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Intercooler Basics

What is an intercooler and how does it function?

An intercooler is the heat exchanger that cools the air/intake charge on turbocharged vehicles before the air enters the inlet manifold. When the intake charge is compressed by the turbo, it heats up. When this compressed, heated air passes through the intercooler, the heat is transferred via the tubes and fins of the intercooler into the passing ambient air.

Once the intake charge exits the intercooler, it is both cooler and denser.  This leads to increased power and improved volumetric efficiency from the motor. The colder intake charge reduces the risk of harmful detonation/knock in the motor.

As fuel prices continue to rise, consumers are looking for vehicles that are more fuel-efficient.  At the same time, they don’t want to sacrifice vehicle performance. Many vehicle manufacturers are turning to forced induction to satisfy these changing needs.  These days almost all vehicle brands offer at least one model of vehicle that uses turbocharging and almost all modern diesel engines are turbocharged too.

Using a turbocharged motor allows manufacturers a good compromise: the motors can be made smaller, using less fuel, but will still be capable of producing the power and performance of older and larger capacity, naturally aspirated engines. A further benefit of using a turbocharged motor is that the driver won’t feel the loss of power when using the car at altitude. For example, the vehicle will not feel drastically less powerful in Johannesburg than it will at sea-level in Durban.

On production vehicles, the most commonly used intercooler is the air-to-air intercooler. This is usually mounted at the front of the vehicle just inside the front bumper, or occasionally on top of the motor, underneath a bonnet scoop. This positioning is necessary because this intercooler relies on ambient air flowing through its core to cool intake temperatures.

The Air-To-Air Intercooler

An air-to-air intercooler has an efficient design. Most OEM and after-market intercoolers have an aluminium tube-and-fin core, with plastic end tanks that are crimped in place onto the core. Performance vehicles will sometimes use a bar-and-plate core with aluminium end tanks for increased performance and to withstand higher boost pressures.

The Liquid-To-Air Intercooler

Less frequently used is the liquid-to-air intercooler, sometimes referred to as a charge cooler. These are far more complex to manufacture and install, but due to their efficiency and design, they can be mounted anywhere in the engine bay, not tucked into the front bumper.

The heat of the intake charge is not transferred into passing ambient air, but rather into the vehicle’s coolant. The air and coolant do not make contact as they pass through different channels in the charge cooler. The coolant is pumped through channels around the tubes that carry the intake air.

Apart from the complexity of manufacturing a charge cooler, it requires extra coolant lines – in some cases an auxiliary coolant pump and an additional radiator.

Failure of the Intercooler

There are some common faults that may require replacement of your vehicle’s intercooler:

  • Inefficient cooling:
    • either the inside of the cooler becomes soiled over time (usually caused by oil vapours from a leaky turbo seal or excessive crank-case breathing), or
    • the outside becomes clogged with grass and road grime beyond the point of being cleaned, or
  • Small leaks from stone chips
  • After damage from an accident

If the cooler is blocked up (either by debris outside or excessive oil inside) it will operate less efficiently.  In the long run, this will cause higher fuel consumption, a loss of performance and possible engine damage.

If an intercooler has a leak it should be replaced as soon as possible. Driving the vehicle with a boost leak will result in turbo wear, or failure, as the turbo has to work increasingly harder to achieve the desired boost pressures.  This can result in the turbo’s maximum safe RPM being exceeded.

If a vehicle’s turbocharger has suffered severe mechanical failure, the intercooler should also be replaced. The compressor wheel of a turbo can spin at up to 150,000 RPM. Usually, this wheel shatters when the turbo fails and sends shards of steel or aluminium through the boost piping of the vehicle. These shards usually gather somewhere within the intercooler.

In some cases, a specialist workshop could attempt to clean the intercooler, but the cost of this cleaning usually isn’t much cheaper than replacing the intercooler with a quality aftermarket part.

There is also no guarantee that all the metals shards will be removed by the cleaning. If a shard is left behind after cleaning, it can later become dislodged and will continue its path through the boost pipes of the vehicle. If the shard enters the turbo, this can result in another turbo failure.

This could possibly cause major engine damage if the shard of metal lodges itself on the piston face or between a valve, and a valve seat. It should also be noted that due to the internal design of the tubes on some intercoolers (those with turbulator fins for example) cleaning is simply not possible.

The Intercooler and Vehicle Modifications

The capabilities of the intercooler should be taken into consideration when modifying the performance of your vehicle. Increasing an engine’s power is no longer the dark science known only to a few. Modern technology makes it all too easy to change the software on a vehicle’s ECU to increase turbo boost pressures and adjust fuelling and timing to match.

Most factory-turbo vehicles will be fitted with aluminium and a plastic intercooler and these can only handle a certain amount of boost pressure. If one modifies a vehicle to produce higher boost pressure than what the intercooler can handle, it will cause the plastic end tanks to be blown off the intercooler.

This cannot be repaired and could cause consequential damage. It would be a smarter choice to limit modifications to a reasonable level or to consider upgrading the intercooler to suit: by fitting one from a similar, higher performance model or by using a custom-built intercooler made entirely of aluminium.

In conclusion, turbocharged and intercooler vehicles are becoming increasingly common on our roads. There is a chance that you will own one such vehicle at some point. It could be anything from a small, one-litre sub-compact, to a fire-breathing top-of-the-food-chain, performance sedan. Some knowledge of the intercooler can go a long way.

Hopefully, the above has helped you to have a better understanding of both the function and the importance of something as seemingly simple as the intercooler. Your vehicle is likely to be one of your most expensive assets.  This knowledge could save you money in the long run, not only in simple, daily fuel savings achieved by a happy, healthy car but also by avoiding costly and unforeseen engine repairs.

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