Woman in front of an overheating car

Overheating Car: What You Need To Do

In a car engine, multiple metal parts rub against each other at high speed, creating a lot of heat. If heat production wasn’t controlled in some way, the temperature would quickly rise beyond the normal operating temperature, leading to engine seizure in a jiffy. To ensure engines stay cool and last as long as possible, car manufacturers invest large sums of money to design the most efficient cooling systems they can. Unfortunately, as soon as a component fails, the system will be quickly overwhelmed by the heat. When it happens, it’s important to react correctly to prevent extensive damages to the engine’s internal components. Since time is of the essence when an engine runs hotter than it should, here’s a quick description of why your engine might be overheating and some things you need to do to keep the repair bill as low as possible.

Common Reasons Why Your Car Might Be Overheating

The cooling system in your car is a sophisticated group of parts working in unison to prevent your engine from overheating. Your car’s system works by pressurizing a coolant and water mixture and circulating it through the engine and into the radiator using a pump. Heat is extracted from the coolant when air passes through the cooling fins of the radiator.

A car may overheat for a variety of reasons. Any of the key components in your cooling system can fail and will invariably result in your engine running above the normal threshold.

Coolant leak on a car

Coolant leaks

Cooling systems leaks are quite frequent and may lead to multiple problems. For starters, the cooling system on your car is a closed system, meaning that the level of coolant shouldn’t decrease. It can sometimes evaporate a little bit but a significant decrease often indicates a leak. If your car is leaking coolant, your engine will risk overheating once the coolant level is low enough.

Furthermore, cooling systems also need to be pressurized to work efficiently. Liquids boil at a higher temperature when pressurized and cooling systems use this property to their advantage. This allows the coolant/water mixture to reach cars’ normal operating temperature without boiling. If there a leak in the system or the radiator cap doesn’t seal correctly anymore, the coolant will most likely start to boil and won’t be able to dissipate heat and the temperature will rise uncontrollably.

And that’s not good at all…

Mechanical Problems Leading to Overheating

Various mechanical problems can also cause the cooling system to fail. The most common reason, and also the least expensive one to repair, is a faulty thermostat. With time, thermostats tend to stay stuck in the closed position, which will prevent the coolant from circulating into the engine’s water passages. A clogged radiator or heater core will also cause the same problem.

A defective water pump will also prevent the coolant from moving around. When it happens, it’s sometimes possible to see coolant coming out from under the water pump. Unfortunately, replacing a water pump is often quite costly because of the extensive work required to access it.

There are also more severe reasons for overheating. A cracked or blown head gasket will allow the coolant passage to communicate with the combustion chambers or oil passages and oil may contaminate the coolant. When they rise, pistons can also create excessive pressure in the system leading to ruptured hoses and large coolant leaks.

Overheating car

Radiator and Heater Hoses

All cars have two large hoses running from the water pump to the radiator and from the radiator to the engine. Since both are made of rubber and since rubber tends to dry out and crack with time, it’s common for these hoses to crack and leak.

There are also two smaller hoses running to the interior of your car and connecting the heater core to the rest of the system. If they start to leak, you should be able to see coolant under the right side of the dashboard.

You should also look for leaking hoses on the top of your engine near the intake manifold. Car engines typically have several small hoses that channel coolant to the intake system. These hoses become brittle over time and can start to leak.

Broken Belts and Faulty Pulleys

Your engine will have at least one belt driving the water pump. On older car models, the drive belt may also power the cooling fan, and that is why it’s sometimes called a fan belt. Just like rubber hoses, rubber belts will also dry out and break with time.

A common component that fails is the tensioner pulley. Its job is to apply a specific tension onto the drive belt. When the tensioner pulley’s bearing wears out, the pulley might seize and break the belt.

Electrical Problems Causing Overheating

Most of today’s vehicles use electric fans instead of a fan driven by the drive belt. However, on most vehicles, the cooling system is efficient enough to cool down the engine when driving under normal conditions. The cooling fan is then only used when idling for a long time or in extreme heat conditions. If your engine only overheats when it’s idling, that might be your problem.

Cooling fans have fuses that can blow up when too much electrical current passes through. This typically happens when a fan motor is about to seize or has a short-circuit. If your fan’s fuse is blown, make sure to find what caused the problem in the first place before actually replacing the fuse.

To troubleshoot and repair an electrical problem, you’ll need to get your hands on your car’s cooling system electrical diagrams. Even though such diagrams can sometimes be found on the internet, the safest bet is usually to get a digital copy of your car’s repair manual. Everyone knows that the information and data found on Google are not always accurate, to say the least. Just play it safe and get a quality repair manual instead.

Man looking at an overheating engine

Getting an Overheating Car Off the Road

If your engine is overheating, you need to stop driving as soon as possible. Your engine will without a doubt fail if you continue to drive with an overheating condition. You should immediately stop your car in a safe place before trying to figure out why it is overheating.

The first thing you should do is figure out if the problem is something you might be able to fix. Open your hood and inspect the engine bay for leaks. Can you see steam coming out from somewhere? If you have a leaking radiator hose, you may be able to make a temporary repair to get home. Duct tape can sometimes do the trick if you aren’t far away from a repair shop. If the reason your car is overheating is serious, like a blown head gasket, you will need to have your car towed.

Sometimes, you may be able to use some tricks to solve problems that cause overheating. If the small hoses on the intake manifold start to leak, for example, you may be able to use a piece of heater hose to replace the leaking one. Then, simply connect one of the heater hoses coming from the water pump to the other heater hose fitting at the intake manifold. You will not have a heater, but you’ll be able to get your car home.

It is important to remember that you should never pour cold water into a hot radiator. The difference in temperature can cause rapid thermal expansion that can crack your engine. Instead, keep the key ON to keep the fan blowing. Turn on the AC to start the second fan too. You can also cool off a hot radiator by spraying it gently with running water.

Wait until the engine is cooled, start the vehicle again and keep your eye on the temperature gauge. If the temperature starts to rise over the normal value, stop the car again and have it towed.

Temperature gauge on an overheating car

In Brief…

An overheating car is a very stressful situation. The best thing you can do is to let the engine cool off before testing it again. If the problem comes back, get the car safely somewhere you’ll be able to investigate further. Most cooling system problems are quite easy to diagnose and fix, even though some conditions may be harder to troubleshoot than others. In all cases, make sure to get your hands on your car’s repair manual and follow the manufacturer’s recommended troubleshooting procedures. When in doubt, you’re sometimes better off asking a trustworthy mechanic for advice. When dealing with a car’s cooling system, the last thing you want to is to eyeball it and half-ass a quick repair. Never forget that, fixing it right the first time is always the best way to save on car repairs.

Good luck!


About Derek F

Derek grew up in Southern California and started working on cars when he was a child. He learned from his father and grandfather how to make basic repairs and maintain cars correctly. Derek rebuilt his first engine at 15 years-old, beginning an automotive career that took him to many interesting jobs. Derek has worked as an automotive detailer, managed parts warehouses and auto parts stores, and worked as a mechanic for several years doing brake and suspension work. While pursuing a bachelor’s degree in government journalism, Derek worked for an auto museum where he started to write about cars. Today, Derek uses his expertise gained from many years of practical experience to help educate DIYers and share interesting knowledge about various types of automotive repair and service. Writing about cars helps fund his numerous classic car restoration and customization projects.

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