Mercedes Benz S Class 300/320 CDI Engine Replacement Compare Prices & Get Quotes

Short summary: A rebuilt OM642 engine for the S 320 CDI costs £2,200-£3,500 supply-only; a rebuilt OM651 engine for the S 300 CDI costs £2,000-£3,000 supply-only. Fitting adds £1,200-£2,500 depending on complexity.

• S 320 CDI (OM642.930/931/932): rebuilt unit £2,200-£3,500; used engine from £1,200
• S 300 CDI (OM651): rebuilt unit £2,000-£3,000; used engine from £1,000
• OM642 timing chain replacement (labour only): £1,800-£2,800 at specialist
• OM642 oil cooler seal replacement: £950-£1,400 at specialist

Short summary: A rattling noise on cold start or intermittent starting problems are the classic warning signs on the OM642 engine. One owner reported a timing chain failure at only 56,000 miles.

• Cold start rattle that disappears after oil pressure builds - earliest warning
• Intermittent starting - engine cranks but fails to start; timing chain stretch causes cam and crank sensors to misalign
• Check engine light with timing correlation codes
• If caught early, chain replacement costs £1,800-£2,800 at specialist

Short summary: The OM642 V6 is fundamentally robust, but S 320 CDI owners should be aware of timing chain stretch and oil cooler seal degradation. With these addressed, the engine is capable of 150,000+ miles.

• OM642 V6 is fundamentally robust with proven durability
• Timing chain stretch is the most critical failure point - can occur as early as 56,000 miles
• Oil cooler seal degradation affects many units from 80,000 miles
• Well-maintained OM642 engines exceed 150,000 miles

Short summary: Properly maintained OM642 engines routinely reach 150,000-200,000 miles before major work is needed. The OM651 is also durable but requires attention to injector seals.

• OM642 (S 320 CDI): 150,000-200,000+ miles with regular servicing
• OM651 (S 300 CDI): 150,000+ miles with regular servicing
• Timing chain inspection recommended from 80,000 miles on OM642
• Service interval is 10,000 miles or 12 months - use Mercedes-spec low-SAPS oil (MB 229.51)

Short summary: Yes, if the S Class is otherwise in good condition with no rust or major transmission faults. A rebuilt OM642 costs £2,200-£3,500 - comparable to the value of a £4,000-£12,000 vehicle, making it a justifiable investment for well-maintained examples.

• S 320 CDI values: £4,000-£12,000 depending on year, mileage and condition
• S 300 CDI values: £3,000-£8,000
• Rebuilt engine with upgraded components fixes original weak points
• Supply & fit typically £3,400-£6,000 depending on engine code
• New engine includes 12-month unlimited mileage warranty

Short summary: Mercedes-Benz specifies low-SAPS oil meeting MB 229.51 - typically 5W-30. The OM642 V6 requires approximately 8.5 litres with filter; the OM651 requires approximately 6.5 litres.

• OM642 (S 320 CDI): MB 229.51 5W-30 low-SAPS
• OM651 (S 300 CDI): MB 229.51 5W-30 low-SAPS - 6.5L capacity
• Never use non-approved oil - can cause timing chain and injector issues
• Change every 10,000 miles or 12 months - stretched intervals cause timing chain wear