Here, you will find useful basics and important tips on the topic of intercooling in vehicles.


Exhaust turbocharger do provide the cylinder with more combustion air. But the air gets heated during combustion and that has disadvantages. Today, all charged engines are therefore equipped with intercooling. Discover on this page the operating principle of this system and what technical tricks development engineers use for meeting current and future requirements in the area of intercooling. You will also find practical tips here for replacing an intercooler.

Important safety information
The following technical information and practical tips have been compiled by HELLA in order to provide professional support to vehicle workshops in their day-to-day work. The information provided on this website is intended for use by suitably qualified personnel only.



The trends towards increasing engine performance and downsizing lead to an ever greater share of turbo-charged engines for passenger cars. Today, engines are generally charged with cooled air. The higher charge air density achieved by this increases performance and efficiency of the engine. However, not just the share of turbo-charged engines is increasing but - due to the continuous requirements for reduced consumption and emissions - also the requirements for intercooling capacities. This may be provided by cooling the charge air with a coolant instead of cooling with air. 


Because of the system costs, that technology was previously used only in the higher-priced passenger car segment. New developments also enable regulation of the intercooling. This means that HC emissions can be reduced in addition to the reduction of the NOx emissions and the efficiency of the exhaust gas final treatment can be improved. 


In addition to improved cooling capacity, another demand is made on intercooling: temperature control of the engine process air via intercooling control. 


The temperature regulation becomes necessary due to the constantly increasing requirements on exhaust gas final treatment. There, the temperature of the charge air plays an important part. Thus, the cooling of the charge air with coolant offers decisive advantages even in commercial vehicles.


Air cooled and coolant cooled. Direct and indirect.


Increased engine output through increasing charge air density (more combustion air, greater oxygen share).



  • Increased dynamic cooling capacity
  • Improved engine efficiency due to increase in charge air density
  • Reduced combustion temperature leading to improved emission values
  • Fewer nitrogen oxides between -40 °C and 160 °C
  • Test pressure = 20 bar with a bursting pressure of 50 bar


The power output of a combustion engine depends on the amount of fuel burnt. Required for gasoline engines: 1 kg fuel, 14.7 kg air for complete combustion. This is the so-called stochiometric ratio. Therefore, an efficient way to increase the power output is the turbo-charging of combustion engines.

Exhaust turbocharging

Replacing intercooler following turbocharger damage

Replacing intercooler following turbocharger damage


00:57 min


In passenger cars, the increasing demand for cooling capacity meets the increasing restrictions with regard to installation space in the engine compartment. Today, compact charge air coolers are still dominant. A solution to the problem of shallow installation depth consists in enlarging the compact intercooler to a flat radiator installed in front of the coolant radiator, as is standard in heavy commercial vehicles. Accordingly, this type of construction is increasingly used. However, this is not possible in many vehicles because the installation space needed is already assigned or not available due to other requirements such as pedestrian protection. With two new systems, the conflict between installation space and performance requirements can be solved: direct and indirect intercooling.

Direct intercooling

Thanks to the use of the new charge air preliminary radiator supplied with coolant from the engine circuit, a part of the charge air waste heat is shifted from the intercooler to the coolant radiator. In this way, the additional intercooler waste heat generated as a consequence of the performance increase is dissipated through the preliminary radiator and the concept of a block-type charge air radiator can be preserved. The charge air preliminary radiator - also a compact radiator - is to be installed between turbocharger and charge air/air radiator. Charge air preliminary cooling can considerably increase the performance of an existing concept. The space required for a charge air/coolant radiator is around 40 – 60% of that for a charge air/air radiator.

The second possibility for solving the conflict between installation space and performance requirements consists in indirect intercooling.

Indirect intercooling

In passenger cars, this cooling system usually comprises a complete coolant circuit, which is independent of the engine cooling circuit. A low-temperature coolant radiator and a intercooler / coolant radiator are integrated in this circuit. The waste charge air heat is first transferred to the coolant and then channeled through a low-temperature coolant radiator and out into the ambient air. This radiator is located at the front end of the car where the charge air/air radiator is located in the case of conventional air-cooled charge air cooling.

Since the low-temperature radiator requires considerably less space than a comparable charge air/air radiator, space becomes available at the front end. Additionally, the voluminous charge air pipes from the vehicle front end to the engine are not needed. Overall, the packaging in the front end is considerably simplified, which accordingly improves the cooling air flow through the engine compartment.


The following positive effects are provided by indirect intercooling compared to charge air preliminary cooling (direct):

  • Considerably reduced charge air pressure drop
  • Improved engine dynamics due to lower charge air volume
  • Increased dynamic cooling capacity
  • Improved engine efficiency due to increase in charge air density


After a cold start and also at extremely low outside temperatures while driving, it is reasonable to stop intercooling. Engine and catalyst thus reach their optimal operating temperature faster, thus reducing cold start emissions, mainly hydrocarbons (HC). In the case of a charge air/air radiator, this is only possible with much effort by means of a by-pass at the charge air end. In the case of indirect intercooling, however, a simple regulation of the coolant volume flow not only allows stopping the cooling of the charge air, but also regulating its temperature. By linking the coolant circuit for the intercooling with that for the engine cooling and an intelligent regulation of the coolant throughputs, the indirect intercooling can be extended into a charge air temperature regulation. The charge air can be circulated either by the hot coolant of the engine circuit or by the cold coolant of the low-temperature circuit.


Regulation of the charge air temperature is important for exhaust gas final treatment by particle filters and catalytic converters. Both require a certain minimum exhaust gas temperature for optimal operation. For the catalytic converter, that temperature is identical with its light-off temperature, for the particle filter, the temperature is the regeneration temperature necessary for the combustion of the embedded soot. In partial load operation of the vehicle (city, stop and go), these exhaust gas temperatures are not always reached. In such cases, too, emissions can be reduced by stopping the cooling or even heating the charge air, as the exhaust gas temperature is increased by those measures at any rate. Both options can most easily be realized by indirect intercooling.


Replacing intercooler

Replacing intercooler, incl. dismantling and installation.


01:27 min


Performance comparison of new concepts

The achievable performance advantage of the new concepts charge air pre-cooling and indirect intercooling shows, when comparing with today's predominant compact intercoolers and the more performative flat intercoolers:

  • Intercooling significantly improves;
  • for indirect intercooling, the charge air pressure drop is also significantly reduced.

Intercooler for greater strength requirements

Increasing loads for intercoolers regarding pressures and temperatures require a new design and new materials for radiator matrix and air closets. In passenger cars today, charge air has a temperature of 150 degrees Celsius and a pressure of 2.2 bar when entering the radiator. In the future, temperatures and pressures will increase to approx. 200 degrees Celsius and up to 3 bar. For meeting these requirements, air closets will be manufactured from heat-resistant plastic. Or the intercooler including air closets will be made entirely from aluminum.


Even higher loads are expected for commercial vehicles. Compared to 200 degrees Celsius and 3 bar, 260 degrees Celsius and 4 bar are expected due to the lower EURO-5 emission threshold values. By changing the intercooler design, the entire voltage level based on the pressure load will be lowered until the greater loads can be absorbed without a problem. Additional potential for strength increases is provided by the coolant intercooler via its compact design.