Mercedes Benz CLS 320/350 CDI Engine ReplacementCompare Prices & Get Quotes

A Mercedes CLS 320 CDI or CLS 350 CDI replacement engine typically costs between £2,200 for a used unit and £5,800 for a fully rebuilt OM642 engine. Specialist fitting adds £450-£900.

• Used OM642 engines: £2,200-£4,200 depending on mileage and condition
• Reconditioned units: £3,200-£5,200 supply only
• Rebuilt units: £3,800-£5,800 with 12-month warranty
• Specialist fitting adds £450-£900; dealer labour is significantly higher
• 12-month warranty included on all rebuilt units through EnginesMarket

The OM642 V6 diesel is fundamentally robust and capable of 200,000+ miles, but it has a well-documented Achilles heel: oil cooler seal failure that allows coolant to mix with oil. Catch it early and it's a great engine.

• Oil cooler seals fail at 70,000-120,000 miles - the £5 part that costs £650-£950 to replace
• Timing chain stretch can occur from 75,000 miles
• Swirl flap motor and turbo actuator failures are common on higher-mileage units
• Preventative seal replacement is strongly recommended

The OM642 V6 engine has rubber oil cooler seals at the centre of the Vee that degrade and leak. When they fail, they cause oil to mix with coolant - a £5 part that requires 9 hours of labour to replace.

• Oil cooler sits "in the bowels of hell deep down in the 'V' of the engine"
• Symptoms: oil traces in the inner-V, oil leaks at drain points
• Original orange seals replaced with updated purple seals
• Specialist seal replacement costs £650-£950
• If ignored, coolant contamination can destroy the engine

Well-maintained OM642 engines regularly exceed 200,000-300,000 miles. The OM642 is a robust engine that, with proper maintenance, can deliver exceptional longevity.

• OM642: 200k-300k+ miles with regular servicing
• Oil cooler seals need replacing once - typically at 70k-120k miles
• Regular oil changes every 10,000 miles are critical for longevity
• 2009-2010 chain redesigns led to accelerated wear on some units

Timing chain replacement on a CLS 320/350 CDI OM642 engine costs £1,400-£2,000 at a specialist or £2,000-£3,000 at a main dealer. This is preventative work. If the chain has already slipped, full engine replacement at £3,800-£5,200 is required.

• Specialist preventative chain replacement: £1,400-£2,000
• Dealer pricing for same work: £2,000-£3,000
• The OM642 uses a duplex roller chain drive
• Rattling noise on cold start is the early warning sign

On a CLS 320/350 CDI worth £4,700-£15,000, specialist engine replacement at £3,800-£5,200 is worthwhile if the body and interior are in excellent condition. However, if the car has rust, electrical issues, or poor bodywork, consider scrapping it.

• A clean, well-maintained CLS is worth saving
• Rebuilt OM642 with upgraded Viton seals and timing components costs £3,800-£5,800 supply only
• If the car has other major issues, replacement may not be cost-effective
• "A 15 yr old £3k car is not really the sort of car that a main dealer can look after in any sensible way"

Both use the same OM642 engine family. The CLS 320 CDI produces 224 hp (2005-2010), while the CLS 350 CDI produces 224-265 hp depending on generation. The later C218 CLS 350 CDI (2011-2017) uses a twin-turbo version producing 265 hp and 620 Nm.

• Same engine block, cylinder head and bottom end
• Power difference is turbocharger specification and engine mapping
• The C219 CLS 350 CDI (2009-2010) has the same 224 hp output as the 320 CDI
• The C218 CLS 350 CDI (2011-2017) is a significantly different 265 hp twin-turbo unit