The E39 523i

Engine

The BMW E39 523i was powered by the M52B25 engine, a 2.5-liter inline-six (I6) that offered a balance between performance, refinement, and efficiency. Part of BMW's M52 engine family, it featured an aluminum block with Nikasil-coated cylinder liners (later replaced with steel liners in certain markets) and VANOS variable valve timing, ensuring smooth power delivery across the rev range.

With the E39 facelift in 2000, the M52B25 was replaced by the M54B25, which retained the same displacement but introduced electronic throttle control, revised intake and exhaust systems, and improved engine management. These refinements enhanced reliability, fuel efficiency, and mid-range torque, making the facelifted 523i a more refined driving experience.

Although not the most powerful model in the E39 lineup, the 523i was appreciated for its balance of performance and economy, offering stronger acceleration than the 520i while maintaining better efficiency than the 528i or 530i. Its smooth-revving nature and reliability have made it a favorite among enthusiasts who appreciate BMW's classic inline-six character.


Performance

The 523i sat comfortably between the 520i and 528i, offering a well-rounded mix of power and efficiency. Its M52B25 engine produced 170 hp (125 kW) at 5,500 rpm and 245 Nm (181 lb-ft) at 3,950 rpm, giving it a little bit better performance than the 520i while still maintaining decent fuel economy.

With the facelift, the M54B25 increased power slightly to 174 hp (128 kW) at 6,000 rpm, though peak torque remained similar at 245 Nm (181 lb-ft) at 3,500 rpm. The updated engine provided a smoother and more responsive throttle feel, along with improved fuel management.

While the 523i was not designed as a high-performance model, it delivered refined acceleration and a strong mid-range, making it an excellent option for those who valued driving pleasure without excessive fuel consumption.

Specs:

Pre-Facelift (M52B25, 2.5L I6)

  • Power Output: 170 hp (125 kW) @ 5,500 rpm
  • Torque: 245 Nm (181 lb-ft) @ 3,950 rpm
  • 0-100 km/h (0-62 mph) Acceleration: ~8.5 seconds (manual)
  • Top Speed: ~230 km/h (143 mph)

Facelift (M54B25, 2.5L I6)

  • Power Output: 174 hp (128 kW) @ 6,000 rpm
  • Torque: 245 Nm (181 lb-ft) @ 3,500 rpm
  • 0-100 km/h (0-62 mph) Acceleration: ~8.0 seconds (manual)
  • Top Speed: ~233 km/h (145 mph)

523i Sound


523i Acceleration

Fuel Efficiency

Pre-Facelift (M52B25, 2.5L I6)

  • Combined: ~8.5–9.5 liters per 100 km (25–28 mpg)
  • Urban: ~11.5–12.5 liters per 100 km (19–21 mpg)
  • Extra-Urban: ~6.5–7.5 liters per 100 km (31–36 mpg)
  • Fuel Tank Capacity: 70 liters (18.5 gallons)

Facelift (M54B25, 2.5L I6)

  • Combined: ~8.0–9.0 liters per 100 km (26–29 mpg)
  • Urban: ~11.0–12.0 liters per 100 km (19–22 mpg)
  • Extra-Urban: ~6.0–7.0 liters per 100 km (34–39 mpg)
  • Fuel Tank Capacity: 70 liters (18.5 gallons)


Reliability

The M52B25 is particularly durable, with fewer electronic components compared to later BMW engines. However, early Nikasil-coated cylinder liners had issues in markets with high-sulfur fuel, though most affected engines have either been replaced or continue to run without major issues.

The M54B25, while refined, introduced a few common issues such as oil consumption, DISA valve failures, and cooling system weaknesses. Despite this, proper maintenance can ensure long-term reliability, with many M54 engines surpassing 400,000 km (250,000 miles) without major problems.