BMW builds two superb 3.0-litre straight-sixes from the same modular family, and the only real decision between them is what goes in the tank. The B58 is the petrol — the engine famous enough that Toyota borrowed it for the Supra. The B57 is the diesel — quieter about its talents, but a 400 hp long-distance machine.
This isn't a reliability rescue mission like some comparisons. Both are excellent. It's a lifestyle question dressed up as an engineering one.
Quick answer: The B58 (93/100, BEST) is one of the finest petrol sixes BMW has ever made and the higher score here. The B57 (80/100, BUY) is a rock-solid diesel for high-mileage drivers. Choose by your annual kilometres and the kind of driving you love — not by the score gap.
The star: B58 — 93/100 (BEST)
The B58 (2015→) is a modern classic. Smooth, endlessly tunable, and trusted enough that Toyota put it in the GR Supra. At 93/100 it's near the very top of our petrol rankings, and its faults are almost charmingly minor:
| Problem | Severity | Repair cost |
|---|---|---|
| Coolant expansion tank / line (early units) | Moderate | €150–350 |
| Valve cover gasket oil leak | Minor | €200–450 |
| Plastic charge pipe crack | Minor | €80–200 |
There's nothing on this list that should worry you. These are the small, cheap, well-understood items of a fundamentally sound design.
Found in: BMW 340i, 440i, 540i, M240i, M340i, X3 M40i, Z4 M40i — and the Toyota GR Supra.
The workhorse: B57 — 80/100 (BUY)
The B57 (2016→) is the diesel side of the same coin: up to 400 hp, vast torque, and a real-world range that petrol drivers can only dream about. In our database it carries no documented major faults — a clean record for an engine built to cover huge distances.
What it asks in return is the modern-diesel deal: AdBlue/SCR emissions hardware and a preference for long runs over short urban hops to keep the DPF happy.
Found in: BMW 530d, X5 30d.
Same block, different jobs
| B58 (petrol) | B57 (diesel) | |
|---|---|---|
| Fuel | Petrol turbo | Diesel turbo |
| Power | ~387 hp | up to 400 hp |
| Score | 93/100 | 80/100 |
| Verdict | BEST | BUY |
| Best for | Driving pleasure, tuning | Long-distance economy |
Which one should you buy?
Forget the 13-point gap for a second — it reflects the B58 being an exceptional petrol engine, not the B57 being weak. Decide on use:
- Under ~15,000 km a year, mostly mixed/urban, and you enjoy driving? The B58. It's smoother, sounds better, doesn't care about short trips, and is one of the most rewarding sixes on the road.
- High annual mileage, lots of motorway, towing or long commutes? The B57. The diesel economy and range will pay you back, and the DPF stays healthy on the open road.
Both are engines you can buy with confidence. The "wrong" choice here is only wrong for your driving — not for your peace of mind.
Want the diesel-vs-diesel angle instead? See B57 vs M57, old BMW oil-burner against new.
Scores are calculated from documented issues, repair costs, and failure patterns. Reviewed by the EngineScope editorial team. Methodology →