Mercedes-Benz CL 63 AMG
The last naturally aspirated V12 from Mercedes before the switch to the biturbo era with the M275. The M137 uses SOHC valve actuation with three valves per cylinder — two intake, one exhaust — an architecture Mercedes pursued nowhere else with such consistency. A hydraulic-electric cylinder deactivation system (CDA) was fitted to save fuel; when it fails the CDA valves shut off half the cylinder bank. The same applies to the two encapsulated ignition module banks — completely inseparable, non-repairable, and expensive to replace. A well-maintained M137 delivers one of the smoothest engine notes imaginable: silky, uniform, inaudible at motorway speeds. The price is a maintenance burden that is not for tight budgets.
AMG V12 for a Select Clientele — 26 Units Worldwide
6.3 litres, 444 hp, hand-built in Affalterbach. No turbo, no excuses, just displacement. Only around 26 examples worldwide — anyone who finds one should have it thoroughly inspected. Maintenance costs reflect the rarity.
Engine Weaknesses 6
The hydraulic-electric ZAS cylinder deactivation valves fail with increasing age. Suddenly only 6 cylinders are active, MIL illuminates. Repair costs approx. 880 EUR per valve.
Symptoms: Engine runs rough with strong vibration, significant power loss, check engine light, faults P0307–P0312
The two ignition module banks (one per cylinder bank) fail after 10–15 years — often in quick succession. Fully potted components, not repairable; OEM replacement approx. 1,400 EUR each.
Symptoms: Severe power loss, rough engine, multiple cylinder misfire codes P0300–P0312, fuel smell from exhaust
At high mileage cylinder bore walls become oval, oil enters the combustion chamber. Consequential costs from contaminated lambda sensors and catalytic converters are extremely high.
Symptoms: Blue smoke on start, steadily increasing oil consumption (>0.5 L/1,000 km), contaminated lambda sensors
The oil-water heat exchanger sitting in the V-valley becomes leaky and loses oil at the rear of the engine. Access requires extensive disassembly, so labour costs are high.
Symptoms: Oil spots under the vehicle, oil loss without visible external leak, oil smell after parking
The 12 individual ignition coils on the V12 fail one after another. With 12 cylinders this means frequent workshop visits. Prophylactic replacement of all coils recommended.
Symptoms: Misfires, rough running, check engine light P0301–P0312
M137 V12 is prone to oil loss: valve cover gaskets and sump gasket wear typically. 1–1.5 L oil consumption per 1,000 km is considered acceptable.
Symptoms: Oil smell in engine bay, oil spots under vehicle, dropping oil level.
Vehicle Weaknesses 6
The ABC hydraulic suspension on the C215 is the most expensive weak point. Each axle has a valve block (approximately €1,000 without fitting). Contaminated hydraulic oil damages the proportional valves.
Blocked drainage channels allow water ingress under the glove box. Several control units are located there and suffer permanent damage.
The two valve blocks of the ABC suspension wear through hydraulic contamination. Once the vehicle immediately sags after being switched off, the valve block is defective. Delayed intervention leads to pump and line damage.
On the C215, rust bubbles form preferentially on door lower edges and the C-pillar. Early models up to 2004 particularly affected.
Up to 30 wires in the wiring harness between door and body break through constant flexing after approximately 120,000 km. Window regulators, central locking, seat adjustment and SoftClose on the driver's door are affected.
The NTC interior temperature sensor in the ceiling light housing fails and tells the climate control that the cabin is at 0 °C. The heater then blows maximum hot air permanently.