BMW 4 Series F33Convertible2014–2020
Every engine fitted to the F33 convertible — from the N47 diesel to the N55 straight-six and the B58 that redefined the range.
Real UK replacement costs, honest failure data, and the N20 timing-chain risk that still haunts early four-cylinder petrol cars.
Backed by 256+ real UK F33 enquiries in 2025 [BMW-VERIFIED].
Engine Database
Every engine fitted to the F33 convertible — from the pre‑LCI N‑series units to the post‑LCI B‑series replacements that improved reliability and performance.
Overview
The F33 is the convertible body of BMW's first-generation 4 Series, launched in March 2014 as the direct successor to the E93 3 Series Convertible. It introduced a new naming convention — the 4 Series replacing the 3 Series coupé and convertible — while retaining the E93's three-piece retractable metal hardtop.
The engine range spans from four-cylinder diesels and petrols to the range-topping six-cylinder N55 and B58 units. A 2017 Life Cycle Impulse (LCI) brought significant mechanical updates: the N20 four-cylinder petrol was replaced by the B48, the N55 by the B58, and the N47 diesel was superseded by the B47.
Key Facts
Market Intelligence
The F33 convertible generated 256 real UK engine enquiries in 2025 [BMW-VERIFIED], concentrated on the N20 four-cylinder petrol and N47 diesel units as these cars age out of warranty and timing-chain issues become a significant concern.
04Best & Worst Engines
Best Diesel Overall
B47D20 (2.0-litre diesel, 420d, 2015–2020)
“The B47 replaced the N47 in the 420d and brought the timing chain to the front of the engine — a significant reliability improvement. With 190 bhp and 400 Nm of torque, it delivers strong performance and genuine 50+ MPG economy. It's the diesel to have in an F33.”
Who it's for: Buyers who need diesel economy and torque without the N47's timing-chain anxiety.
Best Petrol Overall
B58B30 (3.0-litre straight-six, 440i, 2016–2020)
“The B58 is BMW's modular straight-six and arguably the best engine ever fitted to a 4 Series. 326–335 bhp, 450 Nm of torque, and a reputation for reliability that rivals Toyota's standards — it's so good Toyota uses it in the Supra. It transforms the F33 into a genuine grand tourer.”
Who it's for: Enthusiasts who want the ultimate F33 engine and are willing to pay for it.
Highest Risk
N20B20 (2.0-litre petrol, 420i/428i/430i, 2014–2017)
“The N20 four-cylinder petrol suffers from timing-chain guide failure — plastic guides become brittle and break, leading to catastrophic engine failure. The chain is located at the rear of the engine, making replacement labour-intensive. Pre-2015 cars are the highest risk.”
Who it's for: Buyers who want an entry-level F33 and have budgeted for timing-chain replacement.
Most Expensive Failure
N20 Timing Chain & Guide Failure
“When the N20's timing chain guides fail, the chain can snap, destroying the engine. A full replacement of chain, guides and tensioner costs £1,500–£2,500 at a specialist; a snapped chain means a full engine replacement at £3,800–£6,000. It's the most expensive non-catastrophic failure in the F33 range.”
Who it's for: Buyers who want to pay for preventative maintenance rather than a replacement.
Best Value
420d with B47 (post-2015)
“The B47-powered 420d delivers 190 bhp, 400 Nm, and 50+ MPG economy — the best all-rounder in the F33 range. It's more reliable than the N47 it replaced, more economical than the six-cylinder cars, and holds its value well. The sweet spot in the range.”
Who it's for: Buyers who want performance, economy and value in one package.
Most Overlooked
430i with B48 (post-LCI, 2017–2020)
“The B48-powered 430i is often overshadowed by the 440i's six-cylinder power and the 420d's economy. But with 252 bhp and a closed-deck design that improves reliability, it's the Goldilocks engine — enough power to be exciting, enough economy to be sensible, and more reliable than the N20 it replaced.”
Who it's for: Buyers who want the best balance of performance, reliability and running costs.
Best Diesel Overall
B47D20
(2.0-litre diesel, 420d, 2015–2020)
“The B47 replaced the N47 in the 420d and brought the timing chain to the front of the engine — a significant reliability improvement. With 190 bhp and 400 Nm of torque, it delivers strong performance and genuine 50+ MPG economy. It's the diesel to have in an F33.”
Who it's for: Buyers who need diesel economy and torque without the N47's timing-chain anxiety.
Best Petrol Overall
B58B30
(3.0-litre straight-six, 440i, 2016–2020)
“The B58 is BMW's modular straight-six and arguably the best engine ever fitted to a 4 Series. 326–335 bhp, 450 Nm of torque, and a reputation for reliability that rivals Toyota's standards — it's so good Toyota uses it in the Supra. It transforms the F33 into a genuine grand tourer.”
Who it's for: Enthusiasts who want the ultimate F33 engine and are willing to pay for it.
Highest Risk
N20B20
(2.0-litre petrol, 420i/428i/430i, 2014–2017)
“The N20 four-cylinder petrol suffers from timing-chain guide failure — plastic guides become brittle and break, leading to catastrophic engine failure. The chain is located at the rear of the engine, making replacement labour-intensive. Pre-2015 cars are the highest risk.”
Who it's for: Buyers who want an entry-level F33 and have budgeted for timing-chain replacement.
Most Expensive Failure
N20
Timing Chain & Guide Failure
“When the N20's timing chain guides fail, the chain can snap, destroying the engine. A full replacement of chain, guides and tensioner costs £1,500–£2,500 at a specialist; a snapped chain means a full engine replacement at £3,800–£6,000. It's the most expensive non-catastrophic failure in the F33 range.”
Who it's for: Buyers who want to pay for preventative maintenance rather than a replacement.
Best Value
420d
with B47 (post-2015)
“The B47-powered 420d delivers 190 bhp, 400 Nm, and 50+ MPG economy — the best all-rounder in the F33 range. It's more reliable than the N47 it replaced, more economical than the six-cylinder cars, and holds its value well. The sweet spot in the range.”
Who it's for: Buyers who want performance, economy and value in one package.
Most Overlooked
430i with B48 (post-LCI, 2017–2020)
“The B48-powered 430i is often overshadowed by the 440i's six-cylinder power and the 420d's economy. But with 252 bhp and a closed-deck design that improves reliability, it's the Goldilocks engine — enough power to be exciting, enough economy to be sensible, and more reliable than the N20 it replaced.”
Who it's for: Buyers who want the best balance of performance, reliability and running costs.
Engine
Typical Mileage
Common Major Failure
Repair Cost (Specialist)
Replacement Cost (Recon)
Ownership Verdict
Risk vs Reward -N47 chain risk applies
Best Diesel -front-mounted chain, improved reliability
Highest Risk -the defining F33 petrol riskSolid Choice -reliable, refined, closed-deck designBest Pre-LCI Six -robust but has known issuesBest Petrol -the most reliable F33 engineEngineTypical MileageCommon Major FailureRepair Cost (Specialist)Replacement Cost (Recon)Ownership VerdictRisk vs Reward -N47 chain risk appliesBest Diesel -front-mounted chain, improved reliabilityHighest Risk -the defining F33 petrol riskSolid Choice -reliable, refined, closed-deck designBest Pre-LCI Six -robust but has known issuesBest Petrol -the most reliable F33 engine
The F33 rule
A £3,800–£6,000 N20 recon against a £10,000–£25,000 F33 sits at 15–60% of the car's value -a significant decision. On a sub-£10,000 high-mileage example, that brushes our 70% BMW threshold -we'll honestly tell you to walk away. Against a well-kept £18,000+ example, the same recon drops to a routine 21–33% -a repair decision, not a financial one. The convertible roof mechanism also adds a unique cost dimension to F33 ownership.
Key Takeaways
Which F33 Costs Least To Own?
430i (B48) -reliable four-cylinder petrol, simpler than six-cylinder, no DPF.
Which F33 Costs Most To Own?
435i (N55) -HPFP, VANOS and oil leaks add up; six-cylinder fuel consumption.
Which F33 Is Best Value?
440i (B58) -the best engine in the range, strongest residuals, the one enthusiasts want.
N20
Timing Chain Guide Failure
Affected models:
F33 420i, 428i, 430i (N20B20, 2014–2017).
Typical failure mileage:
40,000–80,000 miles.
Root cause:
The N20 engine uses plastic timing chain guides that become brittle and crack over time. When these guides fail, the chain can stretch, skip teeth, or snap entirely. The chain is located at the rear of the engine, making inspection and replacement labour-intensive. Low engine oil levels accelerate the problem. Cold-start rattle is the classic early warning.
Tiered Cost Table
Dealer
Dealer
Specialist
Specialist
Dealer
Specialist
Our Recommendation
At the first sign of cold-start rattle or a check engine light, have the timing chain inspected immediately. A £1,500–£2,500 preventative repair is dramatically cheaper than the £3,800–£6,000 replacement that follows if the chain snaps. On an F33 worth under £10,000, this decision alone determines whether the car stays economically viable.
N47
Diesel Timing Chain Stretch
Affected models:
F33 420d (N47D20C, 2014–2015).
Typical failure mileage:
60,000–100,000 miles.
Root cause:
The N47's rear-mounted timing chain receives the last oil feed and is tensioned by a plastic guide that degrades over time. Cold-start rattle for 1–2 seconds is the classic early warning. BMW extended the warranty on N47 timing chains to 7 years/75,000 miles, acknowledging the issue.
Tiered Cost Table
Dealer
Dealer
Specialist
Specialist
Dealer
Specialist
Our Recommendation
At the first sign of cold-start rattle, get the chain inspected immediately -a £650–£1,800 preventative repair is dramatically cheaper than the £3,200+ replacement that follows if ignored. Consider a post-2015 B47-equipped 420d instead.
F33
Retractable Hardtop Mechanism Issues
Affected models:
All F33 convertibles (2014–2020).
Typical failure mileage:
Not mileage-dependent -age and use-related.
Root cause:
The F33's three-piece retractable metal hardtop weighs approximately 250 kg and relies on complex hydraulic and electrical systems. Common issues include water ingress into the rear compartment due to blocked drainage holes, amplifier failure from water damage, roof operation problems, and boot release failures.
Tiered Cost Table
Dealer
Dealer
Specialist
Specialist
Dealer
Specialist
Our Recommendation
Have the roof drainage holes checked and cleared regularly -a £100–£300 preventative service is dramatically cheaper than the £1,200+ repair that follows if water ingress destroys the amplifier or roof motor. Check for water sloshing noises in the rear passenger compartment.
N55
HPFP & Oil Leak Issues
Affected models:
F33 435i (N55B30, 2014–2016).
Typical failure mileage:
50,000–100,000 miles.
Root cause:
The N55's high-pressure fuel pump can fail, causing long cranking and loss of power. Oil leaks from the oil filter housing and valve cover gaskets are common. Brake vacuum pump failure is another known issue. Rod bearing failures have been reported in track use.
Tiered Cost Table
Dealer
Dealer
Specialist
Specialist
Dealer
Specialist
Our Recommendation
If your 435i has no documented HPFP history, budget for replacement as preventative maintenance -£700–£1,500 now is far cheaper than the £4,500+ replacement that follows if the engine runs lean or suffers bearing failure. Regular oil changes at 8,000-mile intervals are essential.
VariantEngine Code
Used (Supply)
Reconditioned (Supply)
Rebuilt (Supply)
Labour HoursScope note: All variants listed are F33 convertible only -the two-door, four-seat convertible produced from 2014 to 2020. F32 Coupé and F36 Gran Coupé are covered on their own Generation Pages, as fitment and labour access vary by body style. M4 (F83) is covered separately.
Most Requested Engines (2025)
Most Requested Variants
Average Replacement Cost
£3,200–£7,500
reconditioned, supply only
[BMW‑QUOTE]
Most Common Failures
Live FeedBMW 430i
F33
ManchesterCold-start rattle, timing chain inspection6
enquiries
Updated MonthlyBMW 420d
F33
BirminghamEngine warning light, EGR valve inspection4
enquiries
Updated MonthlyBMW 440i
F33
LondonCooling system check, water pump replacement3
enquiries
Updated MonthlyMost Requested Engines (2025)
Most Requested Variants
Average Replacement Cost
£3,200–£7,500
reconditioned, supply only
[BMW‑QUOTE]
Most Common Failures
Most Requested Engines (2025)
Most Requested Variants
Average Replacement Cost
£3,200–£7,500
reconditioned, supply only
[BMW‑QUOTE]
Most Common Failures
Scope note: All variants listed are F33 convertible only -the two-door, four-seat convertible produced from 2014 to 2020. F32 Coupé and F36 Gran Coupé are covered on their own Generation Pages, as fitment and labour access vary by body style. M4 (F83) is covered separately.
Most Requested Engines (2025)
Most Requested Variants
Average Replacement Cost
£3,200–£7,500
reconditioned, supply only
[BMW‑QUOTE]
Most Common Failures
Most Requested Engines (2025)
Most Requested Variants
Average Replacement Cost
£3,200–£7,500
reconditioned, supply only
[BMW‑QUOTE]
Most Common Failures
Most Requested Engines (2025)
Most Requested Variants
Average Replacement Cost
£3,200–£7,500
reconditioned, supply only
[BMW‑QUOTE]
Most Common Failures
Live FeedBMW 430i
F33
ManchesterCold-start rattle, timing chain inspection6
enquiries
BMW 420d
F33
BirminghamEngine warning light, EGR valve inspection4
enquiries
BMW 440i
F33
LondonCooling system check, water pump replacement3
enquiries
Updated MonthlyTrusted F33 Engine Suppliers
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