2018 Mercedes-Benz C 2.1L Diesel · HY18 DCX

The 2.1-litre diesel C-Class typically returns 50-60 mpg in real-world mixed driving, which is one of its strongest selling points. Road tax falls in a moderate band for a Euro 6 diesel of this age — expect around £20-£165 annually depending on the exact VariantApproval rate listed on the V5C. Insurance for the C-Class usually sits in groups 20-32, so a typical 40-year-old buyer might pay £450-£650 per year fully comprehensive.

Servicing at a Mercedes main dealer is expensive (often £400-£700 per visit), but independent specialists familiar with Mercedes diesels typically charge £200-£350. Common maintenance items include brake discs and pads (£350-£500 for a full axle refurbishment at a specialist), diesel particulate filter cleaning or replacement (a major cost item if needed, £800-£1,500), and AdBlue system maintenance. The 2.1-litre engine's cambelt, if not chain-driven on your variant, should be replaced every 5 years or 75,000 miles.

Estimated annual running cost is approximately £1,400-£1,800 covering fuel, tax, insurance, and a modest maintenance allowance. This is competitive for the executive saloon class, particularly given the strong fuel economy figures.

Start with the engine management system. The 2024 MIL failure is the most significant item in the MOT history, so plug in an OBD-II scanner or pay for a diagnostic check to confirm no active or stored codes related to DPF, EGR, AdBlue, or turbo boost pressure. These are the most common fault areas on the OM651 2.1-litre diesel. Cold-start the vehicle and watch for excessive smoke from the exhaust — blue or heavy grey smoke indicates oil or turbo issues.

Inspect the underside and engine bay for signs of oil leaks, particularly around the front crankshaft seal and turbo oil return pipe, both known OM651 weak spots. Check the condition of the timing chain by listening for a rattle on cold start — a stretched chain on these engines can lead to expensive repairs if left unchecked. The diesel particulate filter should also be assessed; short journeys primarily can clog the DPF, so ask about the vehicle's typical usage pattern.

Finally, examine the bodywork for the white paint's condition (stone chips are common on the bonnet and front bumper), check all electrical features including the infotainment system and Command unit, and verify the operation of the AdBlue dosing system by checking the dashboard for low-AdBlue warnings. A test drive of at least 20 minutes including some dual-carriageway miles will help reveal any turbo, DPF, or transmission issues that a quick blast around the block would miss.