BMW 4 Series 420i2013–presentN20 / B48 2.0 Turbo

BMW 4 Series 420i Engine Replacement —Compare Prices &
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Name: BMW 4 Series 420i UK Engine Enquiry Data 2025
Creator: BMWEngines.uk

Get quotes today from trusted UK BMW 420i specialists. Compare reconditioned, rebuilt and used N20 and B48 2.0-litre turbocharged engines — supply & fit available nationwide for this sleek premium coupé.

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BMW 4 Series 420i Engines — from £1,800 to £7,500Common codes: N20B20, B48B20

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The 4 Series 420i Through Time — Era Map

Two generations. Two eras. One guide to reliability, costs and what really matters.

Era Note

N20 era — timing chain tensioner is the defining weak point; 2016+ revisions improved durability

Era Note

Modern B48 — timing chain at the front, significantly improved durability; coolant and PCV are the main watchpoints

Generation	Years	Engine Code	Reliability	Recon Cost (Guide)	Era Note
4 Series F32/F33/F36	2013–2020	N20B20(2.0L 4-cyl turbo, 184 bhp)		£3,200–£6,500[PLACEHOLDER]	N20 era — timing chain tensioner is the defining weak point; 2016+ revisions improved durability
4 Series G22/G23/G26	2020–present	B48B20(2.0L 4-cyl turbo, 184 bhp)		£3,500–£7,500[PLACEHOLDER]	Modern B48 — timing chain at the front, significantly improved durability; coolant and PCV are the main watchpoints

Why use this era map?

Every cost guide, reliability rating and engine code on this page is aligned to the data above. This keeps everything consistent and trustworthy.

Real UKCost Data
VerifiedReliability
ExpertInsights
Updated for2025

BMW 4 Series 420i Engine Replacement Costs

Supply Only£3,200 – £6,500
Fitted (Indie)£4,200 – £7,800
Warranty12–24 months
Best ForMost owners — best cost/warranty balance

Engine Type	Supply Only	Fitted (Indie)	Warranty	Best For
Used Engine	£1,800 – £3,200	£2,600 – £4,500	1–6 months	Budget priority; vehicle under £5,000
Reconditioned Engine	£3,200 – £6,500	£4,200 – £7,800	12–24 months	Most owners — best cost/warranty balance
Rebuilt Engine	£4,500 – £7,500	£5,500 – £9,000	12–24 months	Long-term ownership; 3+ year horizon
Main Dealer New	£6,500 – £9,500	£7,500 – £11,000	24–36 months	Insurance jobs, warranty claims

Figures above reflect the current G22/B48 generation, the most common quote request today. Older generations: see the Era Map above for F32/N20-specific pricing.

Labour estimate: Fitting a 420i engine typically takes 8–12 hours at £75–£110/hr (independent) or £130–£180/hr (London/SE dealer). [PLACEHOLDER — confirm vs cost sheet]

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Common Problems With BMW 4 Series 420i Engines

1. N20 Timing Chain Tensioner & Guide Failure(F32, pre-2016)

Symptoms: Rattling noise on cold start lasting 1–3 seconds, engine warning light, loss of power, metallic noises from the front of the engine, "Drivetrain Malfunction" warning.
Typical Mileage: 60,000–120,000 miles
Repair Cost: £800–£1,800 (preventative chain, tensioner and guide replacement)
Replacement Cost: £3,200–£6,500 (if chain snaps and valves meet pistons)
Urgency: Immediate — if you hear rattle, book an inspection today

Our recommendation:

The N20's timing chain tensioner is the defining weak point of this engine generation. Pre-2016 cars are the highest risk, with the chain guides being prone to failure. BMW revised the tensioner and guides in 2016, but the risk remains on all N20 engines to some degree. A cold-start rattle is the early warning sign — ignore it and you risk piston-valve contact and a full engine replacement. Regular oil changes with the correct BMW-approved oil are the best prevention. At the first sign of rattle, get it inspected immediately.

1. N20 Timing Chain Tensioner & Guide Failure(F32, pre-2016)

Symptoms: Rattling noise on cold start lasting 1–3 seconds, engine warning light, loss of power, metallic noises from the front of the engine, "Drivetrain Malfunction" warning.
Typical Mileage: 60,000–120,000 miles
Repair Cost: £800–£1,800 (preventative chain, tensioner and guide replacement)
Replacement Cost: £3,200–£6,500 (if chain snaps and valves meet pistons)
Urgency: Immediate — if you hear rattle, book an inspection today

Our recommendation:

2. N20 Oil Filter Housing Gasket Failure

Symptoms: Oil leak from the oil filter housing area, oil warning light, low oil pressure, oil on the front of the engine.
Typical Mileage: 40,000–80,000 miles
Repair Cost: £300–£800 (oil filter housing gasket replacement)【PLACEHOLDER】
Replacement Cost: N/A — repair only
Urgency: Monitor — book inspection soon; can lead to oil starvation

Our recommendation:

The N20's oil filter housing gasket is prone to failure, causing oil leaks that can damage other components if left unaddressed. The gasket becomes brittle and cracks over time. A leaking oil filter housing can also lead to oil starvation, which is catastrophic for the engine. Regular inspections can catch this before it becomes a major issue.

3. B48 Coolant Leaks & PCV System Issues(G22)

Symptoms: Low coolant warning, coolant loss with no visible external leak, sweet smell from engine bay, rough idle, white smoke from exhaust (PCV).
Typical Mileage: 40,000–80,000 miles
Repair Cost: £300–£1,200 (coolant system diagnosis and repair, PCV diaphragm repair)
Replacement Cost: N/A — repair only
Urgency: Check — book inspection urgently if coolant loss is detected

Our recommendation:

The B48 is a significant improvement over the N20, but it has its own quirks. Coolant leaks (often from the coolant reservoir, water pump, or charge cooler) are more common than in the N20. The PCV system is also a known weak point, with the valve and diaphragm being prone to failure and causing drivability issues. BMW has released several revised parts for these issues. If you notice coolant loss or rough idle, have the system inspected immediately.

4. Valve Cover Gasket Failure(Both N20 and B48)

Symptoms: Oil leak from the top of the engine, burning oil smell, visible oil seepage around the valve cover.
Typical Mileage: 60,000–100,000 miles
Repair Cost: £400–£900 (valve cover gasket replacement)【PLACEHOLDER】
Replacement Cost: N/A — repair only
Urgency: Monitor — book inspection soon; oil leaks can damage other components

Our recommendation:

Both the N20 and B48 can suffer from valve cover gasket failure. The gasket is made of rubber and has a tendency to become brittle and crack over time due to heat exposure. Obvious oil leaks are the most common symptom. Leaking oil can saturate and degrade vacuum, coolant, and air intake hoses. Regular inspections can catch this before it becomes a major issue.

5. VANOS Solenoid Wear(N20)

Symptoms: Rough idle, hesitation on acceleration, reduced power, check engine light.
Typical Mileage: 70,000–100,000 miles
Repair Cost: £300–£700 (VANOS solenoid replacement)【PLACEHOLDER】
Replacement Cost: N/A — repair only
Urgency: Monitor — book inspection soon; can affect variable valve timing

Our recommendation:

VANOS solenoid failure due to O-ring wear can affect variable valve timing on the N20. If you experience rough idle or hesitation, have the VANOS system inspected promptly.

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420i — Repair, Buy, or Replace?

Not every issue means a new engine.Here’s what can be repaired, when it makes sense, and what to check before you buy.

Can It Be Repaired?

Problem	Repairable?	Typical Cost	When It Makes Sense
N20 timing chain rattle (preventative)	Yes	£800 – £1,800	Catch it early — far cheaper than engine replacement
Oil filter housing gasket (N20)	Yes	£300 – £800	Affordable preventative maintenance
B48 coolant leak	Yes	£300 – £1,200	Diagnosis and repair is straightforward
Valve cover gasket failure	Yes	£400 – £900	Standard maintenance; replace before oil damages other components
VANOS solenoid failure (N20)	Yes	£300 – £700	Replacement is straightforward
Snapped timing chain (N20)	Usually No	Engine replacement	Piston-valve contact means little is left to repair

ProblemRepairable? · Typical Cost

N20 timing chain rattle (preventative)

Yes£800 – £1,800

Catch it early — far cheaper than engine replacement

Oil filter housing gasket (N20)

Yes£300 – £800

Affordable preventative maintenance

B48 coolant leak

Yes£300 – £1,200

Diagnosis and repair is straightforward

Valve cover gasket failure

Yes£400 – £900

Standard maintenance; replace before oil damages other components

VANOS solenoid failure (N20)

Yes£300 – £700

Replacement is straightforward

Snapped timing chain (N20)

Usually NoEngine replacement

Piston-valve contact means little is left to repair

Buying This 420i? Check These First

Buy if:

Full service history with oil changes at 8,000–10,000 mile intervals
N20 cars (pre-2020): timing chain tensioner inspected or replaced (2016+ cars are lower risk)
B48 cars (2020+): no coolant loss and PCV system functioning correctly
No cold-start rattle on N20 cars
B48 cars: no coolant loss or sweet smell from engine bay

Avoid if:

No proof of regular oil changes — these engines are unforgiving of neglect
N20 with cold-start rattle — timing chain work is imminent and expensive
Any coolant loss with no diagnosis — B48 cooling system repairs can be complex
Any engine warning light without diagnosis — the N20 and B48 can hide expensive faults
Excessive oil consumption — indicates potential piston ring or valve seal issues

Closing verdict

The BMW 420i offers a compelling entry into the 4 Series range — sleek styling, strong performance from the 2.0-litre turbo, and excellent fuel economy. The N20-powered F32 generation is a capable car but demands timing chain vigilance, particularly on pre-2016 examples. The B48-powered G22 generation is a significant step forward in reliability and refinement, with the timing chain moved to the front of the engine. Buy on service history, maintain on a shortened schedule, and this is an excellent premium coupé.

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Buying Checklist

Before you buy a used BMW 420i (or before you commit to an engine replacement), check these:

1. Cold Start
Listen for rattle lasting more than 1–2 seconds (N20 timing chain warning)
2. Service History
Including which engine era (N20/B48) and confirmed oil-change discipline (8k–10k miles max)
3. Oil Level
Check dipstick; excessive consumption indicates potential issues
4. Oil Leaks
Check for oil around the oil filter housing (N20) or valve cover (both)
5. Coolant Level
Check cold and hot; any loss indicates B48 cooling system issues
6. Idle Quality
Any roughness? PCV or VANOS issues may be present
7. Engine Warning Light
Have codes been read? Timing, cooling, or VANOS codes are most common
8. MOT History
Check for emissions failures (often related to fuel system or PCV issues)

Why this matters

A 10-minute check now can save you thousands later. The right 4 Series 420i is a superb long-term car — the wrong one can be expensive fast.

Buying Checklist

Before you buy a used BMW 420i (or before you commit to an engine replacement), check these:

1
Cold Start
Listen for rattle lasting more than 1–2 seconds (N20 timing chain warning)
2
Service History
Including which engine era (N20/B48) and confirmed oil-change discipline (8k–10k miles max)
3
Oil Level
Check dipstick; excessive consumption indicates potential issues
4
Oil Leaks
Check for oil around the oil filter housing (N20) or valve cover (both)
5
Coolant Level
Check cold and hot; any loss indicates B48 cooling system issues
6
Idle Quality
Any roughness? PCV or VANOS issues may be present
7
Engine Warning Light
Have codes been read? Timing, cooling, or VANOS codes are most common
8
MOT History
Check for emissions failures (often related to fuel system or PCV issues)

Buy smart. Drive with confidence.

A few checks today can save thousands tomorrow. Use this checklist to avoid the most common 4 Series 420i pitfalls.

Engine Codes

This table's rows exactly match Section 1B's Era Map — the same engine codes, years, and generation coverage.

N20B20 (F32/F33/F36)

Years: 2013–2020
Power: 184 bhp (135 kW) @ 5,000 rpm · 270 Nm @ 1,250–4,500 rpm
2025 Enquiries: —(pattern data)
Avg. Recon Cost: £3,200–£6,500[PLACEHOLDER]

Engine Code	Years	Power	2025 Enquiries	Avg. Recon Cost
N20B20 (F32/F33/F36)	2013–2020	184 bhp (135 kW) @ 5,000 rpm · 270 Nm @ 1,250–4,500 rpm	—(pattern data)	£3,200–£6,500[PLACEHOLDER]
B48B20 (G22/G23/G26)	2020–present	184 bhp (135 kW) @ 5,000 rpm · 300 Nm @ 1,350–4,300 rpm	—(pattern data)	£3,500–£7,500[PLACEHOLDER]

Technical SpecsCurrent B48B20 generation

Displacement: 1,998cc
Cylinders: 4-cylinder inline
Compression Ratio: 11.0:1
Fuel System: Direct injection (Bosch Di-Motronic)
Turbocharger: Single twin-scroll turbocharger with air-to-liquid intercooler
Valvetrain: DOHC with Valvetronic and Double VANOS

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Market Intelligence

Real data from thousands of 4 Series 420i enquiries in 2025.

Most Common FailureN20 timing chain wear

35%

of 420i enquiries cite chain or timing concerns

[PATTERN DATA]

Average Enquiry Mileage

50,000–80,000

miles

[PATTERN DATA]

Average Replacement Cost

£4,800

reconditioned, supply only

[PLACEHOLDER]

Most Requested Engine Code

N20B20

The F32-era 420i is the most common 420i on UK roads

[PATTERN DATA]

Peak Enquiry Season

Winter

Cold starts expose timing chain and cooling issues

[PATTERN DATA]

Regional Demand

South East: 22%
London: 18%
North West: 13%
Other Regions: 47%

[PATTERN DATA]

Regional Demand Breakdown

18%London22%South East13%North West47%Other Regions

Frequently Asked Questions

A reconditioned 420i engine typically costs £3,200–£7,500 supply only depending on generation, with the current B48B20 sitting at £3,500–£7,500. Fitting adds £650–£1,300. Use our calculator for a figure specific to your car.

It depends entirely on which generation you're asking about. The N20 (F32, pre-2020) has a well-documented timing chain tensioner issue — pre-2016 cars are the highest risk. The B48 (G22, 2020+) is significantly more reliable, with the timing chain moved to the front of the engine. Across both, oil-change discipline is everything.

N20 timing chain wear (the defining weak point of the F32 generation), N20 oil filter housing gasket failure, B48 coolant leaks and PCV system issues, and valve cover gasket failure (both engines). See the Era Map above for generation-specific advice.

Depends on vehicle value. Against a well-kept £8,000–£12,000 F32 420i, a £4,000–£4,500 recon is 35–50% of the car's value — often worth it. Against a £20,000+ G22, a £5,000 recon is 25% — worth it. The BMW scrap threshold of 70% means evaluating the whole vehicle and its condition before committing.

Listed on the VIN plate and vehicle documentation. As a rule of thumb: F32/F33/F36 (2013–2020) = N20B20; G22/G23/G26 (2020–present) = B48B20. Tell us your registration date and we'll confirm it for free.

Yes — if caught early. A preventative chain, tensioner and guide replacement costs £800–£1,800. However, if the chain snaps, a full engine replacement (£3,200–£6,500) is usually required. At the first sign of cold-start rattle, book an inspection immediately. Pre-2016 cars are the highest risk — BMW revised the tensioner and guides in 2016.

Disclaimer: All prices are indicative UK market ranges based on historical quote data from our network of engine specialists.
Actual costs vary by variant, engine code, damage severity and workshop location. Use our free comparison tool to get tailored quotes.
Every engine supplied through EnginesMarket carries a minimum 12-month unlimited-mileage warranty — always confirm terms with your chosen supplier.

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BMW 4 Series 420i Engine Replacement —Compare Prices &Get Quotes

The 4 Series 420i Through Time — Era Map

BMW 4 Series 420i Engine Replacement Costs

Common Problems With BMW 4 Series 420i Engines

1. N20 Timing Chain Tensioner & Guide Failure(F32, pre-2016)

2. N20 Oil Filter Housing Gasket Failure

3. B48 Coolant Leaks & PCV System Issues(G22)

4. Valve Cover Gasket Failure(Both N20 and B48)

5. VANOS Solenoid Wear(N20)

1. N20 Timing Chain Tensioner & Guide Failure(F32, pre-2016)

2. N20 Oil Filter Housing Gasket Failure

3. B48 Coolant Leaks & PCV System Issues(G22)

4. Valve Cover Gasket Failure(Both N20 and B48)

5. VANOS Solenoid Wear(N20)

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420i — Repair, Buy, or Replace?

Can It Be Repaired?

Buying This 420i? Check These First

Buying Checklist

Buying Checklist

Engine Codes

Market Intelligence

Regional Demand Breakdown

Frequently Asked Questions

Why UK BMW 4 Series 420i Owners Trust BMWEngines.uk

Trusted 420i Engine Suppliers

Compare 420i Engine Replacement Companies

UK Engine Replacement Services for 420i

BMW 4 Series 420i Engine Replacement —Compare Prices &
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