2012 MERCEDES-BENZ C250 W204

Typical onset: 40,000-80,000 mi

Symptoms: Rattling noise from timing area on cold start, Metal shavings in oil, Sudden catastrophic failure with no warning, Check engine light with timing correlation codes, Engine seizes completely

Fix: The plastic balance shaft sprocket deteriorates and allows the gear to slip or the balance shaft bearing to fail, sending metal debris through the entire engine. By the time symptoms appear, internal damage is usually done. Requires complete engine replacement or full rebuild including crankshaft, bearings, pistons, and head work. 25-35 labor hours for engine R&R and rebuild.

Estimated cost: $8,000-15,000

Typical onset: 60,000-100,000 mi

Symptoms: Excessive oil consumption (1 quart per 500-1000 miles), Blue smoke on startup or acceleration, Loss of compression in one or more cylinders, Misfires and rough running, Metal debris in oil

Fix: The M271 EVO pistons have inadequate oil cooling jets and weak ring land design, leading to cracking under normal turbo boost. Once rings fail, metal debris circulates and damages bearings. Requires complete short block replacement or full rebuild with upgraded pistons. 20-30 labor hours.

Estimated cost: $7,000-12,000

Typical onset: 70,000-110,000 mi

Symptoms: Coolant loss with no visible leaks, White smoke from exhaust, Overheating, Rough idle and misfires, Milky oil or coolant in oil

Fix: Head gasket failure often occurs after repeated overheating or as secondary damage from other engine issues. Requires cylinder head removal, resurfacing, and replacement of head bolts. If caught early, 12-16 labor hours. Often discovered during diagnosis of other M271 problems and adds to total rebuild cost.

Estimated cost: $3,500-5,500

Typical onset: 80,000-120,000 mi

Symptoms: Transmission fluid spots under vehicle, Fluid dripping from bell housing area, Low transmission fluid warning, Burnt transmission smell if fluid gets on exhaust

Fix: The cooler lines and connections develop leaks at the crimped fittings or the cooler itself corrodes. Replacement requires raising vehicle and accessing lines along frame rail. 2-4 labor hours depending on which line and whether cooler is also replaced.

Estimated cost: $400-800

Typical onset: 60,000-90,000 mi

Symptoms: Clunking when shifting from park to drive, Excessive vibration at idle, Visible cracks or separation in rubber mount, Transmission sag visible from underneath

Fix: The rear transmission mount degrades and separates, allowing excessive drivetrain movement. Relatively straightforward replacement from underneath. 1.5-2.5 labor hours.

Estimated cost: $300-500

Typical onset: 50,000-80,000 mi

Symptoms: Rough idle and hesitation, Loss of power under acceleration, Hard starting especially when hot, Check engine light with fuel trim codes

Fix: The in-tank fuel filter assembly clogs prematurely, especially with lower-quality fuel. Requires fuel tank drop and filter replacement. Mercedes considers it lifetime but real-world experience shows otherwise. 3-4 labor hours.

Estimated cost: $600-1,000