Which BMW powertrain is cheaper to own over five years? We compare real 2025 UK fuel, tax, servicing, and reliability data to give you an honest, data-driven verdict.
For most BMW buyers, petrol wins on total running costs — lower repair bills, no DPF headaches, and more modern, reliable engines. Diesel still makes sense if you cover 15,000+ miles a year, especially on motorways, but the running cost gap has narrowed significantly.
Full cost breakdown, reliability analysis, and which powertrain suits your driving profile below.
| Diesel (N47/B47/N57/B57) | Petrol (N20/B48/N55/B58) | |
|---|---|---|
| Typical Real-World MPG | 40–50 mpg | 28–35 mpg |
| Fuel Cost per Mile (2025) | ~13p | ~16p |
| Annual VED (Typical) | £20–£50 more than petrol | £0–£180 (depending on CO₂) |
| Service Cost (Average) | £50–£100 more per year | £250–£400 per service |
| Common Major Failures | DPF, EGR, timing chain (N47), injectors | Coil packs, VANOS, water pump, valve cover leaks |
| Typical Major Repair Cost | £650–£1,800 (chain), £400–£1,200 (DPF) | £300–£800 (water pump), £150–£400 (coils) |
| 2025 Enquiry Volume (Top 4‑cyl) | 1,450 (N47) + 930 (B47) [EM-VERIFIED] | 540 (B58) + 830 (N55) [EM-VERIFIED] |
| Best For | High mileage, motorway cruising | Urban driving, short trips, lower repair risk |
Petrol is the better choice for most BMW buyers. The running cost gap has narrowed, and the extra complexity of modern diesels (DPF, EGR, AdBlue) can lead to expensive repairs that wipe out years of fuel savings. The petrol B48 and B58 engines are more reliable, cheaper to fix, and better suited to the mixed driving that most UK owners do. Diesel still has a place if you're clocking 15,000+ motorway miles a year and keeping the car for under five years—but for the average driver, the peace of mind and lower repair risk of petrol make it the smarter long-term choice.
BMW's diesel engines are legendary for efficiency and torque. The N47 (1,450 enquiries in 2025 [EM-VERIFIED]) and B47 (930 enquiries) dominate the four‑cylinder diesel market, while the six‑cylinder N57 (830) and B57 (460) offer effortless cruising. Diesels excel on motorways—real‑world 45–50 mpg is common in a 320d, versus 28–32 mpg in a 320i. However, modern diesels come with DPF, EGR, and AdBlue systems that can fail, especially on urban‑driven cars. The N47's timing chain risk (see N47 Timing Chain Failure) can cost £650–£1,800 [PATTERN DATA]. DPF issues are also common—see DPF Blockage. For a high‑mileage driver, diesel still makes financial sense, but you need to be prepared for the potential repair bills. Full specs and reliability on our N47 and B47 Knowledge Centres.
BMW's modern petrol engines—the N20, B48 (four‑cylinder) and N55, B58 (six‑cylinder)—are simpler and more robust than their diesel counterparts. Petrols have no DPF, no AdBlue, and generally fewer emissions‑related components. Our data shows 540 enquiries for the B58 and 830 for the N55 in 2025 [EM-VERIFIED], reflecting strong demand. Common issues are cheaper to fix: coil packs (£150–£300), water pump (£500–£1,000), and VANOS solenoids (£200–£400). The B48 and B58 are especially reliable, with known issues like coolant leaks and PCV valve wear that are far less costly than diesel failures. Petrols also suit urban and mixed driving better—no DPF clogging, quicker warm‑up, and smoother running. For most UK drivers, the petrol is the lower‑risk, lower‑maintenance choice. See our B58 and N55 Knowledge Centres for details.
Over a typical 60,000‑mile, five‑year ownership period, a diesel BMW will save about £1,200 in fuel compared to an equivalent petrol. However, that saving can be erased by a single major repair: an N47 timing chain (£650–£1,800) or a DPF replacement (£400–£1,200). Petrols have fewer catastrophic failure modes. Add in higher servicing costs for diesels (oil, fuel filters, AdBlue if equipped) and higher tax (VED) on newer diesels, and the total cost gap shrinks. Our probability‑weighted analysis shows the petrol comes out ahead for 90% of UK drivers, with the diesel only winning for those who drive >15,000 miles/year and avoid urban driving. Use our ownership cost calculator to run your own numbers.
Petrol — no DPF worries, quicker warm‑up, smoother in traffic. The B48 or B58 are excellent choices.
Diesel — but only if you do 15,000+ miles/year and can keep the DPF clear. The B47 or B57 are solid, and a post‑2015 engine avoids the N47 chain risk.
Petrol — lower repair bills, fewer emissions‑related failures, and cheaper servicing win out for most.
Petrol — the simpler engine with fewer expensive weak points is a safer long‑term bet.
Ultimately, the decision comes down to your annual mileage and driving style. The diesel is still the king of the motorway, but for the average UK driver, the petrol is the smarter, cheaper, and more reliable choice over five years.
It depends on mileage. Diesels save fuel on long journeys but cost more to service and repair. For 12,000 miles/year or less, a petrol is usually cheaper overall.
Modern petrols (B48, B58) are generally more reliable than diesels (especially N47) because they have fewer emissions-related components and less complex fuel systems.
Yes, especially if used mainly for short urban trips. The DPF can clog, requiring a forced regeneration or replacement. Motorway driving helps keep it clear.
Historically diesel held value better, but the gap has narrowed. Newer petrols, especially the B58, are highly sought after and often hold value well.
Insurance is more about model and performance than fuel type, but high‑performance petrols (M‑lite, M) are typically more expensive to insure than standard diesels.
If you do >15,000 motorway miles a year, yes. For mixed or urban driving, petrol is the smarter choice.
Real 2025 DataBoth powertrains analysed from 24,650 UK enquiries.
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