Mercedes Benz S Class 350/450 Petrol Engine Replacement Compare Prices & Get Quotes

Short summary: A rebuilt M276 engine for the S 350 costs £3,200-£4,500 supply-only; a rebuilt M256 engine for the S 450 costs £4,200-£5,400 supply-only. Fitting adds £1,200-£2,500 depending on complexity - both engines require specialist knowledge.

• S 350 (M276.950): rebuilt unit £3,200-£4,500; used engine from £1,500
• S 450 (M256.930): rebuilt unit £4,200-£5,400; used engine from £2,200
• M276 timing chain tensioner replacement: £700-£1,200 at specialist
• M256 wiring harness replacement: £800-£1,400 at specialist

Short summary: A rattling noise on cold start lasting a few seconds is the classic warning sign on the M276 V6 engine. The hydraulic secondary chain tensioners can lose oil pressure, allowing chain slack.

• Cold start rattle that disappears after oil pressure builds - earliest warning
• Check engine light with timing correlation codes
• Mercedes TSB LI05.10-P-056435 covers updated tensioners and check valves
• If caught early, tensioner replacement costs £700-£1,200 at specialist

Short summary: The M256 inline-six is a modern, sophisticated engine, but it has known wiring harness degradation issues and 48V system vulnerabilities. With these addressed, the engine is proving durable.

• Wiring harness degradation near turbocharger is the most common electrical issue
• 48V battery and ISG failures can cause warning lights and loss of EQ Boost
• Oil consumption between services has been reported
• Well-maintained M256 engines exceed 100,000 miles

Short summary: Properly maintained M276 V6 engines routinely reach 150,000-200,000 miles before major work. The M256 is too new for definitive long-term data, but with proactive maintenance, 100,000+ miles is achievable.

• M276 (S 350): 150,000-200,000 miles with regular servicing
• M256 (S 450): too early for definitive data - wiring and 48V issues from 30k-60k miles
• Service interval is 10,000 miles or 12 months - use Mercedes-spec MB 229.5 oil
• Late oil changes accelerate timing chain wear on M276 and wiring degradation on M256

Short summary: Yes, if the S-Class is otherwise in good condition with no rust or major electrical faults. A rebuilt M276 costs £3,200-£4,500 - far less than replacing an £8,000-£18,000 vehicle. The S 450's higher value (£35,000-£60,000) makes replacement even more financially justifiable.

• S 350 values: £8,000-£18,000 depending on year, mileage and condition
• S 450 values: £35,000-£60,000 - flagship residual values remain strong
• Rebuilt engine with upgraded components fixes original weak points
• Supply & fit typically £4,400-£7,900 depending on engine code
• New engine includes 12-month unlimited mileage warranty

Short summary: Mercedes-Benz specifies MB 229.5 high-performance oil - typically 5W-30 or 5W-40 fully synthetic. The M276 V6 requires approximately 7.5 litres; the M256 inline-six requires approximately 8.0 litres.

• M276 (S 350): MB 229.5 5W-30 or 5W-40 - 7.5L capacity
• M256 (S 450): MB 229.5 5W-30 or 5W-40 - 8.0L capacity
• Never use non-approved oil - can cause timing chain and hydraulic lifter issues
• Change every 10,000 miles or 12 months - stretched intervals cause timing chain wear