How much does a Mercedes E Class 450 engine replacement cost in the UK-

Supply-only rebuilt M256 engines range from £5,500 to £8,500 depending on condition. With specialist fitting, budget £6,000-£9,300 total. M274.920 (E 300, 245 hp, 2016-2021): rebuilt £3,800-£5,500. M256.930 (E 450, 367 hp with EQ Boost, 2018-present): rebuilt £5,500-£8,500. Labour adds £500-£1,000 depending on specialist location - the M256's rear-mounted timing chain makes it a more complex job.

What are the signs of M274 piston failure in an E Class 300-

There are often no warning signs - the M274's piston cracking from LSPI is sudden and catastrophic. Some owners report a knocking noise or loss of power immediately before failure. Loss of power or engine misfire. Knocking noise from the engine. Check engine light with misfire codes. There is no preventative fix - rebuilt engines with forged pistons are the only permanent solution.

Is it worth replacing the engine on an E Class 300 or 450-

Yes, if the car is otherwise sound. W213 E 300 examples command £10,000-£22,000 used, while E 450 examples command £20,000-£40,000, making replacement viable. A quality rebuilt M274 costs £3,800-£5,500 supply only. A quality rebuilt M256 costs £5,500-£8,500 supply only. The M256 is Mercedes' most advanced straight-six petrol engine. A replacement engine with warranty costs less than the depreciation on a newer car.

What causes the M256 timing chain to fail on E 450 models-

The M256's timing chain tensioners and guides can wear prematurely, causing cold-start rattling - described as 'marbles in a can'. M256 engines can show timing component wear after 120,000 km. Timing chain rattle typically occurs between 40,000-75,000 miles. Cold-start rattling that disappears after a few seconds is the early warning. The timing chain is located at the rear of the engine - replacement is an engine-out job. Full timing chain replacement at a specialist costs £2,200-£3,500.

What is the difference between the M274 and M256 engines in the E Class-

The M274 is a 2.0-litre turbocharged four-cylinder (E 300, 245 hp) with known piston cracking issues. The M256 is a 3.0-litre turbocharged straight-six (E 450, 367 hp) with EQ Boost mild-hybrid technology - more powerful, smoother, and generally more reliable. M274: 2.0L four-cylinder, 245 hp, 370 Nm - prone to piston cracking, timing chain stretch, and thermostat failure. M256: 3.0L straight-six, 367 hp + 22 hp EQ Boost, 500 Nm - features 48-volt mild-hybrid system, electric auxiliary compressor, and integrated starter-generator. The M256 replaced the M276 V6 and is Mercedes' first petrol straight-six since the M104. The M256 is generally more reliable but more expensive to repair due to complexity.

How long does a Mercedes E Class 450 engine last-

With proper maintenance and 8,000-10,000 mile oil changes, M256 engines regularly reach 150,000-200,000+ miles. The M256 is a modern, efficient design with a robust bottom end. M256 straight-six is a modular design sharing architecture with four-cylinder and V8 engines. Timing chain inspection/replacement at 40k-75k miles is recommended if rattle occurs. Regular oil changes (8,000 miles) are critical for timing chain life. The M256 is generally considered more reliable than the M274.

Mercedes E Class 300 / 450 Petrol SPECIALISTS

Mercedes Benz E Class 300 / 450 Modern Petrol Engine Replacement Compare Prices & Get Quotes

Get quotes today from trusted UK Mercedes Benz E Class 300 and 450 petrol engine specialists. Compare prices on reconditioned, rebuilt and used M274 and M256 engines - including EQ Boost mild-hybrid variants - supply & fit available nationwide.

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Mercedes Benz E Class 300 / 450 Modern Petrol Engine

from£3,200 to £8,500

Usedfrom £2,000
Reconditionedfrom £3,500
Common codesM274.920, M256.930

Mercedes Benz e-class 300 / 450 Modern Petrol Used Engine — M274.920

Mercedes Benz e-classUsed Engine — M274.920

Mercedes Benz e-class 300 / 450 Modern Petrol Reconditioned Engine — M274.920

Mercedes Benz e-classReconditioned Engine — M274.920

Mercedes Benz e-class 300 / 450 Modern Petrol Rebuilt Engine — M274.920

Mercedes Benz e-classRebuilt Engine — M274.920

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How it works

3 Simple Steps to Finding the Right Replacement Engine

Clear information first, then the right engine and specialist for your exact vehicle.

Variant History

Mercedes Benz E Class 300 / 450 Modern Petrol Engine History & Specs at a Glance

The E 300 and E 450 petrol badges represent Mercedes-Benz's premium petrol offerings across the W213 and W214 E-Class generations. The E 300 uses the M274 2.0-litre turbocharged four-cylinder - a proven but troubled unit - while the E 450 is powered by the M256 3.0-litre turbocharged straight-six, Mercedes' first petrol inline-six since the M104. The M256 introduced EQ Boost mild-hybrid technology, featuring a 48-volt electrical system with an integrated starter-generator (ISG) that adds up to 16 kW (22 hp) and 220 Nm of torque assistance. The M256 is also equipped with an electric auxiliary compressor (BorgWarner eBooster) that spins at up to 70,000 rpm to virtually eliminate turbo lag. The modular engine family shares a 500 cc per cylinder architecture with Mercedes' four-cylinder and V8 engines.

2016
W213 E 300 launched with M274.920 2.0-litre turbo four-cylinder, 180 kW (245 hp), 370 Nm
2017
M256 engine introduced on W222 S-Class, later adopted by E-Class range
2018
E 450 launched with M256.930 3.0-litre straight-six, 270 kW (367 hp), 500 Nm, featuring EQ Boost mild-hybrid system
**2018-2020** - E 400 (pre-facelift) offered with M276 V6 in some markets, superseded by E 450
2020
W213 facelift; E 300 continues with M274, E 450 gains updated M256.930 with enhanced mild-hybrid system
2020
E 450 EQ Boost 4MATIC introduced with 367 hp and 500 Nm
2023
W214 generation launched; E 300 and E 450 continue with updated M256/M254 engine architecture

Every engine fitted to the Mercedes E Class 300 and 450 modern petrol is covered below, with UK rebuilt pricing and known failure points.

Engine Codes & Pricing

Mercedes Benz E Class 300 / 450 Modern Petrol Engine Codes Specifications & Replacement Cost

Find your exact engine code, specs and UK replacement cost guide.

M274.920 — 2.0L Turbo Petrol (2016-2021)

Power Output: 180 kW (245 hp) at 5,500 rpm
Torque: 370 Nm at 1,300-4,000 rpm
Years Fitted: 2016-2021 (W213 E-Class)

Can’t find your exact engine code?-> Get quotes for M274 Mercedes E Class 300 petrol engine replacement

-> Get quotes for M274 Mercedes E Class 300 petrol engine replacement

Common Problems

Mercedes E Class 300 / 450 Modern Petrol Engine Problems Repair Cost vs Replacement

The E Class 300 and 450 represent the pinnacle of Mercedes petrol engineering in the modern era. The M274 four-cylinder in the E 300 is a powerful unit but carries a catastrophic reputation for piston cracking - a failure with no preventative fix. The M256 straight-six in the E 450 is a technological marvel - Mercedes' first petrol inline-six since the M104 - featuring EQ Boost mild-hybrid technology, but it introduces its own set of complex issues around timing chain wear and 48-volt system reliability. Every rebuilt engine supplied through EnginesMarket includes upgraded components designed to address the original failure point, plus a minimum 12-month unlimited mileage warranty. Below, we break down what these failures cost to fix and when replacement is the smarter option.

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Common failure points and repair options

M274 Piston Cracking

Affected: Mercedes E Class 300 (M274.920, 2016-2021)
Typical failure mileage: 30,000 - 90,000 miles (some as early as 40,000 miles)

Root cause

Low-speed pre-ignition (LSPI) combined with oil dilution causes detonation events that crack pistons between ring lands. There is no preventative fix - once a piston cracks, the engine must be rebuilt or replaced. The M274 piston failure is so well-documented that some owners have been advised to "dump the E300" rather than repair it, as a repaired engine remains as prone to cracking as the original.

Repair options

Repair tier	Dealer price	Specialist price
Major - Short Block Replacement	£5,000-£7,000	£3,500-£5,000
Full Replacement - Rebuilt Engine with Forged Pistons	£6,500-£9,000	£3,800-£5,500
Replacement - Used Engine	£4,000-£5,500	£2,800-£4,000

Our recommendation

There is no minor repair for a cracked piston - the engine must come apart. On a W213 E 300 worth £10,000+, a specialist-supplied rebuilt engine with forged pistons is the only sensible long-term solution. The M274's piston cracking is a design weakness that used engines do not address - only a rebuilt unit with upgraded pistons eliminates the repeat failure risk. If you're considering a used E 300 purchase, factor a £3,800-£5,500 engine replacement into your budget - many owners have been caught out by this failure.

-> Compare rebuilt M274 Mercedes E Class 300 petrol engine prices

M256 Timing Chain Rattle

Affected: Mercedes E Class 450 (M256.930, 2018-present)
Typical failure mileage: 40,000 - 75,000 miles (reported as early as 20,000 miles)

Root cause

The M256's timing chain tensioners and guides can wear prematurely. M256 engines show timing component wear after 120,000 km. Cold-start rattling - described as "marbles in a can" - is the classic early warning sign. If ignored, failed guides can cause the chain to jump, skip a tooth and potentially snap, leading to catastrophic engine failure. The M256's timing chain is located at the rear of the engine, making replacement an engine-out job - significantly increasing labour costs.

Repair options

Repair tier	Dealer price	Specialist price
Preventative - Timing Chain Tensioner & Inspection	£1,000-£1,500	£600-£1,000
Major - Full Timing Chain Replacement	£3,500-£5,000	£2,200-£3,500
Full Replacement - Rebuilt Engine	£8,000-£12,000	£5,500-£8,500

Our recommendation

The cold-start rattle is your early warning - don't ignore it. A specialist timing chain replacement at £2,200-£3,500 is significantly cheaper than the £5,500+ engine replacement if the chain jumps. Given the £20,000+ value of most W213 E 450 examples, preventative chain work at 40,000-70,000 miles is a wise investment. The M256's rear-mounted timing chain makes this a complex job - ensure your specialist has M256 experience before committing.

-> Get M256 Mercedes E Class 450 timing chain quotes

M256 Oil Consumption & 48-Volt System Issues

Affected: Mercedes E Class 450 (M256.930, 2018-present)
Typical failure mileage: Variable - oil consumption reported at various mileages; 48-volt ground cable issues can occur at any time

Root cause

Like many turbocharged engines, the M256 has been reported to consume more oil than expected between service intervals. This may be caused by worn valve cover gaskets, oil cooler leaks, or degraded piston rings. The 48-volt mild-hybrid system adds significant complexity - the 48-volt ground cable connection in the engine compartment may not be tightened properly and can overheat. The integrated starter-generator (ISG) and electric auxiliary compressor (BorgWarner eBooster) are also potential failure points.

Repair options

Repair tier	Dealer price	Specialist price
Minor - Oil Top-Up & Monitoring	£0-£50	£0-£50
Intermediate - 48-Volt Ground Cable Replacement	£400-£800	£250-£500
Major - Oil Leak Repair (Valve Cover/Oil Cooler)	£800-£1,500	£500-£900
Full Replacement - Rebuilt Engine	£8,000-£12,000	£5,500-£8,500

Our recommendation

Oil consumption is a fact of life on turbocharged engines - regular oil level checks (every second fuel fill-up) are essential for the M256. If oil consumption exceeds 1 litre per 1,000 miles, have the valve cover and oil cooler inspected for leaks. The 48-volt system requires specialist diagnostic equipment - if you experience electrical issues or the EQ Boost system malfunctions, have it inspected promptly. The £250-£500 ground cable replacement is far cheaper than the £5,500+ engine replacement that a 48-volt system failure could indirectly cause.

-> Get M256 Mercedes E Class 450 oil consumption and 48-volt system quotes

M274 Timing Chain & Thermostat Failure

Affected: Mercedes E Class 300 (M274.920, 2016-2021)
Typical failure mileage: 60,000 - 100,000 miles

Root cause

The M274's timing chain and tensioner wear over time, particularly when oil change intervals are extended beyond 10,000 miles. The thermostat is a common failure point - its location under the engine makes replacement labour-intensive (approximately 3 hours). A failed thermostat prevents the engine from reaching operating temperature, increasing fuel consumption and emissions.

Repair options

Repair tier	Dealer price	Specialist price
Minor - Thermostat Replacement	£400-£700	£250-£450
Major - Full Timing Chain Replacement	£1,800-£2,800	£1,000-£1,800
Full Replacement - Rebuilt Engine	£6,500-£9,000	£3,800-£5,500

Our recommendation

The thermostat is a known weak point - if you notice the temperature gauge taking longer than usual to reach normal operating temperature, or if fuel consumption has increased, have it inspected. The cold-start rattle from the timing chain is your early warning - don't ignore it. A specialist timing chain replacement at £1,000-£1,800 is significantly cheaper than the £3,800+ engine replacement if the chain jumps. However, the piston cracking issue remains the primary concern on the M274 - timing chain issues are secondary.

-> Get M274 Mercedes E Class 300 timing chain and thermostat quotes

Don't Let Engine Failure Write Off Your Mercedes E Class 300 or 450 Modern Petrol

Whether your E Class 300 is suffering from piston failure or timing chain rattle, or your E 450 is experiencing cold-start timing chain noise or oil consumption issues, EnginesMarket makes it simple to compare prices from trusted UK Mercedes specialists. Every rebuilt engine in our network includes upgraded components designed to address the original failure point - plus a minimum 12-month unlimited mileage warranty and nationwide delivery. Compare prices, choose a specialist, and get back on the road without the main dealer premium.

Compare Mercedes E Class 300 / 450 Modern Petrol Engine Replacement Prices Now ->

FAQ

Mercedes E Class 300 / 450 Modern Petrol Engine ReplacementFrequently Asked Questions

Everything Mercedes Benz E Class 300 / 450 Modern Petrol owners usually ask before choosing a rebuilt, reconditioned or used replacement engine.

Short summary: Supply-only rebuilt M256 engines range from £5,500 to £8,500 depending on condition. With specialist fitting, budget £6,000-£9,300 total.

M274.920 (E 300, 245 hp, 2016-2021): rebuilt £3,800-£5,500
M256.930 (E 450, 367 hp with EQ Boost, 2018-present): rebuilt £5,500-£8,500
Labour adds £500-£1,000 depending on specialist location - the M256's rear-mounted timing chain makes it a more complex job

-> Compare Mercedes E Class 450 engine replacement costs by entering your reg now

Short summary: There are often no warning signs - the M274's piston cracking from LSPI is sudden and catastrophic. Some owners report a knocking noise or loss of power immediately before failure.

Loss of power or engine misfire
Knocking noise from the engine
Check engine light with misfire codes
There is no preventative fix - rebuilt engines with forged pistons are the only permanent solution

-> Get M274 Mercedes E Class 300 piston replacement quotes

Short summary: Yes, if the car is otherwise sound. W213 E 300 examples command £10,000-£22,000 used, while E 450 examples command £20,000-£40,000, making replacement viable【INDUSTRY ESTIMATE】.

A quality rebuilt M274 costs £3,800-£5,500 supply only
A quality rebuilt M256 costs £5,500-£8,500 supply only
The M256 is Mercedes' most advanced straight-six petrol engine
A replacement engine with warranty costs less than the depreciation on a newer car

-> Compare rebuilt Mercedes E Class 450 engine prices for your mileage and budget

Short summary: The M256's timing chain tensioners and guides can wear prematurely, causing cold-start rattling - described as "marbles in a can". M256 engines can show timing component wear after 120,000 km.

Timing chain rattle typically occurs between 40,000-75,000 miles
Cold-start rattling that disappears after a few seconds is the early warning
The timing chain is located at the rear of the engine - replacement is an engine-out job
Full timing chain replacement at a specialist costs £2,200-£3,500

-> Get quotes for M256 timing chain replacement before it's too late

Short summary: The M274 is a 2.0-litre turbocharged four-cylinder (E 300, 245 hp) with known piston cracking issues. The M256 is a 3.0-litre turbocharged straight-six (E 450, 367 hp) with EQ Boost mild-hybrid technology - more powerful, smoother, and generally more reliable.

M274: 2.0L four-cylinder, 245 hp, 370 Nm - prone to piston cracking, timing chain stretch, and thermostat failure
M256: 3.0L straight-six, 367 hp + 22 hp EQ Boost, 500 Nm - features 48-volt mild-hybrid system, electric auxiliary compressor, and integrated starter-generator
The M256 replaced the M276 V6 and is Mercedes' first petrol straight-six since the M104
The M256 is generally more reliable but more expensive to repair due to complexity

-> Find the correct Mercedes E Class petrol engine for your exact chassis and engine code

Short summary: With proper maintenance and 8,000-10,000 mile oil changes, M256 engines regularly reach 150,000-200,000+ miles. The M256 is a modern, efficient design with a robust bottom end.

M256 straight-six is a modular design sharing architecture with four-cylinder and V8 engines
Timing chain inspection/replacement at 40k-75k miles is recommended if rattle occurs
Regular oil changes (8,000 miles) are critical for timing chain life
The M256 is generally considered more reliable than the M274

-> Compare Mercedes E Class 450 engine replacement quotes - be ready when the time comes

Why Choose Us

Compare Mercedes E Class 300 / 450 Modern Petrol Engine Prices Today

Comparing quotes for your Mercedes E Class 300 or 450 modern petrol engine replacement is free, no-obligation, and specific to your exact engine code and model year. Enter your registration above to get tailored prices from vetted UK specialists - whether you need a used M274.920, a reconditioned M256.930 with forged pistons, or a fully rebuilt unit with warranty and fitting. Don't pay main dealer premiums - compare, choose, and get back on the road with confidence.

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Compare quotes from trusted UK Mercedes Benz E Class 300 / 450 Modern Petrol engine specialists with warranty-backed rebuilt, reconditioned and used options nationwide.

Mercedes Benz E Class 300 / 450 Modern Petrol Engine Replacement Compare Prices & Get Quotes

Get your free Mercedes Benz e-class 300 / 450 Modern Petrol engine quotes

3 Simple Steps to Finding the Right Replacement Engine

Mercedes Benz E Class 300 / 450 Modern Petrol Engine History & Specs at a Glance

Mercedes Benz E Class 300 / 450 Modern Petrol Engine Codes Specifications & Replacement Cost

M274.920 — 2.0L Turbo Petrol (2016-2021)

Mercedes E Class 300 / 450 Modern Petrol Engine Problems Repair Cost vs Replacement

M274 Piston Cracking

M256 Timing Chain Rattle

M256 Oil Consumption & 48-Volt System Issues

M274 Timing Chain & Thermostat Failure

Don't Let Engine Failure Write Off Your Mercedes E Class 300 or 450 Modern Petrol

Mercedes E Class 300 / 450 Modern Petrol Engine ReplacementFrequently Asked Questions

Compare Mercedes E Class 300 / 450 Modern Petrol Engine Prices Today