How much does a BMW 4 Series 425d engine replacement cost in the UK?

A reconditioned 425d engine (N47S1 or B47D20B) typically costs £2,000–£4,200 supply only depending on engine generation. Fitting adds £1,000–£1,500. Use our calculator for a figure specific to your vehicle.

Is the BMW 4 Series 425d engine reliable?

It depends on which engine generation your 425d has. The N47S1 (pre‑LCI, 2014–2017) is a punchy twin‑turbo diesel but has a well‑documented weakness: timing chain failure. The B47D20B (LCI, 2017–2020) is the successor engine that addressed these timing chain issues and offers 224 bhp. Both engines demand strict maintenance – regular oil changes (8,000–10,000 miles) are essential.

What are the common problems with the BMW 4 Series 425d?

On the pre‑LCI N47S1, the most serious issue is timing chain failure – the chain, guides, and tensioners can wear prematurely, causing chain stretch and potential catastrophic engine damage. On both N47S1 and B47D20B, common problems include EGR valve/cooler failure, DPF blockage from urban driving, and oil leaks (valve cover, oil filter housing).

Is it worth replacing a 425d engine, or should I scrap the car?

Depends on vehicle value and condition. Against a tidy £5,000–£15,000 4 Series, a £2,000–£4,200 recon is 15–45% of the car's value – often worth it on well‑maintained examples. If the timing chain has snapped on an N47S1 and caused valve damage, a full engine replacement may be necessary. Get a full diagnostic assessment before committing.

How do I find my 4 Series's engine code?

The pre‑LCI F32/F33/F36 (2014–2017) uses the N47S1 (N47D20T1) – check for the rear‑mounted timing chain design. The LCI (2017–2020) uses the B47D20B – the improved successor engine. The engine code is stamped on the engine block and listed on your V5C.

Can I repair a 425d engine issue, or does it need replacement?

Most issues – timing chain wear (if caught early on N47S1), EGR valve failure, DPF blockage, oil leaks – are repairable. However, if the timing chain has snapped on an N47S1, the engine is an interference design – pistons will strike valves. In this case, a full engine replacement is usually more cost‑effective than a rebuild.

BMW 4 Series 425d2014–20202.0L Twin‑Turbo Diesel (N47S1 / B47D20B)

BMW 4 Series 425d Engine Replacement — Compare Prices & Get Quotes

Name: BMW 4 Series 425d UK Engine Enquiry Data 2025
Creator: BMWEngines.uk

Get quotes today from trusted UK BMW specialists. Compare reconditioned, rebuilt and used N47S1 and B47D20B 2.0‑litre twin‑turbo diesel engines for the 4 Series 425d - the punchy, efficient diesel six‑cylinder alternative. Supply & fit available nationwide.

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BMW 4 Series 425d Engines - from £1,200 to £4,200Common codes: N47D20T1 (N47S1), B47D20B

BMW 4 Series 425d Engines - from £1,200 to £4,200· Common codes: N47D20T1 (N47S1), B47D20B

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BMW 4 Series 425d - Which Engine Does Your Car Actually Have?

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

Era Note

218 bhp - twin‑turbo version of the N47, timing chain is the defining weakness

GenerationYearsEngine CodeReliabilityRecon CostEra Note

F32/F33/F36 (Pre‑LCI) BMW 320d F32/F33/F36 (Pre‑LCI)

2014–2017N47S1 (N47D20T1, 2.0L Twin‑Turbo I4)★★★½☆ [NEWLY ASSIGNED - see Data Note]£2,000–£3,500 [PLACEHOLDER - confirm vs cost sheet]218 bhp - twin‑turbo version of the N47, timing chain is the defining weakness

F32/F33/F36 (LCI) BMW 320d F32/F33/F36 (LCI)

2017–2020B47D20B (2.0L Twin‑Turbo I4)★★★★☆ [NEWLY ASSIGNED - see Data Note]£2,200–£4,200 [PLACEHOLDER - confirm vs cost sheet]224 bhp - updated twin‑turbo, timing chain reliability significantly improved

Why use this era map?

This table is the single source every other section on this page must match. Sections 2, 4, and 6 reference it rather than restating conflicting figures.

Real UK Cost Data

Verified Reliability

Expert Insights

Updated for 2025

BMW 4 Series 425d Engine Replacement Costs

Supply Only£2,000–£3,500

Fitted (Indie)£3,000–£4,800

Warranty12–24 months

Best ForMost owners - best cost/warranty balance

Engine TypeSupply OnlyFitted (Indie)WarrantyBest For

Used Engine£1,200–£2,200£1,800–£3,2001–6 monthsBudget priority; short‑term ownership

Reconditioned Engine£2,000–£3,500£3,000–£4,80012–24 monthsMost owners - best cost/warranty balance

Rebuilt Engine£3,000–£4,200£4,000–£5,50012–24 monthsLong‑term ownership; maximum reliability

Main Dealer New£5,000–£6,500£6,500–£8,00024–36 monthsInsurance jobs; warranty claims; full provenance

Figures above reflect the 425d pricing across generations. The N47S1 and B47D20B have broadly similar replacement costs, though B47 engines (being newer) may command a slight premium. Older generations: see the Era Map above for generation-specific pricing.

Labour estimate: Fitting a 425d engine typically takes 8–12 hours at £75–£110/hr (independent BMW specialist).

→ Compare 4 Series 425d engine prices from UK specialists

Common Problems With BMW 320d Engines

1. Timing Chain Failure - N47S1 (Pre‑LCI, 2014–2017)

Symptoms: Cold‑start rattle lasting 1‑3 seconds, metallic ticking from the engine, rattling persisting when warm, engine warning light, loss of power - catastrophic failure can occur without warning.

Typical mileage: 60,000–100,000 miles (rear‑mounted chain design is labour‑intensive to access).

Repair cost: £1,200–£2,500 [PLACEHOLDER] (timing chain, tensioner, and guide replacement - engine or gearbox removal required).

Replacement cost: £2,000–£4,200 [PLACEHOLDER] (if chain snaps and damages the engine).

🔴 Immediate - if you hear cold‑start rattle, book an inspection immediately.

Our recommendation:

The N47 timing chain is the defining weakness of this engine generation. The chain is mounted at the rear of the engine, against the firewall, making access labour‑intensive. The chain, guides, and tensioners can wear prematurely, causing chain stretch. If the chain stretches too far, it can "jump" a tooth or snap, causing pistons to strike valves in this interference engine. A £1,200–£2,500 preventative chain replacement is far cheaper than a £2,000–£4,200 engine replacement. At the first sign of cold‑start rattle, have the timing system inspected immediately. The B47 (2017‑onwards) addressed these issues with an improved timing chain design.

1. Timing Chain Failure - N47S1 (Pre‑LCI, 2014–2017)

Typical mileage: 60,000–100,000 miles (rear‑mounted chain design is labour‑intensive to access).

Repair cost: £1,200–£2,500 [PLACEHOLDER] (timing chain, tensioner, and guide replacement - engine or gearbox removal required).

Replacement cost: £2,000–£4,200 [PLACEHOLDER] (if chain snaps and damages the engine).

🔴 Immediate - if you hear cold‑start rattle, book an inspection immediately.

Our recommendation:

2. EGR Valve / Cooler Failure (N47S1 & B47D20B)

Symptoms: Reduced power, rough idle, engine warning light, increased fuel consumption, black smoke from exhaust, failed emissions test.

Typical mileage: 40,000–80,000 miles.

Repair cost: £400–£1,000 [PLACEHOLDER] (EGR valve or cooler replacement).

Replacement cost: N/A - repair only (if caught early).

🟠 Check - book inspection urgently if engine warning light appears.

Our recommendation:

EGR system failure is a common issue on both N47 and B47 diesel engines. The EGR valve can become clogged with soot, and the EGR cooler can develop leaks, leading to coolant loss. Some N47 engines were subject to a recall for EGR cooler leaks. Regular motorway driving and using high‑quality diesel can help reduce EGR clogging. If the engine warning light appears with EGR‑related codes, have the system diagnosed promptly.

3. DPF Blockage (Urban Driving)

Symptoms: Reduced power, increased fuel consumption, engine warning light, DPF warning message, failed emissions test, oil level rising (fuel dilution).

Typical mileage: 30,000–80,000 miles (depends on driving patterns).

Repair cost: £400–£1,200 [PLACEHOLDER] (DPF cleaning or replacement).

Replacement cost: N/A - repair only (if caught early).

🟡 Monitor - book inspection soon if DPF warning appears.

Our recommendation:

The 425d's twin‑turbo diesel is sensitive to driving patterns. If used primarily for short urban trips, the Diesel Particulate Filter (DPF) will clog. Regular motorway runs (30+ minutes at 60+ mph) are essential to maintain the exhaust filtration system. Oil changes every 8,000–10,000 miles are recommended rather than BMW's suggested longer intervals to prolong engine and DPF life.

4. Oil Leaks - Valve Cover & Oil Filter Housing (N47S1 & B47D20B)

Symptoms: Oil spots under the vehicle, burning oil smell, low oil level warning, visible oil leak from the top or front of the engine.

Typical mileage: 40,000–80,000 miles.

Repair cost: £300–£800 [PLACEHOLDER] (valve cover gasket or oil filter housing gasket replacement).

Replacement cost: N/A - repair only (if caught early; ignored oil loss can lead to engine damage).

🟠 Check - book inspection urgently if oil leak is detected.

Our recommendation:

Both N47 and B47 engines are known for oil leaks from the valve cover gasket and oil filter housing gasket. If the oil filter housing gasket fails, oil can leak onto the serpentine belt, causing it to slip or break - which can then be ingested into the engine through the front crankshaft seal, causing catastrophic failure. If you notice oil spots under your 425d or a burning oil smell, investigate immediately. A £300–£800 gasket replacement is far cheaper than the consequences of a snapped belt.

Weighing Your Options?

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BMW 4 Series 425d - 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 4 Series 425d - 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 SenseTiming chain wear - N47S1✅ Yes (if caught early)£1,200–£2,500 [PLACEHOLDER]Catch it early - cheaper than engine replacementTiming chain snapped - N47S1❌ Usually No£2,000–£4,200+Full engine replacement - valve damage is almost certainEGR valve / cooler failure✅ Yes£400–£1,000 [PLACEHOLDER]Worth fixing - common and well‑understood repairDPF blockage✅ Yes£400–£1,200 [PLACEHOLDER]Routine maintenance - always worth doingOil leaks (valve cover / OFHG)✅ Yes£300–£800 [PLACEHOLDER]Essential maintenance - always worth doingMajor internal failure (crank, bearings)❌ Usually No£2,000–£4,200+Full engine replacement often more cost‑effective

Buying This BMW 4 Series 425d? Check These First

Buy If

Full BMW service history with documented oil changes (every 8,000–10,000 miles)
Pre‑LCI (N47S1): Timing chain inspected and any work documented
LCI (B47D20B): Evidence of regular motorway driving (DPF‑friendly usage)
A well‑maintained example with lower mileage

Avoid If

Pre‑LCI (N47S1): Any sign of cold‑start rattle - this is the defining weakness
No evidence of regular oil changes - both engines are intolerant of neglect
DPF warnings on the dashboard - indicates urban‑only driving
Poor service history - these engines demand strict maintenance

Closing Verdict

The BMW 425d offers punchy twin‑turbo diesel performance in a stylish coupe, convertible, or Gran Coupe body. The pre‑LCI N47S1 is a capable engine with a well‑documented Achilles heel: timing chain failure. The LCI B47D20B addresses this with an improved design and delivers 224 bhp. Buy on service history above all else - a vehicle with documented timing chain maintenance and regular oil changes is a safe bet; a neglected example can be expensive to repair.

Don't guess.Get the right engine at the right price.

→ Compare 4 Series 425d engine prices before you buy

Don't Guess. Compare.

Get real quotes from vetted UK specialists and make the right call for your 320d.

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Buying Checklist

Before you buy a used BMW 4 Series 425d (or before you commit to an engine replacement), check these:

1. Cold Start

Any rattle for 1‑3 seconds? (timing chain warning on N47S1 - stop immediately)

2. Service History

Regular oil changes (8,000–10,000 miles) - this is non‑negotiable

3. Timing Chain History

N47S1: Has the chain been inspected or replaced?

4. DPF Health

Has the vehicle done regular longer runs? (short trips kill DPFs)

5. EGR System

Any engine warning lights? Any EGR‑related codes?

6. Oil Leaks

Check under the vehicle and around the valve cover and oil filter housing

7. Oil Consumption

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

8. MOT History

Check for emissions‑related failures or any advisory notes

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

This table's rows match Section 1B's Era Map exactly.

N47S1 (N47D20T1, 2.0L Twin‑Turbo I4)

Years2014–2017

Power218 bhp (160 kW) / 450 Nm

2025 Enquiries- (pattern data)

Avg. Recon Cost£2,000–£3,500 [PLACEHOLDER]

Engine CodeYearsPower2025 EnquiriesAvg. Recon Cost

N47S1 (N47D20T1, 2.0L Twin‑Turbo I4)2014–2017218 bhp (160 kW) / 450 Nm- (pattern data)£2,000–£3,500 [PLACEHOLDER]

B47D20B (2.0L Twin‑Turbo I4)2017–2020224 bhp (165 kW) / 450 Nm- (pattern data)£2,200–£4,200 [PLACEHOLDER]

Technical Specs

N47S1 / B47D20B - 2.0L Twin‑Turbo Diesel

Displacement1,995 cc

Cylinders4‑cylinder inline

Compression Ratio16.5:1

Fuel SystemCommon‑rail direct injection

AspirationTwin‑turbocharged (sequential)

→ Compare 4 Series 425d engine prices for your BMW

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Market Intelligence

Most Common Failure

N47S1: Timing chain failure

the defining weakness of the pre‑LCI 425d

Average Enquiry Mileage

50,000

–80,000 miles

[PATTERN DATA]

Average Replacement Cost

£2,500

reconditioned, supply only

[PLACEHOLDER]

Most Requested Engine Code

N47S1

the pre‑LCI engine is more common on the used market

[PATTERN DATA]

Peak Enquiry Season

Autumn/Winter

cold starts expose timing chain wear

[PATTERN DATA]

Regional Demand

South East20%

London14%

North West (12%) - premium coupe strongholds

PATTERN DATA

Regional Demand Breakdown

20%South East

14%London

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.

Why UK BMW 4 Series 425d Owners Trust BMWEngines.uk

Trusted 425d Engine Suppliers
every garage and engine rebuilder in our network is vetted, rated and reviewed by real 4 Series owners, as part of the Engine Finders network, covering both the N47S1 twin-turbo diesel and its B47D20B successor, with specialist knowledge of BMW's twin-turbo diesel technology.
Compare 425d Engine Replacement Companies
see prices, warranty terms and supply & fit options side‑by‑side before you commit, with specialists who understand the N47's timing chain vulnerabilities, the B47's improved reliability, and the importance of regular oil changes and DPF maintenance.
UK Engine Replacement Services for the 4 Series
supply‑only or full supply & fit available nationwide, covering every generation of this badge from the pre‑LCI F32 through to the LCI F32/F33/F36, with specialist knowledge of BMW's twin‑turbo diesel engines.

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12-Month Warranty

As standard

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