Mercedes Benz S Class Engine ReplacementCompare Prices & Save

Key points

• • OM642 and OM656 diesel engines: £1,800-£4,300 rebuilt supply-only
• • M276 and M278 petrol V6/V8 units: £2,300-£5,500 typical range
• • AMG M177 and M279 performance engines: £4,800-£11,500 specialist rebuild
• • Supply & fit labour adds £1,200-£2,500 depending on garage location
• • All EngineMarket quotes include minimum 12-month unlimited mileage warranty

Key points

• • Failure typically occurs between 60,000-90,000 miles on S350d and S400d models
• • Coolant mixing with exhaust gases triggers warning lights and reduced power
• • Reinforced brazing upgrade part A6560940001 addresses the design weakness
• • Specialist rebuilds include upgraded EGR components to prevent recurrence

Key points

• • Factory composite guide rails degrade under high thermal cycling loads
• • Updated guide kit part A2780500112 provides improved long-term durability
• • Chain stretch can cause timing misalignment and valve damage if unchecked
• • Rebuilt M278 units include hardened guides and precision balancing

Key points

• • Oil cooler seal leaks typically appear between 80,000-110,000 miles
• • Multi-layer steel gasket upgrades resolve seepage without full engine removal
• • Injector coking causes hard starting; ultrasonic cleaning or replacement restores performance
• • Well-maintained OM642 units routinely exceed 150,000 miles in S350 CDI applications

Key points

• • Used engines: £1,800-£3,000 but variable condition and limited warranty coverage
• • Reconditioned units: £2,400-£4,500 with worn parts replaced to OEM-spec tolerances
• • Bench testing and dyno certification validate performance before dispatch
• • Reconditioned engines address known failure points proactively during rebuild

Key points

• • OM656 features aluminium block, stepped-bore tech and improved thermal management
• • M256 mild-hybrid system reduces mechanical load via EQ Boost assistance
• • Avoid early M276 units (pre-2015) without updated timing chain tensioners
• • Regular oil changes with MB-approved spec 229.51/229.52 extend all engine lifespans

Key points

• • Cold-start rattle lasting over 30 seconds suggests timing component wear
• • Milky oil or coolant loss indicates head gasket or cooler seal failure
• • Check-engine lights with P0087/P0088 codes signal high-pressure fuel pump issues
• • Professional compression and leak-down testing confirms internal damage severity

Key points

• • 48V Belt-Driven Starter Generator requires specialist diagnostic tools for integration
• • EQ Boost software mapping must match engine serial number and vehicle VIN
• • High-voltage safety protocols mandate certified technician handling during removal
• • EngineMarket suppliers coordinate HV system checks as part of rebuilt unit supply

Key points

• • OM642 fits W221 only; OM656 is W222/W223 specific with different ancillary layouts
• • M278 and M176 share displacement but differ in turbo placement and ECU mapping
• • 4MATIC AWD models require flash file verification (A6569000004/A2789000002) for calibration
• • Enter your registration to confirm exact engine code and generation compatibility instantly

Key points

• • Independent specialist rebuilds are recognised by UK insurers when documented properly
• • OEM-spec warranty terms match main dealer coverage for peace of mind
• • Retain all invoices and dyno certificates for future resale or claim validation
• • Notify your insurer of the replacement; most premium policies accommodate specialist repairs