Main Causes of Car Engine Overheat & What Not to Do


In the good old days, engine overheat wasn’t such a big deal —once that temperature gauge shot up, all you had to do was pull over, let the cast-iron block and heads cool down for about an hour, add coolant and you were back on the road.

Well, things don’t work that way, anymore. With aluminum engines, a timing belt, and a bunch of sensors under the hood, a single overheating incident can be enough to result in a warped head, blown head gasket or other serious problems.

But there’s one thing that hasn’t changed over the decades. Even on new cars, the cooling system has a manageable number of parts: the radiator, hoses and hose clamps, thermostat, water pump, coolant temperature sensor and cooling fan. That’s good news because it does narrow down the number of potential problems during a diagnosis, but there are a few other things to consider –


If you’re able to take steps to cool your engine before it overheats to the point of failing, you may reduce the risk of irreversible engine damage. But first, you’ve got to notice the symptoms of overheating, which can include:

  • Steam (which can look like smoke) coming from under the car hood.
  • An engine temperature gauge on your dashboard that spikes to “H” or into the red. (Engine temperature gauge symbols vary, so consult your owner’s manual.)
  • A strange smell coming from the engine area. For example, leaking coolant can smell sweet while leaking oil might smell more burnt.

Engines can overheat for many reasons. In general, it’s because something’s wrong within the cooling system and heat can’t escape the engine compartment. The source of the issue could include a cooling system leak, faulty radiator fan, broken water pump, or clogged coolant hose.

Regardless of the problem’s source, an overheating engine isn’t something you want to let linger. Your engine could sustain serious, if not permanent, damage.

Let’s break down the main causes:

Low Coolant Level

The most common cause of overheating is a lack of coolant. The radiator and its plastic hoses are not designed to withstand high temperatures and can fail if they get too hot. Coolant is the liquid that circulates through your engine to absorb excess heat, helping the engine maintain a steady temperature. If your car overheats, it might be because your coolant level is low. Just like transmission fluid or motor oil, coolant has a service cycle and needs to be changed at recommended intervals. Otherwise, it breaks down and loses its ability to prevent boilovers or freezeups as well as losing its anti-corrosion properties. Your coolant should be bright green (or blue, purple, orange or whatever its original color was). Coolant that’s looking brownish is aged and degraded.

An empty coolant reservoir tank could be caused by a potential leak. Leaks in the coolant can often be identified by spots or puddles on the ground. Be aware that coolant will have a sweet smell and may be green, blue, or orange in color depending on the type of coolant being used.

Faulty Thermostat

Your engine needs to get to operating temperature quickly, and the thermostat prevents coolant from going through the radiator until the engine warms up. At a predetermined temperature, the thermostat should open to allow flow through the entire system. A thermostat that’s stuck shut would mean the engine will overheat quickly, as coolant doesn’t make it to the radiator to dissipate heat. Conversely, a stuck-open thermostat means that the engine might never reach operating temperature.

Broken Water-Pump

The water pump’s job is to circulate the coolant throughout the engine. If the coolant is dirty or has too much buildup, it can stop the coolant from moving through the pump, which can lead to an overheating situation.

Radiator Issues

Radiators and their fans help to reduce heat from the engine by decreasing coolant temperatures. Issues with the fans may reduce the capability of the radiator to remove heat, which will cause unnatural temperature increases.

Broken Gasket

The head gasket in your vehicle keeps the engine block and the cylinder head separate. If it blows, coolant can get into the combustion chamber and oil can get into the cooling system. Though this can cause a visible coolant leak, it can also cause lower coolant levels without a visible leak. You may also notice milky-white oil and white smoke coming from the exhaust pipe.


Here are a few signs that indicate overheating in a vehicle:

  • The temperature gauge rises above the middle mark on the gauge.
  • The coolant light comes on or flashes.
  • You hear the engine running louder than usual.
  • Steam is coming from under the hood.
  • The engine may stall during acceleration or deceleration (going up or down hills).
  • Some newer vehicles may WARN you to shut the car off now.


There are quite a few dos and don’ts when your car is overheating. Try to get the vehicle to a safe space for you, your vehicle occupants, and other drivers on the road. Until you can get to a safe space, decelerate, turn on the heat and stay calm.

Do not use your air conditioner when you are stuck in a standstill or in very slow-moving traffic in hot weather. Instead, open the windows and turn on the heat. These are prime conditions for a car to overheat. 


This might seem counter-intuitive, but when your car is overheating, don’t turn on the air conditioning or any other electrical components in your vehicle. When you do this, more electricity flows through the system and increases its temperature even more. Wait until you get somewhere safe before turning on any electrical components.


When your car overheats, stop immediately and turn off the engine. Park in a safe place where you won’t be blocking traffic. If you can’t do that, pull over as soon as possible so that other drivers don’t crash into you while they try to maneuver around your vehicle. If you must keep driving to a safe spot, decelerate to slow the overheating. 


If you notice that your car is overheating, don’t open the hood unless necessary. Opening the hood will allow heat to escape from under the hood and into the engine compartment, causing further damage to your car. If you must open it, cover it with a towel or blanket immediately.


Opening a hot radiator cap can cause an explosion because pressurized coolant will escape and spray everywhere if you do so before letting everything cool down first. Let your car cool down completely before attempting to open anything under the hood.

Now you know WHEN and WHY your car is overheating and WHAT not to do. Remember the safety steps you need to take when your car is overheating:

  • Stop driving.
  • Don’t open the radiator cap while hot.
  • Don’t try to open the hood
  • Call for help…


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