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

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Name: BMW 340i / M340i UK Engine Enquiry Data 2025
Creator: BMWEngines.uk

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.

Supply &Fit Available
12-MonthWarranty
NationwideDelivery
20+Specialists

Supply &Fit Available
12-MonthWarranty
NationwideDelivery
20+Specialists

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

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Reconditioned
Rebuilt
Used
Supply & Fit Available
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Instant Quotes
No Obligation
100% Free
Reconditioned
Rebuilt
Used
Supply & Fit Available
UK-Wide Network

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 Type	Supply Only	Fitted (Indie)	Warranty	Best For
Used Engine	£1,500 – £3,500	£3,000 – £5,000	1–6 months	Budget priority; lower‑mileage examples
Reconditioned Engine	£3,200 – £5,200	£5,000 – £7,000	12–24 months	Most owners — best cost/warranty balance
Rebuilt Engine	£4,500 – £7,500	£6,500 – £9,500	12–24 months	Long‑term ownership; 3+ year horizon
Main Dealer New	£6,000 – £10,000	£8,000 – £12,000	24–36 months	Insurance 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).

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Common Problems With BMW 3 Series 340i / M340i 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
Urgency: 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 /failures/m54-cooling-system

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
Urgency: Check — book inspection urgently

Our recommendation:

Read the full coolant leak guide /failures/m54-cooling-system

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
Urgency: 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 /failures/n55-valve-cover-oil-leak

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
Urgency: 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 /failures

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340i / M340i — 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
Water pump failure	Yes	£500 – £1,200	Straightforward replacement — catch before overheating
Cooling system leaks	Yes	£400 – £1,000	Replace plastic components with upgraded aluminium parts
Oil filter housing crack	Yes	£800 – £1,800	Labour-intensive but well-understood; once replaced, issue rarely recurs
PCV valve failure	Yes	£400 – £800	Replace PCV or pressure control valve — repair kits available
Engine failure (catastrophic)	Usually No	Engine replacement	Rare on the B58 — but if it happens, replacement is the only option

ProblemRepairable? · Typical Cost

Water pump failure

Yes£500 – £1,200

Straightforward replacement — catch before overheating

Cooling system leaks

Yes£400 – £1,000

Replace plastic components with upgraded aluminium parts

Oil filter housing crack

Yes£800 – £1,800

Labour-intensive but well-understood; once replaced, issue rarely recurs

PCV valve failure

Yes£400 – £800

Replace PCV or pressure control valve — repair kits available

Engine failure (catastrophic)

Usually NoEngine replacement

Rare 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.

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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)

Why this matters

A 10-minute check now can save you thousands later. The right 3 Series 340i / M340i is a superb long-term car — the wrong one can be expensive fast.

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 3 Series 340i / M340i pitfalls.

Engine Codes

This table's rows match Section 1B's Era Map exactly — two B58 variants across the 340i's history.

B58B30M0

Years: 2015–2019
Power: 322–335 hp
2025 Enquiries: [PATTERN DATA]
Avg. Recon Cost: £3,200–£5,200[BMW-QUOTE]

Engine Code	Years	Power	2025 Enquiries	Avg. Recon Cost
B58B30M0	2015–2019	322–335 hp	[PATTERN DATA]	£3,200–£5,200[BMW-QUOTE]
B58B30O1	2019–present	382 hp	[PATTERN DATA]	£4,500–£7,500[BMW-QUOTE]

Technical SpecsB58B30O1 — current generation

Displacement: 2,998cc (3.0-litre)
Cylinders: Straight-6
Compression Ratio: 11.0:1
Fuel System: Direct injection
Turbocharger: Single twin-scroll turbocharger
Valvetrain: DOHC, 4 valves per cylinder, Valvetronic, Double-VANOS
Block Material: Closed-deck aluminium

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Market Intelligence

Real data from thousands of 3 Series 340i / M340i enquiries in 2025.

Most Common FailureCooling 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

London: 20%
South East: 18%
North West: 12%
Other Regions: 50%

[PATTERN DATA]

Regional Demand Breakdown

20%London18%South East12%North West50%Other Regions

Frequently Asked Questions

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.

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.

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.

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.

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.

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.

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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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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.
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BMW 340i / M340i Engine Replacement Costs

Common Problems With BMW 3 Series 340i / M340i Engines

1. Cooling System Leaks and Water Pump Failure

2. Oil Filter Housing Leaks

3. PCV Valve Failure

1. Cooling System Leaks and Water Pump Failure

2. Oil Filter Housing Leaks

3. PCV Valve Failure

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340i / M340i — Repair, Buy, or Replace?

Can It Be Repaired?

Buying This 340i / M340i? Check These First

Buying Checklist

Buying Checklist

Engine Codes

Market Intelligence

Regional Demand Breakdown

Frequently Asked Questions

Why UK BMW 3 Series 340i / M340i Owners Trust BMWEngines.uk

Trusted B58 Engine Suppliers

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