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The BMW 6 Series E64 635i is a luxury convertible that combines elegant design with impressive performance, offering a smooth and enjoyable driving experience. Powered by the N54 3.0-liter twin-turbocharged inline-six engine, the 635i delivers a balanced blend of power and efficiency. However, like any vehicle, the E64 635i has its share of common issues that owners should be aware of. Understanding these problems can help maintain the vehicle in optimal condition and avoid costly repairs.
BMW 6 Series E64 635i Engine Performance Issues
The BMW 6 Series E64 635i is equipped with the N54 engine, which is known for its strong performance and responsiveness. However, this engine is also known for several common issues. One of the most significant problems is related to the high-pressure fuel pump (HPFP). The HPFP in the N54 engine is prone to failure, leading to symptoms such as long cranking times, engine misfires, and loss of power. When the HPFP fails, it can trigger the check engine light and cause the vehicle to enter limp mode, significantly reducing its performance. BMW has issued recalls and extended warranties to address this issue, but it remains a concern for owners. Replacing the HPFP as soon as symptoms appear is crucial to maintaining engine performance.
Another common issue with the N54 engine is the failure of the fuel injectors. Over time, the fuel injectors can become clogged or start leaking, leading to uneven fuel delivery and poor engine performance. Symptoms of failing fuel injectors include rough idling, poor acceleration, and increased fuel consumption. In some cases, the injectors may need to be replaced to restore proper engine function. Regular maintenance and the use of high-quality fuel can help reduce the likelihood of injector problems.
The N54 engine is also known for turbocharger issues. The twin-turbo setup provides excellent power, but the turbos can develop problems, particularly with the wastegates. The wastegates control the flow of exhaust gases to the turbochargers, and when they fail, it can lead to turbo lag, poor acceleration, and increased exhaust noise. In severe cases, the turbos themselves may need to be replaced. Symptoms of turbocharger failure include a noticeable loss of power, a whistling noise from the turbo, and increased exhaust smoke. Regular maintenance, including timely oil changes with high-quality synthetic oil, can help extend the life of the turbochargers.
Transmission Issues
The BMW 6 Series E64 635i is equipped with a six-speed automatic transmission that generally provides smooth shifting and reliable performance. However, transmission-related issues can arise as the vehicle ages. One of the most commonly reported problems is harsh or delayed shifting, especially when the vehicle is cold or under heavy load. Drivers may notice that the transmission hesitates to shift gears, shifts too late, or engages gears roughly, leading to a less-than-smooth driving experience. This issue can often be linked to the transmission control unit or the condition of the transmission fluid. Over time, the transmission fluid can degrade or become contaminated, leading to poor transmission performance. Regular transmission fluid changes and software updates can help address these issues, but in more severe cases, the transmission control unit may need to be reprogrammed or replaced.
Another issue that some 635i owners have reported is transmission slipping. This occurs when the engine revs increase without a corresponding increase in vehicle speed, which can be particularly dangerous when trying to accelerate or merge into traffic. Transmission slipping can be caused by low or contaminated transmission fluid, worn clutch packs, or internal transmission damage. If the transmission fluid is low or dirty, a fluid change may resolve the issue. However, persistent slipping may indicate a more serious internal issue that requires professional diagnosis and potentially a transmission rebuild or replacement.
Electrical System Problems
The BMW 6 Series E64 635i is equipped with a sophisticated electrical system that controls various aspects of the vehicle’s operation, including the engine, transmission, and infotainment system. While this complexity offers a high level of functionality and convenience, it also increases the likelihood of electrical issues. One of the most common electrical problems reported by owners is related to the vehicle’s battery and charging system. The 635i is known to experience battery drain issues, where the battery loses charge even when the car is not in use. This can be due to various factors, including faulty wiring, malfunctioning control modules, or problems with the comfort access system, which allows for keyless entry and ignition.
The alternator is another component that can fail in the 635i, especially if it is exposed to high temperatures under the hood. A failing alternator can lead to a battery that doesn’t hold a charge, resulting in a car that struggles to start or maintain electrical functions. Symptoms of a failing alternator include dimming headlights, flickering dashboard lights, and warning messages related to the charging system. Regular checks of the battery and charging system, including testing the alternator’s output, can help prevent these issues from occurring.
In addition to battery and charging system problems, the 635i is also prone to issues with its numerous sensors and control units. These sensors and control units monitor and control various aspects of the vehicle’s operation, and when they malfunction, they can trigger warning lights on the dashboard, even when there is no underlying mechanical issue. For example, the tire pressure monitoring system (TPMS) is known to give false readings, indicating a tire is low on pressure when it is not. Similarly, the engine control module (ECM) can store fault codes related to the fuel system or emissions control system, even when there is no actual problem. These electrical gremlins can be difficult and expensive to diagnose and fix, as they often require specialized equipment and expertise to address properly.
Suspension and Steering Issues
The suspension and steering system in the BMW 6 Series E64 635i is designed to provide a smooth and responsive driving experience, but it is not without its issues. One of the most commonly reported problems is related to the front suspension components, particularly the control arm bushings. Over time, these bushings can wear out, leading to a noticeable clunking noise when driving over bumps or during sharp turns. Worn bushings can also cause the vehicle to feel less stable and precise, especially at higher speeds, as the worn bushings allow for more movement in the suspension than intended. This can lead to uneven tire wear, poor handling, and a less comfortable ride. In some cases, the entire control arm assembly may need to be replaced to restore proper handling and ride quality.
Another common suspension issue in the 635i is related to the rear shock absorbers. The shock absorbers are designed to provide a smooth and comfortable ride, but they can wear out over time, leading to a harsh or bouncy ride. Symptoms of failing shock absorbers include increased body roll during cornering, a noticeable decrease in ride comfort, and uneven tire wear. If the shock absorbers fail completely, the vehicle may become difficult to control, particularly during aggressive driving or on rough roads. Regular inspections of the suspension system, including the control arms, bushings, and shock absorbers, are essential to maintain the vehicle’s handling characteristics.
The power steering system in the 635i can also develop issues over time. One common problem is with the power steering pump, which can fail, leading to a loss of power assist and making the steering wheel difficult to turn, especially at low speeds. Leaks from the power steering pump or lines can lead to a loss of power steering fluid, exacerbating the problem. If the power steering fluid level becomes too low, it can cause the power steering pump to overheat and fail, leading to a complete loss of power steering. Regular inspections of the suspension and steering system, including checking for leaks and wear, are essential to maintain the driving dynamics that the 635i is known for.
Cooling System Failures
The cooling system in the BMW 6 Series E64 635i is another area where problems can arise, particularly as the vehicle accumulates mileage. The cooling system is responsible for regulating the engine’s temperature and preventing overheating, but it can develop issues over time. One of the most common problems is with the electric water pump, which is responsible for circulating coolant throughout the engine. Unlike traditional mechanical water pumps, the electric water pump in the N54 engine is prone to failure, often without much warning. When this happens, the engine can quickly overheat, leading to potential damage to the cylinder head, head gasket, or even the engine block. Symptoms of a failing water pump include the engine temperature rising rapidly, coolant leaks, and warning lights related to the cooling system appearing on the dashboard.
In addition to the water pump, the thermostat is another component of the cooling system that can fail. The thermostat regulates the engine’s temperature by controlling the flow of coolant, and if it becomes stuck in the open or closed position, it can cause the engine to run too hot or too cold. This can affect performance and fuel efficiency and lead to increased wear on the engine components. A stuck thermostat can also reduce the lifespan of the engine. Replacing the thermostat as part of regular cooling system maintenance can help prevent this issue from occurring.
The cooling system in the 635i also includes several plastic components, such as the radiator, coolant hoses, and expansion tank, which can become brittle and crack over time. These components are particularly prone to failure in older vehicles or those that have been exposed to extreme temperatures. If any of these components fail, it can lead to coolant leaks and the risk of overheating. Regular maintenance of the cooling system, including timely replacement of the water pump, thermostat, and coolant, can help prevent these issues and keep the engine running at the proper temperature.
Fuel System Problems
The fuel system in the BMW 6 Series E64 635i, while generally reliable, can develop issues that affect the vehicle’s performance and drivability. One common problem is related to the fuel injectors, which can become clogged or leak over time. Clogged fuel injectors can lead to uneven fuel delivery, causing the engine to run lean, which can result in increased exhaust emissions, reduced fuel economy, and potential damage to the catalytic converter. On the other hand, leaking injectors can cause the engine to run rich, leading to black smoke from the exhaust, poor fuel economy, and increased wear on the engine components. In some cases, the injectors may need to be cleaned or replaced to restore proper function.
Another fuel system issue that can occur is related to the fuel pump. The fuel pump is responsible for delivering fuel from the tank to the engine, and if it fails, it can lead to a loss of power, engine stalling, or even a no-start condition. Symptoms of a failing fuel pump include difficulty starting the engine, hesitation during acceleration, and a noticeable drop in performance. If the fuel pump is not replaced promptly, it can lead to more serious issues, such as damage to the fuel injectors or engine components.
The fuel filter is another component of the fuel system that can cause problems if it becomes clogged with debris. A clogged fuel filter can restrict fuel flow to the engine, causing a loss of power and efficiency. If the fuel filter is not replaced regularly, it can lead to more serious issues, such as damage to the fuel pump or fuel injectors. Regular maintenance of the fuel system, including timely replacement of the fuel injectors, fuel pump, and fuel filter, is essential to avoid these problems and ensure the vehicle continues to run smoothly.
Conclusion
The BMW 6 Series E64 635i is a luxurious and stylish convertible that offers a refined driving experience with its powerful inline-six engine and well-balanced chassis. However, like any car, it is not without its common problems. From engine performance issues and transmission problems to electrical system glitches and cooling system failures, these issues can be costly and inconvenient if not addressed promptly. Regular maintenance and attention to the early signs of trouble can help keep these problems at bay and ensure that your 635i continues to deliver the performance and luxury that BMW is known for. If you’re experiencing any of these issues or need expert advice and service, visit our workshop, European Auto Pro, located at 253 Goodwood Road, Kings Park, 5034 South Australia. Our team of skilled technicians is here to help you maintain your BMW in top condition.