(Updated on November 8, 2022)
Combustion engines generate power through many small, controlled explosions. The combustion process generates an immense amount of heat, requiring a carefully engineered cooling system to keep the engine running properly.
Without the cooling system, the engine would quickly overheat, causing permanent damage. In extreme cases, overheating can cause total engine failure. An engine failure could cost close to five figures to repair in today’s market.
That is why it is important that you catch this problem in time before it gets too bad. Furthermore, you need to understand the causes of car overheating, so you know how to fix the problem and prevent it from happening again in the future.
How Hot Is Too Hot?
Most auto experts say that damage to the mechanical components of the vehicle could occur if the engine becomes hotter than around 250°F. However, each engine and coolant mix is different. Straight water (with no antifreeze) will boil around 248°F. Using a 50/50 antifreeze mix should raise the boiling point to over 265°F.
The temperature gauge will indicate the engine is too hot. You may also see an engine warning light come on your dashboard. In extreme cases, you will see steam rising out of the engine. Steam indicates that your coolant is boiling and is no longer capable of cooling the engine effectively.
Why Is My Car Overheating?
There are many reasons your car could overheat, so you will need to do some troubleshooting or diagnostic work to find the root cause. Here are some common causes of overheating.
1) Coolant Leaking
One of the main causes of car overheating is when the coolant is leaking from the hoses of the cooling system. These hoses are responsible for transferring the coolant fluid from the cooling system to the engine.
If these hoses get damaged or worn out, any tiny hole in them will cause coolant to leak out. Then there wouldn’t be enough coolant circulating through the engine, which would cause overheating after a short while.
To get yourself to the nearest auto shop right away, you’ll have to refill your cooling system with enough coolant so you can get there without overheating. This may require stopping to check the coolant several times. Remember to never open a pressurized cooling system while the engine is hot!
Following a coolant leak, more air will build up inside of the cooling system than coolant fluid. All this accumulating air forms a large air bubble known as an airlock.
This airlock prevents the remaining coolant from circulating through the engine any further, which results in the engine becoming even more overheated. That is a big reason why you need to take care of the coolant leak before it gets to the point when there’s an airlock.
3) Low Antifreeze Concentration
If you live in a northern location where there are cold temperatures and it becomes below freezing outside, gel could form inside of the coolant while it sits in the engine. This may happen if there is too low of a concentration of antifreeze for the amount of water in the coolant mixture. The rule of thumb is a 50/50 mix between antifreeze and water.
Gel in the cooling system will create a blockage that prevents the coolant from circulating in and out of the engine. As a result, the engine could begin to overheat.
4) Bad Water Pump
Another common cause of car overheating is when the water pump goes bad. The water pump is the primary component which allows coolant to circulate through the engine and cool down its components.
Unfortunately, the water pump can wear down and then eventually break once its impeller stops working. It won’t be too much longer after that until the engine begins to overheat and cause much bigger problems for the vehicle.
5) Bad Thermostat
The cooling system of every vehicle has a thermostat which regulates how much coolant is allowed into the engine. If the engine is cold, then the thermostat will keep the chamber closed so that no coolant can enter the engine.
When you turn on the engine, the thermostat starts closed because the engine is designed to run at a specific operating temperature. Normal operating temperature is somewhere between 190 and 220°F (approximately 100°C). The engine runs best when it reaches this temperature as quickly as possible.
Once the engine temperature reaches a certain threshold temperature, the thermostat opens the cooling system so colder coolant from the radiator can flow to the engine. The thermostat will usually open once the engine is at around 200°F. If the thermostat is stuck closed, your engine may overheat because there is no way for the radiator to cool the engine.
6) Heat Soak
Heat soak is what happens when a cooling system is building heat faster than it can dissipate it. This may happen in very hot climates while running the A/C, or under constant high loads. Your engine is under constant high loads when you climb a steep mountain pass or run your car on a race track.
If your cooling system is not designed for the sustained loads in those conditions, you will see your temperature start to rise. If your cooling system is functioning normally, you will see temperatures drop almost immediately once you back off the gas for a little while.
7) Bad Intake Manifold Gasket or Head Gasket
If you suspect you may have a bad head gasket, you can check by doing a leak down test. A leak down test blows compressed air into each spark plug hole and where this air comes out can quickly help you determine the general health of your engine.
An air leak in the cooling system is a strong indicator of a blown head gasket.
8) Bad Radiator Fan
If you’re moving slowly for a while and your car starts to overheat, check your cooling fans. Radiator fans are designed to pull air through the engine when the vehicle is not moving fast enough to do so.
If your radiator fans aren’t working, your car should cool down fairly quickly once you start moving again.
9) Cracked Head or Block
Although rare, it is possible for the engine itself to develop a crack in the top end (cylinder head) or the bottom end (block) of the engine. A cracked head or block is a serious engine issue and requires replacement of the cracked part(s).
This type of issue is pretty rare, and typically only happens when an engine has overheated excessively many times.
What To Do if Your Engine Overheats
If your engine starts to overheat, here are some easy steps that can help keep your engine cool.
1) Turn Off Your A/C
Your air conditioning system builds heat, and the hot air from the condenser often blows right through the radiator. This means your radiator receives mostly hot air to cool down the engine.
If your vehicle is equipped with a front mount intercooler, that’s another component that is going to heat up the air before it reaches the radiator. Keep this in mind if you are researching aftermarket upgrades for a turbocharged engine.
2) Turn On Your Heat
Your heater core is basically a small, secondary radiator. If your main radiator can’t keep up, consider blowing the engine heat through the cabin on full blast.
3) Short Shift
Short shifting keeps the RPM lower. High engine speeds generate more heat than low engine speeds.
4) Check Your Radiator Airflow
If you have an older car, check to make sure there’s no debris blocking airflow to the radiator. Check between the condenser and radiator as well.
Radiator fins are made out of thin aluminum and are easily bent upon impact. Over time, many bent radiator fins will affect cooling ability. Although the process is quite tedious, it is possible to unbend these radiator fins one by one. Some people opt to replace the radiator instead.
5) Upgrade the Radiator
As a last resort, you can try upgrading to a bigger radiator. Sometimes you just need more cooling capacity, and a larger aftermarket radiator can be a great way to handle that.
Consider this option if you’ve tried all the others, and regularly see heat soak due to high ambient temperatures.
What NOT to Do
1) Don’t Ignore It
If your car starts to overheat, you need to address the issue as soon as possible. If you are driving fast, try easing off of the throttle. If temps continue to rise, bring the car to a stop and idle for a while, letting the radiator fans cool the engine under very low load.
If the temperature continues to rise after taking these steps, shut down the engine and wait for the car to cool completely.
2) Don’t Keep Driving
If your car overheats, you need to figure out the root cause and address the issue. Don’t let the car continue overheating multiple times. Continuous overheating leads to much more expensive issues.
For instance, a $10 thermostat could turn into a $6,000 engine replacement if you crack the block from the increased pressure.
3) Don’t Panic
It’s normal to be a little alarmed when you see the temperature gauge pegged toward the hot side. Try not to worry, and don’t make any abrupt maneuvers that could cause an accident.
In most cases, if you catch this early you can prevent any real engine damage. Pull over only when you know it is safe to do so; it’s better to keep driving with a hot engine than to stop in the middle of the freeway.
How Long Does It Take for an Engine to Cool Down?
Engines take a while to cool down. The time varies based on ambient temperature and how hot the engine got when it overheated.
If you only need to bring the temperature back to normal operating temperature, you may be able to get away with waiting for only 30 minutes. However, it generally takes about 3-5 hours for an engine to cool completely down to the ambient temperature.