One of the scariest things that can happen while you’re driving is for your engine to seriously overheat. Gauges and lights on your dashboard blink while steam can pour out from under your hood. As you frantically pull your car over and shut off your engine, you worry about whether this overheating is going to lead to major, costly repairs. 

This is the worst case scenario when it comes to your vehicle overheating, but any time your engine’s temperature is rising higher than normal, it indicates that you’ve got some kind of engine cooling system issue. Ignoring an overheating issue is a big mistake, as overheating places tremendous stress on your engine. Left alone for too long, overheating can be the cause of significant damage or may even necessitate a full engine replacement. As you can probably guess, none of that is cheap. 

Engine overheating can stem from a number of potential issues, some of which are easy to solve and others requiring a bit more maintenance work. The following is an overview of some of the reasons your car’s engine may be overheating and common fixes for those problems.

Engine Heat and Cooling System Basics

As you probably know, the engine generates tremendous heat as it works. If you’ve ever popped the hood and made the mistake of touching a part of the engine after driving it for a while, you know that even a properly cooled engine is significantly too hot to touch. 

Most vehicles will operate somewhere in the range of 195 degrees to 220 degrees. In almost all vehicles, even today’s modern vehicles, the engine temperature gauge won’t tell you an exact temperature, but will simply show a spectrum from low to high. 

Depending on the vehicle, the ‘normal’ level of engine heat may vary anywhere from midway up the gauge to below the midpoint. Anything within that range is fine. What you’ll want to do is get accustomed to your vehicle’s baseline for engine temperature, as indicated on the gauge. If you know where your engine generally tends to run in terms of temperature level, you’ll be able to notice when something changes. This can help you recognize a problem early, before you encounter any serious problems. 

Some older cars don’t have a temperature gauge at all, instead having a light that is blue when the engine temperature is in the normal range and turns yellow or red when the engine is above a certain temperature threshold. With vehicles like these, you’ll want to take immediate action if the yellow or red light comes on. 

Engine Coolant System

In order to understand some of the most common causes of engine overheating, it’s good to get a sense for the basics of how an engine is cooled. Most modern automobiles use a liquid cooling system to reduce heat as the engine runs and heats up. In a liquid cooling system, coolant (generally a mixture of water and anti-freeze) is circulated through the engine to absorb heat, and then channeled to the radiator to vent that heat. 

In order for the radiator to dissipate heat efficiently, a radiator fan cycles to ensure that there’s enough airflow to keep the radiator functioning properly. A water pump is responsible for keeping the coolant moving from the radiator to the engine and back again in a cyclical process. 

The three most significant pieces of the cooling system are the radiator (and its fan); the hoses that transport the coolant through the engine and radiator; and the water pump responsible for keeping the coolant moving. If any of those components malfunction or encounter failure, this can result in a poorly performing or failed engine cooling system, which in turn will lead to your engine overheating. 

Leaking Cooling System

One of the more common problems leading to an engine overheating is a leak within the coolant system. A leak can occur at nearly any point in the cooling system chain of components – radiator, head gasket, water pump, the hoses, or even the thermostat housing. 

If there’s a leak in your vehicle’s cooling system, this allows air to enter the system. It’s a misconception that a leak in the cooling system causes your car to overheat because significant amounts of coolant leak out. The more common problem is that air enters the cooling system and eventually forms a bubble of air known as ‘airlock’. 

If an airlock forms, the cooling system isn’t capable of circulating the coolant, which traps any coolant currently in the engine within it. That coolant becomes superheated, and the engine can rapidly overheat. 

Diagnosing a leak in the cooling system is usually fairly easy. You can lay some cardboard or newspaper beneath your engine and check back again the next day to see if any coolant (usually green, red, or orange in color) has leaked out. Similarly, lifting the hood and inspecting the radiator and engine for coolant can alert you to a coolant leak. 

If your vehicle has a coolant leak, the fix depends very much on where the leak comes from. At the lower end of the spectrum is a leak in the radiator hoses. Fixing or replacing these is fairly inexpensive, often only $40 to $60. Replacing a radiator, on the other hand, can typically run into the $300 to $400 range, and a leaking cylinder head gasket can cost several hundred dollars to replace. 

As with many automotive issues, the sooner you can have a mechanic address them, the greater the likelihood that the fix is minor and less costly to perform. 

Blocked Coolant Hoses and Contaminated Coolant

Coolant hoses can sometimes become choked with sediment and dirt from the breakdown and erosion of coolant or metallic cooling system components. When this happens, it impedes the flow of coolant, which decreases the overall efficiency of your engine cooling system. If the build-up of grime and dirt becomes too significant, it can lead to the engine overheating because the coolant can’t move through the hoses. 

Similarly, that grime permeating into your coolant system dilutes and adulterates the coolant itself. Flecks of rust, dirt and other road or plastic based particles can accrue in the coolant, causing it to be less efficient at absorbing and channeling engine heat. 

If either of these happens, the solution is to have your coolant flushed. This is a process by which our Certified Automotive Expert drains your coolant, uses a series of flushes with coolant cleaner and water to cleanse the system of any residual coolant and foreign particles, and then fills the system up with brand new coolant. 

We recommend a coolant flush every 40,000 to 50,000 miles regardless of any other circumstances. But if you’re experiencing engine overheating issues, it may be time to get your coolant flushed. 

It’s also a good idea to replace the thermostat, as preventative maintenance, during the process of flushing the cooling system, so as to rest assured it won’t malfunction (fail to open and close properly) due to debris.

Radiator Issues

The radiator is responsible for venting engine heat into the atmosphere through the coolant in the system. In order for the radiator to function properly, a number of conditions must exist. 

First, the radiator needs to be free from leaking or clogging. We discussed the possibility of a coolant leak earlier, and similar to a clogged hose, the radiator can develop an obstruction, which doesn’t allow coolant to efficiently pass into and out of the radiator. 

Second, the radiator fan needs to keep a steady supply of air circulating over the radiator, or there needs to be sufficient air flow through the radiation while driving. If the radiator is starved for air, it can’t effectively do its job of dissipating heat into the atmosphere, meaning that the entire engine cooling system will retain more heat. Eventually, that excessive heat backs up into the engine, causing overheating. One of the biggest signs that there’s a problem with the radiator fan is that a car has no problems driving on the highway or at higher speeds, but overheats at idle or in bumper-to-bumper traffic, when the fan is supposed to kick in. 

Third, the thermostat needs to be functioning properly. Technically, the thermostat isn’t a part of the radiator, but it works directly with the radiator. The thermostat controls the amount of coolant entering and leaving the radiator. If the thermostat becomes stuck or is malfunctioning, this will cause the radiator to function poorly or not at all. Usually, a thermostat will tend to either get stuck in an open or closed position. If it’s open, this will lead to a different set of problems, but a thermostat that’s stuck closed will lead to engine overheating. 

In the case of a radiator-based coolant leak in a metal radiator, the solution can sometimes be a patch to the leaking part of the radiator. However, this is often a tricky procedure, and in most instances the radiator will need to be replaced. Clogging in the radiator or anywhere in the cooling system can often be solved by a coolant flush. 

When there’s a problem in the fan, sometimes it might be as simple as having the fan cleaned. If a fan is dirty enough, this can cause it to perform poorly and lead to decreased radiator performance. Beyond that, when the fan isn’t working, there’s either an electrical problem somewhere in the fan’s electrical circuit or a failure of the fan, requiring replacement of the fan itself. 

If the problem is a stuck or malfunctioning thermostat, it’s best to just replace the thermostat. Thermostats are inexpensive enough to not bother with attempts to fix a bad thermostat.

A Faulty Water Pump

The water pump is responsible for propelling coolant throughout the entire cooling system. Anything that reduces the function of the water pump will result in poor coolant circulation, which in tern will lead to engine overheating. 

Most of the signs of a problem with the water pump are similar to symptoms of previously discussed problems – engine overheating, steam and coolant leaks. In addition to those, sometimes a failing water pump will produce a high-pitched whining noise at the front of your engine. This whining can mean that the bearings within your water pump are on the verge of failing. If you hear this noise, it’s crucial that you bring your vehicle in for service as soon as possible. Once the water pump’s bearings are worn out, you’ll need to have the water pump replaced. 

If the issue is a leaking water pump, here too, the pump will have to be replaced. 

In the case of any of these issues, the best thing you can possibly do as a vehicle owner is stay vigilant and address any problems as soon as possible. The engine coolant system is a high-pressure, high-heat system, under tremendous stress as it works through the massive amounts of heat the engine creates. This means that a little problem can very quickly become a big problem. 

It might mean noticing that little bit of coolant on the street, driveway, or garage floor; or observing that the temperature gauge is running a little higher than it normally does. These can be the signs of something not quite right with your engine coolant system. And the sooner you address the problem, the less likely you are to be stuck on the side of the road with a critically overheated engine, dreading a big repair bill.