BMW 3 Series G20Saloon2018–2026
Every engine fitted to the seventh-generation 3 Series G20 saloon — from the 2.0-litre B48 four-cylinder to the 3.0-litre B58 six-cylinder, the plug-in hybrid 330e and the range-topping M340i.
Real UK costs, honest reliability data, and BMW's modular engine family at its best.
Backed by 190+ real UK G20 enquiries in 2025 [BMW-VERIFIED].
Engine Database
Every engine fitted to the G20 saloon specifically — from the entry-level 318i to the M340i, including the B48-to-B58 modular engine family and the plug-in hybrid 330e.
Overview
The seventh-generation BMW 3 Series (codenamed G20 for the saloon) was unveiled at the 2018 Paris Motor Show on 2 October 2018 and entered production later that month. Built on BMW's CLAR platform, the G20 marked a significant evolution over the F30 — lighter, stiffer and more technologically advanced. The engine range launched with 2.0-litre B48 four-cylinder petrols (320i, 330i) and the 3.0-litre B58 six-cylinder (M340i), joined by B47 four-cylinder and B57 six-cylinder diesels.
A plug-in hybrid 330e arrived in 2019, and a July 2022 facelift (LCI) brought mild-hybrid technology to the range. The M3 (G80), based on the G20 platform, uses the S58 engine and is covered on its own Generation Page.
Key Facts
Market Intelligence
The G20 saloon generated 190 real UK engine enquiries in 2025 [BMW-VERIFIED], concentrated on the 320i and 330i as the most popular UK variants.
04Best & Worst Engines
Best Petrol Overall
B48B20B -330i (2018–2026)
“The B48 is BMW's most refined four-cylinder — smooth, responsive and genuinely reliable. The 330i's 258 PS is the sweet spot: more powerful than the 320i, but without the complexity or running costs of the six-cylinder M340i.”
Who it's for: buyers who want the best all-round G20 petrol.
Highest Risk
B48B20A (PHEV) — 330e
“The 330e adds complexity — electric motor, battery pack and charging system — to the otherwise robust B48. Battery health and charging system reliability are the key concerns; hybrids are more complex to maintain.”
Who it's for: buyers who want company-car tax benefits and are prepared for hybrid-specific maintenance.
Most Expensive Failure
S58B30A -M3/M3 Competition
“The S58 is a high-performance engine with significant complexity — twin turbos, high-pressure fuel system and M-specific components. Repairs are specialist-only and expensive; full replacement costs £8,000–£14,000.”
Who it's for: enthusiasts who want 510 PS and are ready for the bills that come with it.
Best Value
B48B20A -320i (2018–2026)
“The 320i is the most common G20 petrol — reliable, efficient and well-supported. A £2,800–£4,500 recon makes sense against a £15,000–£30,000 vehicle.”
Who it's for: buyers who want the most cost-effective G20 ownership.
Most Overlooked
B47D20B -320d
“The B47 is a significant improvement over the N47 — timing chain issues are far less common, and EGR cooler problems are well-documented and manageable. The 320d offers excellent economy without the petrol's fuel bills.”
Who it's for: buyers who want diesel economy and don't need six-cylinder pace.
Best Petrol Overall
B48B20B
-330i (2018–2026)
“The B48 is BMW's most refined four-cylinder — smooth, responsive and genuinely reliable. The 330i's 258 PS is the sweet spot: more powerful than the 320i, but without the complexity or running costs of the six-cylinder M340i.”
Who it's for: buyers who want the best all-round G20 petrol.
Highest Risk
B48B20A
(PHEV) — 330e
“The 330e adds complexity — electric motor, battery pack and charging system — to the otherwise robust B48. Battery health and charging system reliability are the key concerns; hybrids are more complex to maintain.”
Who it's for: buyers who want company-car tax benefits and are prepared for hybrid-specific maintenance.
Most Expensive Failure
S58B30A
-M3/M3 Competition
“The S58 is a high-performance engine with significant complexity — twin turbos, high-pressure fuel system and M-specific components. Repairs are specialist-only and expensive; full replacement costs £8,000–£14,000.”
Who it's for: enthusiasts who want 510 PS and are ready for the bills that come with it.
Best Value
B48B20A
-320i (2018–2026)
“The 320i is the most common G20 petrol — reliable, efficient and well-supported. A £2,800–£4,500 recon makes sense against a £15,000–£30,000 vehicle.”
Who it's for: buyers who want the most cost-effective G20 ownership.
Most Overlooked
B47D20B -320d
“The B47 is a significant improvement over the N47 — timing chain issues are far less common, and EGR cooler problems are well-documented and manageable. The 320d offers excellent economy without the petrol's fuel bills.”
Who it's for: buyers who want diesel economy and don't need six-cylinder pace.
Engine
Typical Mileage
Common Major Failure
Repair Cost (Specialist)
Replacement Cost (Recon)
Ownership Verdict
Solid Choice -reliable B48Best Petrol -B48 is a modern classic
Watch Closely -hybrid complexityBest Six -B58 is a future classicSolid Choice -improved over N47Solid Choice -six-cylinder diesel refinementEngineTypical MileageCommon Major FailureRepair Cost (Specialist)Replacement Cost (Recon)Ownership VerdictSolid Choice -reliable B48Best Petrol -B48 is a modern classicWatch Closely -hybrid complexityBest Six -B58 is a future classicSolid Choice -improved over N47Solid Choice -six-cylinder diesel refinement
The G20 rule
A £3,200–£5,000 B48 recon against a £15,000–£35,000 G20 sits at 9–33% of the car's value -well within our 70% BMW threshold. Even against a sub-£12,000 high-mileage example, the same recon is 27–42% -a repair decision, not a financial one. The G20 holds value well enough that engine replacement is almost always viable.
B48/B58
Cooling System
Affected models:
G20 318i, 320i, 330i, M340i (all B-series engines, 2018–2026).
Typical failure mileage:
60,000–100,000 miles.
Root cause:
The B-series modular engines are generally reliable, but cooling system components -water pump, expansion tank, plastic fittings -can develop leaks. This is the most common B-series failure point across the range.
Tiered Cost Table
Preventative (Repair)
Dealer
Specialist
£600–£1,200
£400–£900
Catastrophic (Replacement)
Dealer
Specialist
£3,500–£5,500
£2,800–£4,500
Our Recommendation
On any B-series G20 approaching 60,000 miles, have the cooling system inspected -a £400–£900 preventative repair is cheaper than the £2,800+ replacement that follows an overheating failure.
B47
Diesel EGR Cooler
Affected models:
G20 318d, 320d (B47 diesel, 2018–2026).
Typical failure mileage:
60,000–120,000 miles.
Root cause:
The B47 diesel's EGR cooler can develop internal leaks, allowing coolant into the exhaust. This is a known issue across BMW's B47 engine family. The B47 is otherwise a significant improvement over the N47 -timing chain issues are far less common.
Tiered Cost Table
Preventative (Repair)
Dealer
Specialist
£600–£1,200
£400–£900
Catastrophic (Replacement)
Dealer
Specialist
£4,000–£6,500
£3,200–£5,500
Our Recommendation
At the first sign of coolant loss or white smoke, get the EGR cooler inspected -a £400–£900 repair is cheaper than the £3,200+ replacement that follows if ignored.
330e
Hybrid Battery & Charging System
Affected models:
G20 330e (PHEV, 2019–2026).
Typical failure mileage:
60,000–100,000 miles.
Root cause:
The 330e adds significant complexity -a 12 kWh lithium-ion battery pack, electric motor and charging system. Battery degradation and charging system faults are the primary concerns. The internal combustion engine (B48) is robust, but the hybrid system requires specialist attention.
Tiered Cost Table
Preventative (Repair)
Dealer
Specialist
£800–£1,500
£500–£1,200
Catastrophic (Replacement)
Dealer
Specialist
£5,000–£8,000
£3,500–£5,500
Our Recommendation
If you're buying a 330e, have a full battery health check and charging system inspection before purchase. Hybrid components can be expensive to replace -factor this into your ownership budget.
VariantEngine Code
Used (Supply)
Reconditioned (Supply)
Rebuilt (Supply)
Labour HoursNo Generation variance from the Engine Page baseline -no dedicated Engine Pages exist for these families yet, so baseline figures are drawn from the EM_Proprietary_Data Table A. Labour hours estimated at 10–14 hours for four-cylinder engines, 12–16 hours for six-cylinder engines, and 16–22 hours for the M3's S58 due to additional complexity.
Scope note: All variants listed are G20 saloon only. The G21 Touring and G28 long-wheelbase saloon share most of these engines but are covered on their own Generation Pages. The M3 (G80) is based on the G20 platform but uses the S58 engine; it is covered on its own Generation Page. The 330e PHEV uses the B48B20A engine with an electric motor.
Most Requested Engines (2025)
Most Requested Variants
Average Replacement Cost
£4,500
reconditioned, supply only
[BMW-QUOTE]
Most Common Failures
Live FeedBMW 320i G20
B48
Manchester
Coolant loss warning5
enquiries
Updated MonthlyBMW 330e G20
B48 PHEV
BirminghamCharging system fault3
enquiries
Updated MonthlyBMW M340i G20
B58
LeedsWater pump failure3
enquiries
Updated MonthlyMost Requested Engines (2025)
Most Requested Variants
Average Replacement Cost
£4,500
reconditioned, supply only
[BMW-QUOTE]
Most Common Failures
Most Requested Engines (2025)
Most Requested Variants
Average Replacement Cost
£4,500
reconditioned, supply only
[BMW-QUOTE]
Most Common Failures
Scope note: All variants listed are G20 saloon only. The G21 Touring and G28 long-wheelbase saloon share most of these engines but are covered on their own Generation Pages. The M3 (G80) is based on the G20 platform but uses the S58 engine; it is covered on its own Generation Page. The 330e PHEV uses the B48B20A engine with an electric motor.
Most Requested Engines (2025)
Most Requested Variants
Average Replacement Cost
£4,500
reconditioned, supply only
[BMW-QUOTE]
Most Common Failures
Most Requested Engines (2025)
Most Requested Variants
Average Replacement Cost
£4,500
reconditioned, supply only
[BMW-QUOTE]
Most Common Failures
Most Requested Engines (2025)
Most Requested Variants
Average Replacement Cost
£4,500
reconditioned, supply only
[BMW-QUOTE]
Most Common Failures
Live FeedBMW 320i G20
B48
ManchesterCoolant loss warning5
enquiries
BMW 330e G20
B48 PHEV
BirminghamCharging system fault3
enquiries
BMW M340i G20
B58
LeedsWater pump failure3
enquiries
Updated MonthlyTrusted G20 Engine Suppliers
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