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

A Mercedes CLS 350 d or CLS 400 d replacement engine typically costs between £3,200 for a used unit and £7,500 for a fully rebuilt OM656 engine. Specialist fitting adds £800-£1,500.

• Used OM656 engines: £3,200-£5,000 depending on mileage and condition
• Reconditioned units: £4,500-£6,500 supply only
• Rebuilt units: £5,500-£7,500 with 12-month warranty
• Specialist fitting adds £800-£1,500; dealer labour is significantly higher
• 12-month warranty included on all rebuilt units through EnginesMarket

The OM656 inline-six diesel is a sophisticated and refined engine, but it has known weak points. Camtronic variable valve timing failure is the most significant issue, with water pump failures and CP4 fuel system sensitivity also reported.

• Camtronic failure can occur from 40,000-80,000 miles
• Water pump failures have been reported, particularly after recalls
• Bosch CP4 fuel system is sensitive to poor-quality diesel
• Oil consumption and digital oil level issues are common complaints
• Regular servicing with high-quality parts and fuel is essential

The OM656 engine uses Camtronic variable valve timing, which controls camshaft profiles using electromagnets. In the event of a failure, the drive electromagnets, controlled camshaft and rocker arms require replacement.

• Symptoms: rough running, loss of power, engine warning lights
• Specialist Camtronic component replacement costs £1,000-£1,800
• If ignored, valvetrain damage can occur, requiring full engine replacement
• Catch it early - the repair is far cheaper than engine replacement

Yes, some OM656 engines have been reported to consume oil at higher than expected rates. The digital oil level readout can also be unreliable, with levels appearing to drop suddenly.

• Engine oil capacity is 8.5 litres
• Some owners have reported draining only 4 litres of oil
• Digital oil level sensor can fail
• A physical dipstick is no longer fitted - rely on the digital readout or manual checks

The OM656 engine has an estimated lifespan of approximately 250,000 km (155,000 miles). With proper maintenance, many units will exceed this, but Camtronic and fuel system failures can occur earlier.

• Estimated engine lifespan: ~250,000 km
• Camtronic failure can occur from 40,000-80,000 miles
• Regular oil and filter changes using Mercedes-approved 5W-30 oil are critical
• Using high-quality diesel fuel prevents CP4 pump and injector issues

On a CLS 350/400 d worth £25,000-£40,000, specialist engine replacement at £5,500-£7,500 is worthwhile if the body and interior are in excellent condition. With vehicle values in this bracket, replacement is almost always justifiable.

• A clean, well-maintained CLS is worth saving
• Rebuilt OM656 with upgraded components costs £5,500-£7,500 supply only
• Compare against £7,500-£10,000 main dealer new engine quotes
• If the car has other major issues, replacement may not be cost-effective

Both use the same OM656.929 engine family. The CLS 350 d produces 286 hp and 600 Nm, while the CLS 400 d produces 340 hp and 700 Nm.

• Same engine block, cylinder head and bottom end
• Power difference is turbocharger specification and engine mapping
• Reliability is similar between the two variants
• Both are 4MATIC all-wheel drive only