We’ve all seen those poor people stranded on the side of the road, steam billowing from the engine. Often times, an overheating engine can cause serious problems to the rest of your vehicle if not addressed immediately. But why do engines overheat? In this blog we’re going to look into what causes an overheating engine and what to do if it happens to you. But first, let’s take a brief look at the cooling system.

What Does the Cooling System Do?

Engines produce less pollutants and function best when allowed to burn fuel at high temperatures. Left unchecked, however, temperatures within the engine can continue to climb as more and more fuel is burned. This is bad for obvious reasons; when things overheat, engine parts can get damage, shortening the lifespan of the engine and putting you in danger in that process. The job of your car’s cooling system is to keep that from happening. This system allows your engine to burn fuel at the optimal temperature without letting it get too hot, keeping engine components and you safe while still maximizing performance.

The cooling system is comprised of the radiator, water pump, fan, thermostat, hoses, overflow tank and a pressure cap. The cooling process begins when the pump sends coolant into the engine. Once there, the coolant absorbs the heat from the engine, then exits to the thermostat. The thermostat gauges whether the fluid is above or below the heat threshold.
If above, the thermostat opens a valve for the fluid to flow to the radiator, where it is cooled before being recycled into the system. If below, the valve remains closed, and the fluid is recirculated back into the pump to the engine.

What Causes An Overheating Engine

Now that you understand how the temperature in liquid-cooled engine is maintained, you can have a better understanding of how that system can fail. Here are 4 common causes of an overheating engine:

Low Coolant

One of the most common cause of an overheating engine is low coolant. Just like how oil eventually breaks down and needs to be filled or replaced, coolant levels go down over time. If coolant levels get too low and go too long without being replenished, there isn’t any liquid for your cooling system to send through the pump to absorb the heat and maintain or cool it. At this point the engine is allowed to continue to increase temperature unchecked, leading to problems down the line.

Defective Thermostat

Another cause of an overheating engine is a defective thermostat. Let’s say you do, in fact, have enough coolant in your system to maintain normal operations. If the thermostat within the cooling system is defective, it won’t be able to accurately read the temperature of the fluid and send it to the radiator when necessary. This means that hot fluid will just continue to be recycled through the engine over and over, without the chance to cool the engine even when necessary. This type of malfunction can also lead to an overheating engine.

Defective Fan

Your engine cooling fan engages when necessary to help maintain the temperature of the engine. If your fan goes out, your cooling system could be compromised. Most commonly, cooling fan failure is electrical, the cause being blown fuel which can easily be replaced.

Malfunctioning Pump

Whether it’s a clog or intake issues, if your cool system’s pump is malfunctioning, you’re going to have issues with cooling your engine. In some cases this could be caused by a leak, while in others it may be a clog or a completely faulty component.

How to Tell your Vehicle is Overheating

If your engine is overheating, you’ll know. Whatever the issue is, it is always unsafe to drive an overheating car. There are several indicators of an overheating engine:

You’re in the red. On your dashboard next to your speed gauge, there’s a temperature gauge that shows the internal temperature of your car. If you’ve driven your car for any length of time, you should be failure with where that gauge typically tips (in most cases, needles hover in the lower to medium area). If you’re driving an notice that the temperature gauge need is nearing the red zone (or worse, it solidly at the edge of the dial) then you’ll know you have a problem.
Sweet smells coming from the vents. Coolant is known for having a very distinct sweet smell. If there’s a leak in your cooling system, you’ll probably know if you begin to smell a sweet odor coming from the vents.
Malfunctioning heating system. If you notice that hot air is blowing through the vents, even when on the coldest setting, there’s probably an issue with your engine and cooling system. Your heating system collects and utilizes heat from the engine. If your engine is overheating, excess heat may try to escape via the vents.


Example of coolant indicator light.

Dashboard warning light. Another sign of an overheating engine is the coolant warning light popping up on the dashboard. The indicator light is typically displayed as a thermometer.
– Steam. If you’re driving along and notice what looking like smoke billowing out of the front of your car, this can also be an issue with an overheating engine.

What To Do


If you notice any of these signs, pull over immediately. It is unsafe to drive with an overheating engine, as continuing to do so could do further damage and put you in danger in the process. If you notice that steam is coming out of the front, do not open the hood until the car has been turned off and the engine has had time to cool down.
Popping the hood prematurely could result in a face full of hot steam, which can burn you (and is just generally unpleasant). Wait a minimum of 15 minutes before attempting to open the hood.

At Beetlesmith we suggest always having a bit of coolant on hand in case of an emergency. If you have some, we suggest filling up on coolant and testing your car to see if this helps. Coolant can be added by locating the radiator cap and filling until “full” (indicated by a line). Turn the cap a quarter of the way and let pressure release before removing the cap fully.

After the cap has been replaced, turn the engine on. If the light has gone off and the temperature gauge has stabilizes, you are safe to drive immediately to the nearest service station (often this method is only a temporary fix for a deeper issue).
However, if issues persists, it’s best to call a tow truck to keep from causing further damage to the vehicle.


At Beetlesmith’s Valley Auto Service in Renton we offer cooling system checks and engine repair to help get you back on the road safely. If you’re experiencing an overheating engine, give our team a call at (425) 251- 8787.

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