Mercedes-Benz C-Class 250 CDI Engine Replacement Compare Prices & Get Quotes

A replacement OM651 engine for a C250 CDI typically costs between £800 and £5,200 depending on condition. Used units start from £800-£1,900, reconditioned from £2,500-£4,400, and fully rebuilt from £2,800-£5,200. A replacement OM651.912 engine costs on average £3,850 in good condition, with reconditioned units costing up to £4,409. Labour for supply & fit adds £500-£1,000.

• Used OM651.911: £800-£1,800
• Reconditioned OM651.912: £2,600-£4,400
• Rebuilt OM651.911: £2,800-£5,000

The C250 CDI uses the OM651 engine, which has a single timing chain at the rear of the engine. Unlike the front-mounted duplex chains on earlier OM646 engines, the OM651's rear-mounted chain is prone to stretching. A metallic rattling noise on cold start is the classic warning sign. Some owners have reported chain failure at 90,000 miles, with failure typically occurring between 80,000-120,000 miles.

• OM651: rear-mounted single timing chain - prone to stretch at 80k-120k miles
• Rattling on cold start is the warning sign
• Regular oil changes are critical for chain longevity

On OM651-equipped C250 CDI models, the most common symptom is a rattling or clattering noise from the rear of the engine on cold start. Other signs include loss of power, rough idle, engine misfires, and the engine management light illuminating. If you hear any unusual sounds, have the timing system inspected immediately - ignoring the rattle can lead to catastrophic engine failure.

• Cold-start rattle from the rear of the engine
• Loss of power and rough running
• Engine management light activation

It depends on the car's condition and mileage. A W204 C250 CDI is typically worth £4,000-£10,000 - a rebuilt OM651 engine (£2,800-£5,200) can be a worthwhile investment if the car is in good condition. The C250 CDI's strong performance and desirable specification often justify engine replacement. For lower-value examples or those with multiple issues, a specialist repair (timing chain, injector seals) may be more economical than a full replacement.

• W204 (2008-2014): rebuilt engine with warranty is viable for good condition cars
• Vehicle worth over £5,000: replacement usually justifies the cost
• Preventative timing chain replacement: often more economical than full replacement

Both the C250 CDI and C220 CDI use the OM651 2.1-litre diesel engine, but with significant differences in specification. The C250 CDI produces 204 hp and 500 Nm of torque, compared to the C220 CDI's 170 hp and 400 Nm. The C250 CDI achieves this through a two-stage turbocharging system with a larger main turbo and higher-flow injectors, combined with a smaller turbo for quick low-end response. The result is a 0-62 mph time of 7.0 seconds for the C250 CDI versus 8.4 seconds for the C220 CDI.

• C250 CDI: 204 hp, 500 Nm, two-stage turbo, 0-62 in 7.0s
• C220 CDI: 170 hp, 400 Nm, single-stage turbo, 0-62 in 8.4s
• Same 2.1L OM651 architecture, different turbo and injector hardware

Power loss in the C250 CDI is most commonly caused by turbocharger issues, particularly sticking variable vanes on the two-stage turbo system. Other causes include EGR valve clogging, injector seal failure ("Black Death"), and timing chain stretch causing cam timing drift. The two-stage turbo system adds complexity - if the small turbo fails to spool or the large turbo loses boost, power drops significantly. A diagnostic check with Mercedes STAR or compatible equipment is essential to identify the exact cause.

• Turbocharger vanes - sticking from carbon buildup
• EGR valve - clogging from carbon deposits
• Injector seals - "Black Death" causing compression loss
• Timing chain stretch - power loss + rattling