How much does a BMW 340i or M340i engine replacement cost in the UK?

A reconditioned B58 engine typically costs £3,200–£7,500 supply only depending on which generation (F30 or G20), with used units available from £1,500–£3,500. Fitting adds £1,800–£2,500. Use our calculator for a figure specific to your car.

Is the BMW 340i / M340i engine reliable?

Yes - the B58 is widely regarded as one of BMW's most reliable modern engines. It's a significant improvement over the N55 and shares its architecture with the bulletproof B58 used across BMW's range and in the Toyota Supra. The main weaknesses are the cooling system, oil filter housing, and PCV valve - all are well-understood and repairable.

What are the common problems with the BMW 340i and M340i?

Cooling system leaks and water pump failure, oil filter housing cracking (subject to a class action lawsuit), and PCV valve failure causing misfires and rough idle. The B58 is fundamentally robust - these are maintenance items, not catastrophic design flaws.

Is it worth replacing a BMW 340i / M340i engine, or should I scrap the car?

340i and M340i values remain strong - a well-kept G20 M340i is often worth £25,000–£45,000+. A £3,200–£7,500 reconditioned engine is only 10–25% of the vehicle's value - well within the 70% BMW threshold. Replacement is almost always worthwhile.

How do I find my BMW 340i or M340i engine code?

The engine code is listed on the VIN plate and vehicle documentation. F30 340i (2015–2019) uses the B58B30M0; G20 M340i (2019–present) uses the B58B30O1. Tell us your registration date and we'll confirm it for free.

Can I repair the B58 cooling system, or does it need replacement?

Cooling system components need replacement - they are wear items. The water pump (£500–£1,200) and plastic coolant hoses should be replaced preventatively at around 60,000–80,000 miles. Upgraded aluminium parts are available to replace the factory plastic components. Regular coolant level checks are essential - the B58 can lose coolant suddenly.

BMW 3 Series 340i / M340i2015–present3.0-litre Turbo Straight-Six

BMW 340i Engine Replacement — Compare Prices & Get Quotes

The 340i and M340i are powered by BMW's legendary B58 straight-six - one of the most reliable modern turbo engines. The F30-generation B58B30M0 delivers 322–335 hp; the G20 M340i's B58B30O1 produces 382 hp. Get quotes from UK specialists for reconditioned, rebuilt and used units today.

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Supply & Fit Available

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BMW 340i / M340i Engines - from £1,500 to £7,500Common codes: B58B30M0, B58B30O1

BMW 340i / M340i Engines - from £1,500 to £7,500· Common codes: B58B30M0, B58B30O1

Instant QuotesNo Obligation100% FreeReconditionedRebuiltUsedSupply & Fit AvailableUK-Wide Network

The 340i / M340i THROUGH TIME - Era Map

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

GenerationYearsEngine CodeReliabilityRecon CostEra Note

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 340i / M340i Engine Replacement Costs

Supply Only£3,200–£5,200

Fitted (Indie)£5,000–£7,000

Warranty12–24 months

Best ForMost owners - best cost/warranty balance

Engine TypeSupply OnlyFitted (Indie)WarrantyBest For

Used Engine£1,500–£3,500£3,000–£5,0001–6 monthsBudget priority; lower‑mileage examples

Reconditioned Engine£3,200–£5,200£5,000–£7,00012–24 monthsMost owners - best cost/warranty balance

Rebuilt Engine£4,500–£7,500£6,500–£9,50012–24 monthsLong‑term ownership; 3+ year horizon

Main Dealer New£6,000–£10,000£8,000–£12,00024–36 monthsInsurance jobs, warranty claims

Figures above reflect the current 340i/M340i market. F30 B58 engines sit at the lower end; G20 M340i B58TU engines command a premium. See the Era Map above for generation‑specific context.

Labour estimate: Fitting a 340i / M340i engine typically takes 12–16 hours at £65–£95/hr (independent) or £110–£160/hr (London/SE dealer).

→ Compare 340i engine prices from UK specialists

Common Problems With BMW 320d Engines

1. Cooling System Leaks and Water Pump Failure

Symptoms: Coolant loss with no visible external leak, rising temperature gauge, warning light, steam from the engine bay, heater not working properly, limp mode activation

Typical mileage: 60,000–100,000 miles

Repair cost: £500–£1,200 (water pump replacement)

Replacement cost: N/A - repair only

🟠 Check - book inspection urgently

Our recommendation:

The B58's cooling system is its most common weak point. The water pump can fail prematurely - one owner reported the water pump pulley disintegrating during hard acceleration. Coolant loss is frequently reported, with the primary reservoir dropping suddenly. Plastic coolant components (hoses, connectors, thermostat housing) become brittle with age. Upgraded aluminium coolant pipes are available to replace the factory plastic parts. Regular inspection of coolant levels and the water pump is essential - catch it before overheating.

Read the full coolant leak guide

1. Cooling System Leaks and Water Pump Failure

Symptoms: Coolant loss with no visible external leak, rising temperature gauge, warning light, steam from the engine bay, heater not working properly, limp mode activation

Typical mileage: 60,000–100,000 miles

Repair cost: £500–£1,200 (water pump replacement)

Replacement cost: N/A - repair only

🟠 Check - book inspection urgently

Our recommendation:

Read the full coolant leak guide

2. Oil Filter Housing Leaks

Symptoms: Oil spots under the car, burning oil smell from the engine bay, low oil pressure warning, coolant loss, engine warning light

Typical mileage: 60,000–100,000 miles

Repair cost: £800–£1,800 (oil filter housing replacement, including intake manifold removal)

Replacement cost: N/A - repair only

🟠 Check - book inspection urgently

Our recommendation:

The B58's oil filter housing is a known weak point. BMW faces a class action lawsuit over faulty oil filter housings that leak coolant, costing owners thousands in repairs. The housing can crack, causing coolant or oil leaks. Because it sits under the intake manifold, replacement is labour-intensive. Oil leaks from the valve cover gasket are also common. Check for oil spots regularly and investigate any drop in fluid levels promptly. Use high-quality oil filters - poor quality filters can disintegrate and cause housing wear.

Read the full oil filter housing failure guide

3. PCV Valve Failure

Symptoms: Misfires, rough idle, oil in the intake/chargepipe, oil leaks, crankcase pressure issues, check engine light

Typical mileage: 50,000–100,000 miles

Repair cost: £400–£800 (PCV valve or pressure control valve replacement)

Replacement cost: N/A - repair only

🟡 Monitor - book inspection soon

Our recommendation:

One of the most widely discussed B58 problems revolves around faulty crankcase pressure control valves, affecting many BMW models between 2017 and 2021. The PCV (positive crankcase ventilation) valve can fail, causing oil to be drawn into the intake, leading to misfires and rough idle. This issue is especially common on cars with upgraded turbos. Repair kits are available to address the problem without replacing the entire valve cover. Monitor oil consumption and listen for rough idle - if the PCV fails, the engine can run poorly and oil consumption increases.

Read the full PCV valve failure guide

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340i / M340i - 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.

340i / M340i - 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 SenseWater pump failure✅ Yes£500–£1,200Straightforward replacement - catch before overheatingCooling system leaks✅ Yes£400–£1,000Replace plastic components with upgraded aluminium partsOil filter housing crack✅ Yes£800–£1,800Labour-intensive but well-understood; once replaced, issue rarely recursPCV valve failure✅ Yes£400–£800Replace PCV or pressure control valve - repair kits availableEngine failure (catastrophic)❌ Usually NoEngine replacementRare on the B58 - but if it happens, replacement is the only option

Buying This 340i / M340i? Check These First

Buy If

G20 M340i (2019+) - the B58TU brings meaningful improvements over the original F30 version
Documented cooling system maintenance - water pump or hoses replaced at around 60,000–80,000 miles
Full service history with correct BMW-spec oil - the B58 is reliable but unforgiving of neglect
Evidence of oil filter housing inspection or replacement

Avoid If

Evidence of repeated coolant top-ups without a diagnosed leak - the cooling system is the B58's Achilles' heel
Oil spots under the car without a clear diagnosis - likely oil filter housing or valve cover leaks
Poor service history - the B58 is robust but sensitive to oil quality
Any engine warning light without a clear diagnosis

Closing Verdict

The B58 is one of BMW's finest modern engines - a genuine step forward in reliability from the N55 that preceded it. It's smooth, torquey, and durable. Its weaknesses are well-understood: the cooling system, oil filter housing, and PCV valve. Buy on history, maintain on schedule, and the B58 will reward you with exceptional performance and longevity. The G20 M340i's B58TU represents the most refined version of this engine.

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

→ Compare 340i engine prices before you buy

Don't Guess. Compare.

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

→ Compare 340i engine prices before you buy

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Buying Checklist

Before you buy a used BMW 340i or M340i (or before you commit to an engine replacement), check these:

1. Coolant Level

Any unexplained loss? (cooling system warning - check the primary reservoir)

2. Service History

including which generation (F30 or G20) and evidence of cooling system maintenance

3. Oil Spots

Any oil under the car? (oil filter housing or valve cover leak warning)

4. Cold Start

Any rattles? (timing chain issues are rare on B58 but possible)

5. Idle Quality

Any rough idle or misfires? (PCV or injector issues)

6. Engine Warning Light

Have codes been read? Any unresolved issues?

7. Turbo Performance

Test acceleration; any hesitation, whistling, or wastegate rattle?

8. MOT History

Check for emissions-related failures (catalyst, O2 sensors)

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 - two B58 variants across the 340i's history.

B58B30M0

Years2015–2019

Power322–335 hp

2025 Enquiries[PATTERN DATA]

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

Engine CodeYearsPower2025 EnquiriesAvg. Recon Cost

B58B30M02015–2019322–335 hp[PATTERN DATA]£3,200–£5,200 [BMW-QUOTE]

B58B30O12019–present382 hp[PATTERN DATA]£4,500–£7,500 [BMW-QUOTE]

Technical Specs

B58B30O1 - current generation

Displacement2,998cc (3.0-litre)

CylindersStraight-6

Compression Ratio11.0:1

Fuel SystemDirect injection

TurbochargerSingle twin-scroll turbocharger

ValvetrainDOHC, 4 valves per cylinder, Valvetronic, Double-VANOS

Block MaterialClosed-deck aluminium

→ Compare 340i engine prices for your BMW

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Market Intelligence

Most Common Failure

Cooling system leaks and water pump failure

the primary weakness of the B58

Average Enquiry Mileage

50,000

–80,000 miles【PATTERN DATA】

Average Replacement Cost

£3,200

–£7,500 reconditioned, supply only depending on generation【BMW-QUOTE】

Most Requested Engine Code

B58

one of BMW's most celebrated modern engines【PATTERN DATA】

Peak Enquiry Season

Spring

pre‑summer vehicle preparation【PATTERN DATA】

Regional Demand

London20%

South East18%

North West (12%)【PATTERN DATA】

Regional Demand Breakdown

20%London

18%South East

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.

Trusted B58 Engine Suppliers
every garage and engine rebuilder in our network is vetted, rated and reviewed by real 340i and M340i owners, as part of the Engine Finders network, across both the F30 and G20 generations - no matter which B58 era your 3 Series belongs to.
Compare 340i / M340i Engine Replacement Companies
see prices, warranty terms and supply & fit options side‑by‑side before you commit, with specialists who genuinely understand the B58's cooling system, oil filter housing, and PCV valve nuances.
UK Engine Replacement Services for 340i / M340i
supply‑only or full supply & fit available nationwide, covering BMW's legendary B58 straight-six with a 12‑month warranty as standard.

Find the best BMW 340i or M340i engine replacement UK drivers rely on. Compare prices from trusted specialists on EnginesMarket today and keep your B58-powered 3 Series performing at its best.

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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