How much does a BMW 420d engine replacement cost in the UK?

A reconditioned 420d engine typically costs £3,200–£5,500 supply only depending on generation, with the B47 currently sitting at £3,400–£6,200. Fitting adds £1,000–£1,500. Use our calculator for a figure specific to your car.

Is the BMW 420d engine reliable?

It depends on the generation. Pre-2017 cars with the N47 have the well-documented rear-chain risk (★★★☆☆). 2017+ cars with the B47 have the chain relocated to the front (★★★★☆), eliminating the specific N47 failure mode. The B47 is considered meaningfully more reliable.

What are the common problems with the BMW 420d?

Timing chain wear on N47-engined cars (pre-2017), B47 timing chain tensioner wear (2017+), and an EGR cooler coolant leak affecting both engines. The B47 is significantly more reliable than the N47.

Is it worth replacing a BMW 420d engine, or should I scrap the car?

Depends on vehicle value. Against a well-kept £8,000 420d, a £4,200 recon is 52% of the car's value - assess carefully. For a 2017+ B47 car worth £12,000+, the same recon is 35% - more justifiable. Always assess the rest of the car before committing.

How do I find my BMW 420d engine code?

Listed on the VIN plate and vehicle documentation. As a rule of thumb: 2013–2017 is N47, 2017-onward is B47. Tell us your registration date and we'll confirm it for free.

Can I repair the N47 timing chain, or does it need replacement?

Yes - if caught early. A preventative chain replacement (£650–£1,800) is far cheaper than a catastrophic chain snap (£3,200–£5,500 engine replacement). At the first sign of cold-start rattle, book an inspection immediately.

BMW 4 Series 420d2013–present2 Generations

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

Get quotes today from trusted UK BMW 420d specialists. Compare reconditioned, rebuilt and used N47 and B47 engines for Coupé, Convertible and Gran Coupé - supply & fit available nationwide.

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BMW 420d Engines - from £1,800 to £6,500Common codes: N47D20C, B47D20

BMW 420d Engines - from £1,800 to £6,500· Common codes: N47D20C, B47D20

Instant QuotesNo Obligation100% FreeReconditionedRebuiltUsedSupply & Fit AvailableUK-Wide Network

The 420d THROUGH TIME - Era Map

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

Era Note

The 420d's defining engine - N47 rear-chain risk applies to 2013–2017 examples.

GenerationYearsEngine CodeReliabilityRecon CostEra Note

F32 / F33 / F36 BMW 320d F32 / F33 / F36

2013–2017N47D20C★★★☆☆ [BMW-VERIFIED - inherited from Model Page & E90 Generation Page]£3,200–£5,500 [BMW-QUOTE]The 420d's defining engine - N47 rear-chain risk applies to 2013–2017 examples.

F32 / F33 / F36 BMW 320d F32 / F33 / F36

2017–2020B47D20★★★★☆ [NEWLY ASSIGNED - see Data Note]£3,400–£5,800 [PLACEHOLDER]2017 facelift brought the B47 - chain relocated to the front, a genuinely different risk profile.

G22 / G23 / G26 BMW 320d G22 / G23 / G26

2020–presentB47D20 (MHEV on some)★★★★☆ [NEWLY ASSIGNED - see Data Note]£3,600–£6,200 [PLACEHOLDER]The modern generation - B47 with 48V mild-hybrid on later examples; the most refined 420d yet.

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 UK Cost Data

Verified Reliability

Expert Insights

Updated for 2025

BMW 4 Series 420d Engine Replacement Costs

Supply Only£3,200–£5,500

Fitted (Indie)£4,200–£6,800

Warranty12–24 months

Best ForMost owners - best cost/warranty balance

Engine TypeSupply OnlyFitted (Indie)WarrantyBest For

Used Engine£1,800–£3,000£2,650–£4,0001–6 monthsBudget priority; vehicle under £5,000

Reconditioned Engine£3,200–£5,500£4,200–£6,80012–24 monthsMost owners - best cost/warranty balance

Rebuilt Engine£4,500–£6,500£5,500–£7,80012–24 monthsLong-term ownership; 3+ year horizon

Main Dealer New£8,000–£12,000£9,500–£14,00024–36 monthsInsurance jobs, warranty claims

Labour estimate: Fitting a 420d engine typically takes 10–14 hours at £65–£95/hr (independent) or £110–£160/hr (London/SE dealer).

Common Problems With BMW 320d Engines

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BMW 420d - Repair, Buy, or Replace?

Every 320d has a story. Make the right call with clear data, real-world costs, and honest guidance from UK specialists.

BMW 420d - Repair, Buy, or Replace?

Every 320d has a story. Make the right call with clear data, real-world costs, and honest guidance from UK specialists.

Can It Be Repaired?

ProblemRepairable?Typical CostWhen It Makes SenseCold-start timing chain rattle (N47)✅ Yes£650–£1,800Preventative - catches the fault before it becomes catastrophicEGR cooler coolant leak (N47/B47)✅ Yes£300–£600Straightforward fix if caught before overheatingB47 timing chain tensioner wear✅ Yes£1,200–£2,500If caught early - far cheaper than a new engineSnapped timing chain (N47)❌ Usually NoEngine replacementPiston-valve contact means little is left to repairDPF clogging (both engines)✅ Yes£400–£1,200Preventative - regular motorway runs are the best prevention

Buying This 420d? Check These First

Buy If

2017+ B47 if you want to avoid the N47 chain risk entirely
Documented timing-chain history if buying a pre-2017 N47
Confirmed EGR recall completion on any 420d
Full service history with sub-15,000km oil intervals

Avoid If

Pre-2017 N47 with cold-start rattle and no chain history
EGR recall not completed on any 420d
Poor service history on any generation
Engine warning light with no diagnosis, regardless of generation

Closing Verdict

The 420d is the core 4 Series diesel - and the engine choice determines your ownership experience. 2017+ B47 cars are meaningfully more reliable than the earlier N47. Buy on documented history, and if you're looking at a pre-2017 car, demand chain-history proof before you commit.

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Buying Checklist

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

Cold Start

Listen for 1–30 seconds of rattle (timing chain warning on N47)

Service History

Including which engine era (N47 for pre-2017, B47 for 2017+) - see the Era Map above

Smoke Check

White smoke on startup can indicate EGR coolant leak

Turbo Boost

Test acceleration; any lag, whistling, or grinding?

DPF Regeneration

Check history; short journeys accelerate wear on all diesel eras

Oil Consumption

Does it use more than 1L per 1,000 miles?

Engine Warning Light

Have codes been read? Any unresolved issues?

MOT History

Check for emissions-related failures

Buy smart. Drive with confidence.

A few checks today can save thousands tomorrow. Use this checklist to avoid the most common 320d pitfalls.

Buy smart. Drive with confidence.

A few checks today can save thousands tomorrow. Use this checklist to avoid the most common 320d pitfalls.

BMW 320d Engine Codes

N47D20C

Years2013–2017

Power184 bhp / 380 Nm

2025 Enquiries1,450 JLR-wide [BMW-VERIFIED]

Avg. Recon Cost£3,200–£5,500 [BMW-QUOTE]

Engine CodeYearsPower2025 EnquiriesAvg. Recon Cost

N47D20C2013–2017184 bhp / 380 Nm1,450 JLR-wide [BMW-VERIFIED]£3,200–£5,500 [BMW-QUOTE]

B47D202017–present190 bhp / 400 Nm- (pattern data)£3,400–£6,200 [PLACEHOLDER]

Technical Specs

current B47D20 generation

Displacement1,995cc

Cylinders4-cylinder inline

Compression Ratio16.5:1

Fuel SystemCommon-rail direct injection

TurbochargerSingle-turbo (VGT)

Market Intelligence

Most Common Failure

N47 rear timing chain

60%

of pre-2017 420d enquiries

[PATTERN DATA]

Average Enquiry Mileage

75,000

miles

[PATTERN DATA]

Average Replacement Cost

£4,200

reconditioned, supply only

[BMW-QUOTE]

Most Requested Engine Code

N47D20C

[BMW-VERIFIED]

Peak Enquiry Season

Winter

cold starts expose chain issues

[PATTERN DATA]

Regional Demand

London22%

South East18%

North West12%

PATTERN DATA

Regional Demand Breakdown

22%London

18%South East

12%North West

BMW 320d - Frequently Asked Questions

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.

Find the best BMW 420d engine replacement UK drivers rely on. Compare prices from trusted specialists on EnginesMarket today and get back on the road with confidence.

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100% Free

No hidden fees

No Obligation

Get quotes with zero pressure

UK Specialists

20+ vetted experts

12-Month Warranty

As standard

Nationwide Delivery

Supply & fit available