Mercedes-Benz C-Class 270 CDI / 300 CDI Engine Replacement Compare Prices & Get Quotes

A replacement engine for a C270 CDI or C300 CDI typically costs between £600 and £5,000 depending on the engine code and condition. Used OM612 units start from £600-£1,400, reconditioned from £1,800-£3,000, and fully rebuilt OM642 engines from £2,800-£5,000. Labour for supply & fit adds £500-£1,000.

• Used OM612.962 (W203 C270 CDI): £600-£1,400
• Rebuilt OM612.962: £2,200-£3,800
• Rebuilt OM642.832 (W204 C300 CDI): £2,800-£5,000

"Black Death" refers to injector seal failure that affects OM612 engines. The copper washer seal between the injector and cylinder head degrades, allowing combustion gases to escape. This creates hard, black carbon deposits around the injector. Symptoms include a ticking or chuffing noise, a strong diesel smell in the cabin, hissing sounds from the engine, and visible black tar-like residue. If left untreated, the injector can seize in the cylinder head, requiring expensive extraction and head repairs.

• Affects OM612 engines in W203 C270 CDI
• Early repair (£180-£300 per injector) prevents injector seizure
• Ignoring it can lead to £1,400+ head repair costs

Both the OM612 (C270 CDI) and OM642 (C300 CDI) use timing chains, not belts. The OM612 features a front-mounted duplex roller chain, which is generally robust with a service life of 200,000-250,000 kilometres. The OM642 features a duplex roller chain per cylinder bank. Neither has a scheduled replacement interval, but tensioner wear can occur at higher mileages.

• OM612: front-mounted duplex timing chain - durable, 200k+ km life
• OM642: duplex roller chain per cylinder bank - robust
• Rattling on cold start may indicate tensioner wear

It depends on the generation and condition. A W203 C270 CDI is typically worth £1,500-£4,000 - a full engine replacement often exceeds the car's value, making a used engine or targeted repair (injector seals, fuel pump) more economical. A W204 C300 CDI is worth £5,000-£12,000 - a rebuilt OM642 engine (£2,800-£5,000) can be a worthwhile investment if the car is in good condition. Always compare the cost of repair against the car's market value.

• W203 (2000-2005): used engine or targeted repair
• W204 (2011-2014): rebuilt engine with warranty is viable for good condition cars
• Vehicle worth over £4,000: replacement usually justifies the cost

The C270 CDI uses the OM612 2.7-litre five-cylinder diesel (170 hp, 400 Nm), fitted to the W203 generation from 2000-2005. The C300 CDI uses the OM642 3.0-litre V6 diesel (231 hp, 540 Nm), fitted to the W204 generation from 2011-2014. The OM642 offers significantly more power and refinement but has a well-documented oil cooler seal leak. The OM612 is a simpler design with fewer complex emissions systems.

• OM612 (C270 CDI): 2.7L, 5-cyl, 170 hp, 400 Nm, W203 (2000-2005)
• OM642 (C300 CDI): 3.0L, V6, 231 hp, 540 Nm, W204 (2011-2014)
• OM642 has oil cooler seal leak weakness; OM612 has injector seal issues

The C300 CDI's OM642 V6 engine is known for oil cooler seal failure, which causes oil to leak from the Vee of the engine. Symptoms include a "Check Oil Level" message, decreasing oil level measurements, and oil stains or puddles underneath the vehicle. The leak is very difficult to inspect from the top of the engine, and most owners discover it when oil starts dripping from the back of the engine. Mercedes Service Bulletin LI18.30-P-055434 addresses this issue.

• Oil cooler seal failure - common on OM642 at 70k-120k miles
• "Check Oil Level" message - first warning sign
• Repair at specialist: £800-£1,200