before you open the hood. Then locate the coolant reservoir, which should be connected to the radiator.
- Step 2: Check the level of coolant inside the reservoir against the level indicator inside the chamber, which tells how much fluid the reservoir can hold.
- Step 3: Mix equal parts water and coolant and pour the mixture into the reservoir until you reach the fill line. Be sure to wait and see if some coolant drains out of the reservoir before you reseal the reservoir.
- Step 4: Once the reservoir is full, put the cap back on and make sure it is closed.
Check your Fan Belt
If the belt on your engine fan is broken or damaged then it will prevent the fan from running and keeping your system cool. While damage to the fan itself can stop it from working, the fan belts are the most likely reason why your engine fan would stop and is also the easiest to fix.
- Step 1: Make sure your engine is cool before you open the hood. Wait a few hours after driving before looking at your fan belts.
- Step 2: Open the hood and locate your fan belts. These should be connected to a series of pulleys and gears on both sides of your engine block.
- Step 3: Remove the fan belts and inspect them for any signs of damage. If the belts are obviously torn or damaged then be sure to remove any pieces from the engine and floor of your car.
- Step 4: Put new fan belts into the pulley system.
Inspect your Electric Fan
Another feature attached to your radiator is an electric cooling fan which helps keep the system from overheating and wasting fluids. If this system is broken then even a full radiator and reservoir will not be able to keep your engine cool.
- Step 1: Let your engine cool before you attempt to open the hood and inspect your electric fan system.
- Step 2: Locate the electric fan on your radiator. It should appear as a black frame connected to the side of the radiator housing.
- Step 3: Check the wires connected to the fan and make sure they are not damaged. If they are they will need to be professionally repaired.
- Step 4: If the wires are intact, then you will need to reference your owner’s manual to find out where the fuse box in your car is. Locate the fuse box and replace any broken fuses in the system.
If you have an engine that overheats while you idle, look through all of these components to find out what the source of the problem might be.
How to Tell if your Thermostat is Broken
While a rapidly rising vehicle temperature is never a good sign, a high thermostat reading may not be from overheating. A broken thermostat can register extreme changes in heat, even when the actual engine temperature is fine, making it impossible to tell what your real engine temperature is. If you have any of the following signs, your thermostat is likely broken.
Rapidly rising engine temperatures. The first sign that your thermostat is not working is if the temperature in your car seems to rise rapidly whenever you start the vehicle. If you turn on your car and find the temperature has jumped 15 or more degrees without any major driving on your part, then your thermostat is likely the problem.
Erratic swings in temperature. Another key sign that your thermostat might be broken is if wild changes in temperature that have nothing to do with how you drive. Sudden spikes or dips in temperature, regardless of how fast you are going or the environment around you, are another sign of a broken thermostat.
Leaking coolant. Finally, one sign that your thermostat is in serious need of repair is coolant leaking under your car or into your dashboard. Since the thermostat controls coolant usage, a broken thermostat can become clogged, causing coolant to either leak out from under the car or into the thermostat housing itself.
How to Cool Down your Car’s Engine
If your car engine is genuinely overheating, there are some ways to help cool the engine down and prevent your engine from being damaged. In the event your car does overheat, the ideal thing to do is pull over and stop driving until it cools down, but there are some other ways to help cool an overheated engine off.
Turn off the A/C. As counter-intuitive as this sounds, the air conditioning system can put major strain on your engine and actually cause it to heat up faster. If your engine is overheating your first step should be shutting off the A/C if you have it on, and avoiding the A/C if you aren’t using it already.
Turn up your fans to heat. Again, this might not make immediate sense, but turning your fans to heat will siphon excess heat off the engine block to keep it cooler. This may not be ideal, especially in hot weather, so rolling down your windows can help keep you cool.
Put the car in neutral and rev. If you find a safe place to stop, put your car in neutral and rev the engine a few times. This combination will slow down your engine while triggering the fan and coolant systems to work harder, making your engine cool down faster.
Open the hood. If all else fails, pull over, stop your car, and open the hood to expose your engine and help it cool down much faster. It is important that you don’t touch any part of the engine or try to cool it off with water, just open your hood and let the engine air cool.
While an overheating engine is dangerous, an engine that overheats while the car is idling needs to be addressed immediately. If you have any questions about how to deal with an overheating car, comment with them below.
Hi, I am Brad. Car Independent is your source for independent views on cars and car accessories. Whether you looking to buy a new car or something cool for your car, you have many options. My aim to help you make the best-informed choices.