The Smart Roadster Brabus chargecooler is one of the most significant engineering differences between the standard 60kW Roadster and the full 74kW Brabus model. Often misunderstood or overlooked in buying discussions, this compact but clever system is a core reason the Brabus can sustain 1.43 bar of boost without cooking itself. If you are trying to understand what makes the Brabus tick, thinking about upgrading a standard car, or diagnosing a power-loss issue on an existing Brabus, this guide covers the chargecooler in depth — how it is built, how it functions, where it sits in the car, and what tends to go wrong with it over time.
What Is a Chargecooler and Why Does the Brabus Need One?
A chargecooler — also known as an intercooler — reduces the temperature of compressed air leaving the turbocharger before it enters the engine’s intake. When the Garrett 1238S turbocharger compresses the intake charge, the air heats up significantly due to the thermodynamic work involved. Hot air is less dense, which means fewer oxygen molecules per unit volume, which directly reduces the mass of air the engine can combust — and therefore limits power output. It also raises the risk of knock (pre-detonation), which on a small engine like the 698cc three-cylinder can cause serious damage.
The standard 60kW Roadster runs 1.09 bar of boost and manages without a chargecooler, relying on relatively conservative tune parameters to stay within safe charge temperatures. The Brabus, running 1.43 bar, produces charge temperatures that would cause persistent knock and power loss without active cooling of the intake air. Brabus and Smart engineers addressed this with a water-to-air chargecooler system — a more compact solution than the traditional air-to-air intercooler used in many turbocharged cars, and one well-suited to the Roadster’s tight mid-rear engine bay.
Understanding how boost pressure feeds into torque at this displacement level makes the chargecooler’s role even clearer — our article on how boost translates into torque on the 698cc engine explains the thermodynamic relationship in detail.
Water-to-Air vs Air-to-Air: Why Brabus Chose a Water Chargecooler
Most performance cars use an air-to-air intercooler: a large matrix mounted where ram air flows through it, cooling the charge air before it reaches the throttle body. This works well when there is space in the front of the car and a long enough intake tract. The Smart Roadster has neither. Its engine sits behind the seats in a mid-rear layout, the front compartment is purely luggage space, and the intake path between the turbo outlet and the throttle body is extremely short. Running a long pipe to the nose and back would introduce unacceptable lag and packaging nightmares.
A water-to-air chargecooler solves both problems. The heat exchanger core sits directly in the intake path, very close to the turbocharger outlet. Coolant circulates through the core, absorbing heat from the compressed intake air, and is then pumped to a small radiator where it rejects that heat to the atmosphere. The system is compact, responsive, and does not require ram airflow directly through the core — the coolant loop handles heat transport independently.
This design does introduce one extra system to maintain: the chargecooler has its own coolant reservoir, pump, and radiator, separate from the main engine cooling circuit. Each of these components is a potential failure point on a 20-year-old car.
The Brabus Chargecooler System: Components and Layout
The Heat Exchanger Core
The chargecooler core is a small aluminium matrix integrated into the intake plenum between the turbo compressor outlet and the throttle body. Compressed hot air passes through the air-side channels; coolant flows through the water-side passages. The two fluids never mix — heat transfers across the aluminium walls. The core is compact by necessity but effective at the flow rates the 698cc engine demands, even at full Brabus boost.
The Coolant Pump
A dedicated electric pump circulates coolant through the chargecooler circuit independently of the main engine coolant pump. This is important: even when the engine is off but still hot, the chargecooler pump can continue running briefly to prevent heat soak. The pump is typically located in the engine bay area and is a known weak point on high-mileage cars. A failed chargecooler pump means the system stops cooling the intake charge entirely, even though the rest of the engine may appear to run normally. Power will drop, and the ECU may pull timing to protect against knock.
The Chargecooler Radiator
The chargecooler coolant loop includes a small dedicated radiator, usually mounted separately from the main engine radiator. On the Roadster, space is tight and the positioning of this radiator varies slightly between production runs. It rejects the heat absorbed from the intake charge to ambient air. Blockage from debris or corrosion in this radiator will reduce chargecooler efficiency markedly, particularly in hot weather or during sustained high-load driving.
Hoses and Connections
The chargecooler circuit uses a series of small-bore coolant hoses. After two decades, these are prone to hardening, cracking, and weeping at the joins. A slow coolant leak from the chargecooler circuit does not necessarily trigger an engine temperature warning — the two coolant systems are separate — so owners may not notice until the reservoir runs dry and efficiency drops sharply. Regular inspection of hose condition and coolant level in the chargecooler reservoir is advisable maintenance on any Brabus.
How the Chargecooler Affects Performance and ECU Tuning
The chargecooler is not simply a safety device — it is an active enabler of performance. By reducing intake charge temperature, it increases air density, allowing the ECU to inject more fuel and advance ignition timing without risking knock. The Brabus ECU map (stored in the Bosch MEG 1.1, firmware 1037371568) is calibrated with the assumption that the chargecooler is functioning correctly. If the system is degraded, the real-world conditions diverge from the map’s assumptions, and you will see power fall away, particularly on back-to-back runs where heat soak accumulates.
This is also why attempting to run a Brabus-level remap on a standard 60kW car without fitting a chargecooler is risky. The ECU map pushes boost and timing beyond what the uncooled intake can safely sustain. If you are considering serious performance modifications, understanding the chargecooler’s role is essential before applying an aggressive map — our guide on applying the Brabus SB2 map correctly covers the preconditions that need to be in place for safe, reliable power gains.
For those looking to go further still with a remapped ECU, it is worth knowing that even the Brabus chargecooler has limits. At power levels beyond the stock 74kW, charge temperatures will rise again, and the system’s cooling capacity becomes a constraint. Upgrades to the chargecooler core or coolant pump are worth considering alongside any significant ECU work. Our overview of how MEG ECU remapping works explains the hardware and software interactions that govern how far a tune can safely go.
Common Chargecooler Faults on the Smart Roadster Brabus
Coolant Pump Failure
The electric chargecooler pump is the most common failure point. Symptoms include a noticeable drop in power after a few minutes of spirited driving, with the car recovering once it has cooled down — classic heat soak behaviour. In some cases the pump fails silently, giving no warning other than reduced performance. The pump can be tested by running the engine and feeling whether the chargecooler hoses are circulating warm coolant. A replacement pump is an inexpensive fix that restores full system function.
Low or Contaminated Coolant
The chargecooler has a separate small reservoir that owners sometimes overlook during routine maintenance. Running it low reduces cooling capacity. Contaminated or degraded coolant increases corrosion risk in the aluminium core. The system should be flushed and refilled with a proper aluminium-safe coolant mix during any major service.
Core Blockage or External Fouling
The chargecooler radiator can accumulate debris — leaves, insects, road dirt — reducing airflow and heat rejection. Gentle cleaning with low-pressure water and an appropriate cleaner restores efficiency. Internal blockage of the core itself is rarer but can occur with badly neglected coolant.
Hose Deterioration
As noted above, inspect all chargecooler hoses for cracking, swelling, or weeping at clamps. These are 20-year-old rubber components. Replace proactively rather than waiting for a failure, particularly before any tuning work that will stress the system.
Should You Retrofit a Chargecooler to a Standard 60kW Roadster?
It is technically possible to fit a chargecooler to a non-Brabus Roadster, and some enthusiasts have done so as part of a broader power upgrade project. The benefits are real if you intend to run significantly higher boost — the additional air density and knock resistance open up headroom that the standard intake cannot provide. However, the complexity, cost, and fabrication involved are considerable. You need the core, pump, radiator, hoses, coolant reservoir, and appropriate mounting solutions, all squeezed into an already busy mid-rear engine bay.
For most owners seeking more power from a standard car, a quality ECU remap to the limits the standard hardware can safely support is a more cost-effective first step. If you want to understand what the standard variants can and cannot achieve before committing to hardware modifications, our full comparison of the 45kW, 60kW and Brabus 74kW lays out the factory differences clearly, including the thermal management equipment each variant includes from the factory.
If you are set on Brabus-level performance from a non-Brabus car, buying an actual Brabus and ensuring its chargecooler system is fully serviceable is often the more straightforward route. Our detailed look at whether the Brabus premium is justified covers the real ownership costs and benefits to help you decide.
Maintaining the Brabus Chargecooler: Practical Advice
If you own a Brabus or are buying one, add chargecooler maintenance to your service checklist. Check the coolant reservoir level and condition at every service. Inspect hoses annually. Test the pump operation. Clean the chargecooler radiator externally if it shows any debris accumulation. These are simple tasks that cost very little and make a measurable difference to sustained performance and reliability — particularly important if you are running a remapped ECU that is extracting the maximum the system can give.
For enthusiasts running higher-power maps available through our remapping packages, a fully functioning chargecooler is not optional — it is a prerequisite for the map to deliver its performance safely and consistently. A degraded cooling circuit is the fastest route to inconsistent power and potential engine damage at elevated boost levels.
The Smart Roadster Brabus chargecooler is a small system with an outsized impact on what the 698cc engine can achieve. It is the engineering reason the Brabus can sustain 1.43 bar of boost reliably where the standard car cannot, and it is the foundation on which any serious power upgrade must be built. Keep it maintained, understand how it works, and it will reward you with consistent, heat-soak-free performance. Neglect it, and you will wonder why your Brabus feels no quicker than a 60kW on a warm day.
