How an Intercooler Works | Tuning 101

An intercooler is a device used for cooling compressed intake air, commonly found alongside forced induction (turbocharged or supercharged) internal combustion engines. Both turbocharger and supercharger systems rely on compressed air to deliver a bigger boost to the engine, but compressing air also raises its temperature. That’s where an intercooler comes in as it cools the compressed air and increases its oxygen density before sending it to the engine itself. An intercooler is an essential part of any forced induction system, but not each of them is created equals. To help you find the right one for your car, here’s how intercoolers work, the most common types, and a couple of tips and tricks along the way.

How Does an Intercooler Work?

An intercooler works on the heat exchange principle. A turbocharger or supercharger compresses the air, which increases its temperature. This compressed hot air then enters an intercooler where highly thermal conductive access tubes absorb its heat and cool it down. By cooling the air, an intercooler provides more oxygen-rich air to the engine, which in turn increases the volumetric efficiency of the engine. This, in turn, allows the engine to burn fuel more efficiently and effectively, boosting the engine’s performance in the process.

ETS 04-07 Subaru STI Front Mount Intercooler 3.5 Upgrade
ETS 04-07 Subaru STI Front Mount Intercooler 3.5 Upgrade

What is an Intercooler for Turbo?

Regardless of whether we’re talking about turbocharger or supercharger systems, an intercooler has the same purpose. However, intercoolers in a turbocharger-based system is a more common option nowadays. After all, turbochargers are much more widespread than blowers. The intercooler slots between the turbocharger and the engine’s intake manifold and cools the compressed air coming out of the turbo before it enters the engine’s combustion chamber. 

Intercooler vs. Radiator

Although both the intercooler and the radiator exist for the sole purpose of cooling something down and are working on the same principle, they’re typically two completely unrelated parts, doing different tasks. As mentioned above, an intercooler exclusively cools compressed intake air coming out of the turbocharger or supercharger. A radiator, on the other hand, is there to cool down the liquid coolant circulating through the engine block.

In other words, a radiator is there to help keep the entire system within the optimal temperature range by regulating the circulating coolant. In contrast, an intercooler only cools down the compressed air before it enters the combustion chamber. Putting it in an even more straightforward way, all cars come with a radiator of their own, but only those with forced induction engines also sport an intercooler.

Different Types of Intercoolers

Classification by Coolant Type

  • Air-to-air intercooler is the most common type of intercooler. It relies on airflow through its core to lower the intake air’s temperature. Hot intake air inside the intercooler exchanges heat with cold, clean air coming from outside. Air-to-air intercoolers rely on vehicle speed above all else. Overheating might become an issue when there’s insufficient airflow (idling for more extended periods). Being the simpler of two options, air-to-air intercoolers are more affordable and less maintenance-needy than their liquid-cooled counterparts. 
  • Liquid-to-air intercooler uses engine coolant to transfer heat from the compressed intake air within it. The air and coolant are in their separate passages and don’t make direct contact, but liquid-to-air intercoolers are extremely efficient regardless. Being more efficient and complex than air-to-air intercoolers, liquid-to-air units are typically found in high-output applications, which naturally produce more heat.
Front Mount Intercooler
Front Mount Intercooler

Classification by Intercooler’s Location:

  • Front-Mount Intercooler (FMIC) that exchanges heat directly with the atmosphere is typically near the front bumper, in front of the car’s radiator. The most significant advantage of this positioning is the fact that it usually produces the lowest intake air temperatures. However, this comes at the cost of higher turbo boost lag as the compressed air takes the longer route between the turbocharger and the engine. Typical cars with FMIC are the Nissan Skyline, Mitsubishi Lancer Evolution, Dodge SRT-4, and Chevy Cobalt SS.
  • Top-Mount Intercooler (TMIC) is naturally sitting atop the engine. The “hottest” of the three setups usually draws the air from a hood scoop. It usually produced the highest intake air temperature as it’s sitting directly on the engine; however, it also comes with a lower lag. Notable examples of the TMIC setup are the Subaru WRX STI, MazdaSpeed3 and 6, and Toyota Celica GT-Four.
  • Side-Mount Intercooler (SMIC) is usually mounted in the front corner of the bumper or in front of one of the wheels. It’s considered as a compromise between the FMIC and TMIC. This setup is a rarity nowadays, although it was once used across numerous applications such as the Toyota Supra, Nissan Silvia, Mitsubishi Eclipse, and Audi TT.
Top Mount Intercooler

Classification by Core Construction

  • Tube-and-Fin intercoolers are more common on stock applications because they’re cheaper to manufacture. They typically consist of extruded tubes with fins pressed into place. Apart from being more affordable, they’re also lighter than other types. However, tube-and-fin-type intercoolers aren’t as robust as their bar-and-plate counterparts, which makes them susceptible to damage – especially if they’re front-mounted. 
  • Bar-and-Plate intercoolers are often available as aftermarket units as they’re more damage resistant, come with higher pressure tolerance and better heat transfer. They are, however, heavier and more expensive than their tube-and-fin core type counterparts. Another advantage of bar-and-plate intercoolers is their ability to soak up more heat while stationary, and then dissipate it once the vehicle is in motion. This is extremely useful in consistent stop-and-go situations.

Bad Intercooler Symptoms

Like any car part, intercoolers too can become faulty. Whether they’ve been damaged by objects thrown from the road or clogged by oil or dirt, given enough time, intercoolers will eventually exhibit a drop in cooling efficiency.

Typical signs of a faulty intercooler are:

  • A noticeable reduction in engine power
  • Increased fuel consumption
  • Air going into the combustion chamber is too hot
  • Black smoke from the exhaust system, etc.

Can You Drive With a Bad Intercooler?

Technically, a vehicle can still work even with a faulty intercooler, but, as you can imagine, that isn’t advisable. In a best-case scenario, your engine will simply lose its turbocharging benefits. Consequently, its output will significantly decrease. This might happen if the intercooler fails to cool the charged air properly. If the intercooler gets clogged and compressed air doesn’t make it to the engine’s combustion chamber, the engine will be deprived of oxygen and won’t be able to burn fuel at all. Leaking intercooler symptoms, on the other hand, will be slightly different as it may appear there’s no turbocharging whatsoever, depending on the size of the leak.

In any case, driving with a bad intercooler can potentially lead to more serious engine damage. Premature detonations within the combustion chamber won’t lead to anything good. Excess fuel will be ejected through the exhaust system and burned there (hence the black smoke), damaging the catalytic converter. At the same time, the temperature will go through the roof, potentially leading to a critical failure.

Mishimoto Gold Intercooler for Ford Focus ST 2013+
Mishimoto Gold Intercooler for Ford Focus ST 2013+

How to Replace a Bad Intercooler?

The easiest of intercooler repairs are related to leaks. In that case, simple epoxy or somewhat more serious weld patches usually do the trick. This, however, should not be a permanent solution. Also, it’s advisable to flush the intercooler of oil, carbon, and soot sludge with water before commencing repairs.

Patching up your intercooler might also work but it will eventually fail and potentially cause a much serious issue. It’s advisable to replace either the core or the entire unit. Especially since air-to-air intercoolers usually start from around $100 or under for the most affordable units, which makes them relatively cheap to replace in the first place.

Cost to Replace an Intercooler

As mentioned above, the most basic of intercoolers usually start from just under $100. Still, more complex units can command prices that are multiple times higher – especially when it comes to branded aftermarket units. That’s the reason why replacing an old intercooler with a new one can be expensive. Cleaning and repairing a faulty intercooler is naturally more affordable but might not be worth the investment — especially if it’s a cheap unit that you’re planning on replacing with another similar product.

Last Words

Intercoolers aren’t an integral part of the engine cooling system like radiators, which means that risks of running a faulty unit aren’t as high as with a defective radiator, which could potentially fry your engine within minutes. However, since they cool the compressed intake air coming out of the turbocharger or supercharger, they still play an essential role. Without the intercooler, the intake air wouldn’t be dense (oxygen-rich) enough, which would translate to poor efficiency as such air isn’t capable of burning as much fuel as the cold air. Not to mention the potential premature detonations within the combustion chamber, which would result in possible engine damage. An intercooler thus plays an important role in helping forced induction applications run at optimal efficiency and maximizing the turbocharger/supercharger gains.

About Nikola Potrebić

Nikola strives to preserve the untold stories of the '70s and '80s special-edition and limited-run models from the U.S. market. He also has a penchant for Saabs and Volvos, and wouldn't mind seeing more contemporary cars with a manual gearbox.

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