Intercooler: how does it work and why does your car need one?

If you have a car with a turbo engine, whether petrol or diesel, it will almost certainly have an intercooler. I say almost certainly because there are also cars with forced-induction engines that do not have an intercooler. In fact, in the 1980s and 90s it was even used as a marketing gimmick, and some cars “showed off” with “Turbo Intercooler” badges, just as others used “16V” or “GTI”.

What does the intercooler do?

Basically, an intercooler is a radiator used in forced-induction engines, whether turbocharged or supercharged. The intercooler’s job is to cool the air that the forced-induction system sends, compressed, to the intake.

Why is this done? Because the air, as a result of compression by the turbo, heats up considerably

, which reduces its density. In other words: if the air compressed by the forced-induction system goes straight into the intake without passing through the intercooler, it contains less oxygen than it would if its temperature were reduced. And remember, the principle of forced induction is to introduce more air than the engine could draw in naturally, so that combustion takes place with more oxygen, thus improving performance.
Types of intercooler

There are two types of intercooler: air-to-air, which use cold air moving in from outside to lower the temperature of the compressed air, and water-to-air intercoolers, in which the heat transfer system is a liquid coolant.

The advantage of the first type is that they are simpler, while the second are more efficient (water has a greater cooling capacity than air) and can be smaller.
Where is the intercooler located?

The intercooler is always located in the circuit the gases travel from the turbocharger to the intake. Engineers look for the best possible compromise so that the route the airflow takes is as short as possible, and so that the radiator is positioned in the most favourable way to receive outside air.

Its location in the engine bay depends on the type of engine (number and layout of cylinders) and the type of intercooler (air or water). Air-to-air units need to be mounted at the front to receive the greatest possible volume of outside air. Water-based units can be installed anywhere in the engine bay, but they also need to receive external airflow.

You should also know that an engine can have several intercoolers

. For example, one for each cylinder bank in V engines, or two small ones in parallel (instead of one larger one) to improve efficiency in inline engines where space is limited.
Maintenance and faults of the intercooler

An intercooler normally needs no maintenance beyond checking that there are no leaks in the piping.

A simple “silly” fault that is easy to fix is one of the hoses connected to the intercooler coming loose, usually because the clamp holding it has deteriorated. The symptoms are a sudden and clear loss of engine power and a noticeable “whistling” when accelerating. If there is no other associated problem, it is enough to reconnect the hose and fit a new clamp. The hoses themselves can also develop cracks due to ageing.

An intercooler can also lose efficiency if the radiator fins are damaged

, for example by stone impacts. If problems arise with the turbocharger, the intercooler needs to be checked, as it can become contaminated by oil leaking through damaged turbocharger seals.

Related information of interest
Tips for looking after a turbocharged car§h49§