BMW 320d vs 320i: Diesel or Petrol in 2026?
320d or 320i is the most-asked question by every UK 3 Series buyer. The answer is annual mileage, ULEZ exposure, and engine-build year. This comparison covers the modern 320d (N47 then B47 diesel) versus modern 320i (N20 then B48 petrol) across F30 and G20 generations, focusing on what actually moves the needle for UK ownership cost.
Quick verdict
320d if you do over 12,000 miles a year and the V5 shows Euro 6 emissions class. Otherwise, 320i is the simpler, ULEZ-from-launch choice with less long-tail service risk. Pre-2015 N47 diesel and pre-2015 N20 petrol both carry timing-chain risk; post-2015 builds (B47 / B48) are the safer used picks regardless of fuel.
Side-by-side comparison
| Dimension | 320d | 320i | Notes |
|---|---|---|---|
| Real-world UK MPG | 48 to 58 mpg combined | 30 to 40 mpg combined | 320d is roughly 1.5x more efficient on long runs. |
| ULEZ compliance | B47 (post-Sept 2014) yes; N47 no | Yes (all builds) | Single biggest London-buyer factor. |
| Timing-chain risk | Pre-2011 N47: high; post-2014 B47: low | Pre-2015 N20: documented; B48: low | Both engines had pre-2015 chain weakness; resolved at successor. |
| Long-term oil filter housing gasket | Standard wear item | Standard wear item | Both engines share modular family OFH gasket pattern. |
| Insurance group (UK) | Group 22 to 28 typically | Group 20 to 26 typically | Petrol slightly cheaper to insure on average. |
| Used buyer pool depth | Largest UK 3 Series pool | Smaller; rare in F30 outside SE / M Sport | Petrol cars are less common but rising on G20. |
| EGR / SCR servicing | EGR recall + NOx sensors (£300-£500 each) | None (petrol) | 320d carries diesel-specific running cost. |
| DPF risk | City-only driving regen failure | N/A (no DPF on petrol) | 320i is the city-bound buyer's pick. |
320d: deeper look
The 320d is the UK's default 3 Series for a reason: 48 to 58 mpg combined, motorway 55 to 65 mpg, 384 to 400 Nm of torque making overtakes effortless. The two engine generations are very different: N47 (2007 to 2014) carries the timing-chain risk that dominates pre-2015 used 320d viewing. B47 (2014 to present) resolved that and added Euro 6 emissions, making post-Sept-2014 builds ULEZ-compliant. Long-tail diesel concerns are the EGR cooler recall NSC R/2018/151 (verify completed) and NOx sensor wear past 60,000 miles (£300 to £500 each).
320i: deeper look
The 320i is the simpler petrol pick: 184 bhp (both N20 and B48 variants), 30 to 40 mpg combined, ULEZ-compliant from launch on every build. The two engine generations share modular-family wear patterns: oil filter housing gasket, PCV diaphragm, electric water pump, intake-valve carbon buildup. Pre-2015 N20 carried similar timing-chain risk to the N47 (the chain stretch story applies to both 4-cylinder modular engines of the period). Post-2015 B48 builds are the cleanest used choice.
Decision logic
Annual mileage is the first filter. Under 8,000 miles per year, 320i wins on total cost of ownership (lower service cost, no diesel-specific wear items, simpler ULEZ story). Over 12,000 miles per year, 320d wins on fuel cost alone (roughly £700 to £1,200 per year saved at current UK pump prices). Between those, the build year matters more: post-2014 B47 320d is the right buy if you can find one; post-2015 B48 320i is the right buy if you can't. Avoid pre-2015 N47 320d and pre-2015 N20 320i unless price reflects timing-chain risk on both.
UK 2026 pricing comparison
| Scenario | 320d | 320i | Notes |
|---|---|---|---|
| 2014 320d M Sport, 80k miles (pre-LCI N47) | £6,000 to £9,000 | £7,500 to £11,000 (320i N20 equivalent) | Pre-LCI; 320i N20 slightly higher due to ULEZ compliance |
| 2017 LCI 320d M Sport, 60k miles (B47) | £12,000 to £15,000 | £12,000 to £15,000 (320i B48 equivalent) | Post-LCI; ULEZ-compliant on both; pricing parity |
| 2020 G20 320d M Sport, 50k miles | £20,000 to £25,000 | £20,000 to £25,000 (320i equivalent) | G20 generation; 320i and 320d at parity |
| 2022 LCI G20 320d M Sport, 30k miles | £26,000 to £30,000 | £26,000 to £30,000 (320i equivalent) | Post-LCI G20; iDrive 8; parity holds |
Recommendation by scenario
| Scenario | Pick | Why |
|---|---|---|
| London commuter (under 6,000 miles annual, inside ULEZ) | 320i | ULEZ-compliant from launch; no DPF risk on short journeys; simpler service profile. |
| UK motorway warrior (over 15,000 miles annual) | 320d (post-2014 B47) | Diesel fuel-cost savings outweigh higher service cost at this mileage. Choose post-2014 build for ULEZ + chain resolution. |
| Family second car (mixed use, 8,000 to 12,000 miles) | 320i B48 or 320d B47 (post-LCI either way) | Either works. 320i wins on simplicity, 320d wins on motorway comfort. Personal preference matters more than spreadsheet. |
| Enthusiast / weekend (low miles, character matters) | 320i | Petrol six-cylinder feel and free-revving character. Skip 318i variants; 320i 184 bhp is the sweet spot. |
| Tight budget (sub-£8,000) | Pre-LCI 320d M Sport with chain documented | Cheapest entry into 3 Series ownership. Verify chain history; reject if not documented and budget doesn't cover the £1,500-£2,500 risk. |
Bimmer.AI is designed to help you identify BMW-specific buyer risks before you travel, negotiate, or pay for an inspection. It does not replace a physical inspection by a qualified mechanic, a legal vehicle-history check (e.g. HPI Check), or independent verification of finance, stolen, or write-off status. Repair-cost ranges are indicative UK figures that vary by region, specialist, parts supply, and labour rates.
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Run a Bimmer.AI buyer report →Frequently asked questions
Is the BMW 320d more expensive to maintain than the 320i?
Yes, modestly. Beyond standard service items, 320d carries diesel-specific costs: EGR cooler recall verification, NOx sensors past 60k miles (£300-£500 each), DPF regen failure on city-only cars (£400-£1,500 if cracked), AdBlue / SCR system on post-2014 builds. 320i has typical modular wear items (OFH gasket, PCV, walnut blast) but no diesel emissions infrastructure. Annual cost difference is around £200 to £500 favouring 320i.
How many miles do I need to do for 320d to be cheaper?
At current UK pump prices and typical 320d (48 to 58 mpg combined) vs 320i (30 to 40 mpg combined), the breakeven is around 10,000 to 12,000 miles per year. Under that, petrol wins on total ownership cost. Over that, diesel pulls ahead on fuel savings alone, even before considering higher 320d service cost.
Is the 320d ULEZ-compliant?
Depends on build date. N47 320d (typically pre-Sept 2014 production) is Euro 5 and NOT ULEZ-compliant. B47 320d (typically post-Sept 2014 production) is Euro 6 and ULEZ-compliant. Verify on the V5 emissions class before purchase. The pre/post-LCI cutoff on F30 (mid-2015) is broadly the same transition window.
Should I buy a pre-2015 320d or post-2015 320i?
Post-2015 320i wins on simplicity and ULEZ. Pre-2015 320d wins on fuel economy if you do high mileage. The risk profile favours the post-2015 320i: no timing-chain conversation, no ULEZ concern, no diesel-specific service items. The pre-2015 320d carries chain risk plus ULEZ issues, but the cheaper purchase price reflects those concerns.
What about the F30 320d EfficientDynamics?
Same N47 (pre-2015) or B47 (post-2015) engine, slightly de-tuned to 163 bhp for emissions and gearing optimised for fuel economy. Same buying logic as regular 320d. The post-2015 320d ED Plus is ULEZ-compliant and delivers around 60 to 65 mpg on a motorway run, the lowest cost of any modern UK 3 Series.
Is the F30 320d N47 chain risk really a deal-breaker?
Not if you verify chain history. Documented chain replacement at an indie BMW specialist (£1,500 to £2,500) puts a pre-2015 N47 320d on equal footing with a post-2015 B47 car. Without receipts, expect to either negotiate the cost into the purchase price OR walk away if the seller refuses.
What's the difference between F30 and G20 320d?
G20 (2019 onwards) uses the B47 engine from the LCI F30 onwards, with mild-hybrid 48V added from 2020. ULEZ compliance is universal across G20. G20 G-chassis is roughly £6,000 to £10,000 more for the same age and mileage; the premium is iDrive 8 (post-2022 LCI), 48V mild-hybrid, and a newer chassis. F30 G20 320d both carry the same B47 engine reliability story.
320d or 330d (the six-cylinder)?
If budget allows, 330d (M57 pre-2014, N57 / B57 LCI / G20) is the family-distance pick. Smoother, faster, around 40 to 50 mpg motorway. Buying decision: 330d is around £2,000 to £5,000 more on F30; on G20 the gap is smaller. Not a fuel-economy decision but a comfort and torque decision.