Mercedes-Benz C-Class 320 CDI / 350 CDI Engine Replacement Compare Prices & Get Quotes

A replacement OM642 engine for a C320 CDI or C350 CDI typically costs between £600 and £5,200 depending on condition. Used units start from £600-£2,200, reconditioned from £1,800-£4,400, and fully rebuilt from £2,200-£5,200. Labour for supply & fit adds £500-£1,000.

• Used OM642.910 (W203 C320 CDI): £600-£1,400
• Rebuilt OM642.960 (W204 C320/CDI/C350 CDI): £2,500-£4,500
• Rebuilt OM642.834 (W204 C350 CDI BlueEFFICIENCY): £2,800-£5,000

The most common problem is oil cooler seal failure, typically occurring at 70,000-120,000 miles. The seals degrade over time, causing oil to leak from the Vee of the engine. Symptoms include a "Check Oil Level" message, decreasing oil levels, and oil stains or puddles underneath the vehicle. Mercedes Service Bulletin LI18.30-P-055434 addresses this issue. Repair costs at a specialist are approximately £800-£1,200.

• Oil cooler seal failure - most common OM642 issue
• "Check Oil Level" message - first warning sign
• Repair at specialist: £800-£1,200

Both the C320 CDI and C350 CDI use the OM642 V6 diesel engine, which has a timing chain, not a belt. The OM642 features a duplex roller chain per cylinder bank. Neither has a scheduled replacement interval, but tensioner wear can occur at higher mileages. A rattling noise on cold start may indicate timing chain tensioner wear.

• OM642: duplex roller timing chain - robust
• No scheduled replacement interval
• Rattling on cold start may indicate tensioner wear

It depends on the generation and condition. A W203 C320 CDI is typically worth £2,000-£5,000 - a full engine replacement often exceeds the car's value, making a used engine or targeted repair (oil cooler seals, swirl flap motor) more economical. A W204 C350 CDI is worth £4,000-£10,000 - a rebuilt OM642 engine (£2,800-£5,200) 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 (2004-2007): used engine or targeted repair
• W204 (2007-2014): rebuilt engine with warranty is viable for good condition cars
• Vehicle worth over £4,000: replacement usually justifies the cost

Both use the OM642 3.0-litre V6 diesel architecture, but with different power outputs. The C320 CDI (W203, 2004-2007) produces 221 hp (165 kW) and 510 Nm torque. The C320 CDI (W204, 2007-2011) produces 224 hp (165 kW). The C350 CDI BlueEFFICIENCY (2011-2014) produces 231 hp (170 kW) and 540 Nm torque. The later C350 CDI 4MATIC (OM642.832) produces 265 hp (195 kW) in some markets. The C350 CDI benefits from revised turbocharging and ECU calibration for improved performance.

• C320 CDI: 221-224 hp, 510 Nm, W203/W204 (2004-2011)
• C350 CDI: 231-265 hp, 540 Nm, W204 (2011-2014)
• Same 3.0L V6 architecture, different tuning

Power loss in the C320 CDI and C350 CDI is most commonly caused by turbocharger issues (sticking variable vanes), EGR valve clogging, or swirl flap motor failure. The swirl flap motor failure can trigger fault codes and reduce power, with repair costs at a specialist quoted at approximately £2,000-£3,000. A diagnostic check with Mercedes STAR or compatible equipment is essential to identify the exact cause.

• Turbocharger vanes - sticking from carbon buildup
• Swirl flap motor - failure causing reduced power
• EGR valve - clogging from carbon deposits