Mercedes-Benz C-Class 300d Engine Replacement Compare Prices & Get Quotes

A replacement OM654 engine for a C300d typically costs between £1,200 and £5,500 depending on condition. Used units start from £1,200-£2,800, reconditioned from £2,800-£4,800, and fully rebuilt from £3,000-£5,500. Labour for supply & fit adds £500-£1,000.

• Used OM654.920 (W205 C300d): £1,200-£2,500
• Reconditioned OM654.920: £2,800-£4,500
• Rebuilt OM654.820 (W206 C300d): £3,200-£5,500

The C300d uses the OM654 engine, which has a timing chain, not a belt. The chain is generally robust, but individual bolts or chain links of the camshaft timing chain might wear in case of long-term operation under specific driving conditions, potentially leading to a tear. A metallic rattling noise on cold start is the classic warning sign.

• OM654: timing chain - durable but can wear at higher mileages
• Regular oil changes are critical for chain longevity
• Rattling on cold start should be inspected immediately

Common signs of engine problems in the C300d include: a "No Start in XXX miles" countdown warning (AdBlue system failure), reduced power or limp mode (EGR cooler or turbo issues), a rattling noise on cold start (timing chain wear), and coolant leaks or warning lights (coolant pump/vacuum circuit recall issue on 2017-2021 models). If you experience any of these, have the car inspected immediately.

• Countdown warning - AdBlue system failure
• Loss of power - EGR or turbo issues
• Rattling on cold start - timing chain wear

It depends on the car's condition and mileage. A W205 C300d is typically worth £10,000-£22,000 - a rebuilt OM654 engine (£3,000-£5,200) is usually well within the car's value and can be a worthwhile investment if the car is in good condition. A W206 C300d is worth £25,000-£45,000 - a rebuilt OM654.820 engine (£3,200-£5,500) is easily justified. For lower-value examples, an AdBlue or EGR repair is often more economical than a full replacement.

• W205 (2018-2021): rebuilt engine viable for good condition cars
• W206 (2021-present): rebuilt engine usually justifies cost
• AdBlue/EGR repairs: often more economical than full replacement

Both engines are 2.0-litre four-cylinder diesels from the OM654 family, but with different power outputs and applications. The OM654.920 is used in the W205 C300d (2018-2021), producing 241 hp and 500 Nm of torque. The OM654.820 is used in the W206 C300d (2021-present), producing 261 hp and 550 Nm of torque. The OM654.820 also features an integrated starter-generator (ISG) mild hybrid system.

• OM654.920: 241 hp, 500 Nm, W205 (2018-2021)
• OM654.820: 261 hp, 550 Nm, W206 (2021-present), with ISG mild hybrid

The AdBlue system on the C300d can fail due to crystallisation in the dosing injector, a failed heater element in the AdBlue tank, or degraded NOx sensors. The ECU responds with a "No Start in XXX miles" countdown when AdBlue dosing is compromised. Common fault codes include P202E84 (AdBlue metering valve malfunction) and P20F409 (AdBlue consumption too low). Mercedes issued a recall for 2017-2021 models with OM654 engines due to a potential coolant leak between the coolant pump and the vacuum circuit.

• AdBlue heater failure - common on 2018-2020 models
• NOx sensor degradation - sensors have a limited service life
• Countdown warning - do not ignore; seek specialist diagnosis