Mercedes Benz GLS Class 350d/400d Engine ReplacementCompare Prices & Get Quotes

Short summary: A rebuilt OM642 engine for the GLS 350d costs £3,800-£5,500 supply-only; a rebuilt OM656 engine for the GLS 400d costs £5,500-£7,200 supply-only. Fitting adds £1,200-£2,500 depending on complexity - both V6 and straight-six work requires specialist knowledge.

• GLS 350d (OM642.826): rebuilt unit £3,800-£5,500; used engine from £1,800
• GLS 400d (OM656.929): rebuilt unit £5,500-£7,200; used engine from £2,500
• OM642 oil cooler seal replacement (labour only): £900-£1,400 at specialist
• OM656 AdBlue heater pump replacement: £400-£750 at specialist

Short summary: A burnt-oil smell after highway driving or oil pooling in the V of the engine is the classic warning sign. The oil seals themselves are a low-cost item; the labour to replace them is the significant expense. If ignored, coolant contamination leads to bearing washout and terminal engine seizure.

• Burnt-oil smell from the engine bay after highway driving
• Oil pooling in the valley between V6 cylinder banks
• Oil dripping onto the exhaust system
• If caught early, Viton seal replacement costs £900-£1,400 at specialist

Short summary: The OM656 straight-six is a modern, powerful diesel with excellent performance - 330hp and 700Nm torque. However, it has known AdBlue/SCR system issues and EGR cooler problems that can trigger warning lights and start limitations. With recalls addressed and proper maintenance, these engines are proving durable.

• AdBlue heater pump failure can trigger countdown warnings
• EGR system can suffer from carbon build-up
• Turbo actuator hose failure has been reported
• Well-maintained OM656 engines exceed 150,000 miles

Short summary: Properly maintained OM642 V6 diesels routinely reach 150,000-200,000+ miles before major work. The OM656 straight-six is too new for definitive long-term data, but with AdBlue issues addressed, similar longevity is expected.

• OM642 (350d): 150,000-200,000+ miles with regular servicing
• OM656 (400d): too early for definitive data - AdBlue and EGR issues from 40k-70k miles
• Service interval is 10,000 miles or 12 months - use Mercedes-spec low-SAPS oil (MB 229.52)
• Late oil changes accelerate oil cooler seal failure on OM642 and AdBlue issues on OM656

Short summary: Yes, if the GLS is otherwise in good condition with no rust or major electrical or transmission faults. A rebuilt OM642 costs £3,800-£5,500 - far less than replacing a £15,000-£30,000 vehicle. The GLS 400d's higher value (£35,000-£60,000) makes replacement even more financially justifiable.

• GLS 350d values: £15,000-£30,000 depending on year, mileage and condition
• GLS 400d values: £35,000-£60,000 - premium SUV residual values remain strong
• Rebuilt engine with upgraded components fixes original weak points
• Supply & fit typically £5,000-£9,700 depending on engine code
• New engine includes 12-month unlimited mileage warranty

Short summary: Mercedes-Benz specifies low-SAPS oil meeting MB 229.51 or 229.52 - typically 5W-30. The OM642 V6 requires approximately 8.5 litres; the OM656 straight-six requires approximately 7.5 litres.

• OM642 (350d): MB 229.51/229.52 5W-30 low-SAPS - protects DPF and emissions systems
• OM656 (400d): MB 229.52 5W-30 low-SAPS - 7.5L capacity
• Never use non-approved oil - can cause excessive soot buildup
• Change every 10,000 miles or 12 months - stretched intervals cause oil cooler seal degradation and turbo wear