Mercedes-Benz CL 65 AMG
Twelve cylinders, two turbochargers, a V-valley layout — technically fascinating and maintenance-intensive in equal measure. The fully encapsulated ignition module system with two banks at 1,400 EUR each is the most well-known cost factor; failure of both banks usually follows in quick succession. The oil-water heat exchanger in the V-valley almost always leaks eventually — factor in engine removal for the repair. The four camshaft solenoids fail to seal reliably after 80,000–100,000 km; oil creeps into the wiring harness and corrodes control units. Both turbochargers sit deep under the engine bay — removal and installation costs more than the turbo itself. Runs without issue beyond 300,000 km with diligent maintenance; what kills it is deferred servicing. Purchase requirement: complete service history, documented wiring harness check, no ABC alarm backlog, fresh ignition modules.
612 hp GT — When Excess Becomes Principle
The CL 65 AMG is the most audacious car from Stuttgart: 612 hp in a 2.25-tonne GT, 4.4 seconds to 100. The torque is limited to 1,000 Nm because the gearbox otherwise wouldn't survive. On long straights a different calibre from any V8 equivalent. Hand-built engine from Affalterbach with a name plate on the cam cover. Fuel consumption: double digits before the decimal point is the permanent state.
Engine Weaknesses 9
Both ignition module banks are fully potted wear items with a typical service life of 10–15 years. Failures tend to follow each other quickly. OEM cost approximately €1,400 each.
Symptoms: Jerking and power loss, rough running, misfire codes P0307–P0312, petrol smell from the exhaust
The two turbochargers show bearing and wastegate wear at high mileage. Engine removal is required for replacement; repair costs €2,000–4,000 per turbo.
Symptoms: Whistling or rattling turbo noises, power loss under hard acceleration, blue smoke from oil loss
The M275 V12 Biturbo in the S600/CL600 puts extreme stress on the engine mounts due to its weight (>300 kg engine). At the same time, the ABC hydraulic lines age and leak. Both issues frequently occur together.
Symptoms: ABC suspension hydraulic oil loss, engine sitting lower, vibrations in the cabin, ABC warning message
On the M275 V12 with 4 camshafts, all 4 solenoids are affected. Oil leaking into the wiring harness leads to ECU corrosion. Repair is especially labour-intensive on the V12.
Symptoms: Cold-start rattle, camshaft adjuster fault codes bank 1+2, oil traces on connectors, in extreme cases engine ECU failure
Wiring harness insulation in the engine bay becomes brittle after 10–15 years from heat. Affected: injector, MAF and throttle body wiring. Short circuits in the MAF harness can destroy the engine beyond repair.
Symptoms: Sporadic misfires, MAF fault codes, ignition misfires without clear cause, in extreme cases engine failure and fire risk.
The integrated contact plate (TCM) in the 7G-Tronic fails due to heat damage at the speed sensors. Gearbox shifts jerkily, then not at all. New plate requires SCN coding at an authorised dealer.
Symptoms: Delayed, jerky gear changes, gearbox stuck in 2nd gear (limp mode), fault codes P0717/P0718 transmission control unit.
The oil-water heat exchanger seal in the V-valley becomes leaky. Engine removal is required for repair, so total costs reach €1,700–2,500 despite the cheap parts.
Symptoms: Oil loss without a clearly visible leak, oil spots after extended parking, occasionally oil in the coolant reservoir
The separate intercooler cooling circuit loses coolant through ageing hoses and O-rings. Retrofit fix: the M279 expansion tank fits as a direct swap.
Symptoms: Dropping coolant level in the expansion tank, overheating warning on extended motorway runs, power reduction
Valve stem seals harden and piston rings wear with increasing mileage. 12 cylinders mean 48 valve stem seals. Oil consumption rises noticeably from 150,000 km — up to 1 L/2,000 km.
Symptoms: Blue smoke after prolonged idle, dropping oil level between service intervals, carbon deposits on spark plugs.
Vehicle Weaknesses 6
On the C216 with ABC suspension, replacing all dampers and valve blocks costs €8,000–10,000. Airmatic is also expensive: two air bags cost around €2,500, the compressor another €600.
Blocked drainage channels allow water in under the glove box, damaging the control units housed there. Diagnosis is difficult as faults often appear only intermittently.
The Active Body Control suspension is very maintenance-intensive. Hydraulic lines become porous and contaminate the system. Valve block and hydraulic pump fail regularly.
Control units located under the glovebox can suffer total failure from water ingress. Gearbox loses communication with ABS.
The instrument cluster suffers pixel failures, display drop-outs and incorrect gauge positions. In the worst case the immobiliser activates.
On the C216, a weak or defective auxiliary battery triggers a cascade of electrical faults: speedo flickers, gearbox and ABS lose communication, radio fails, central locking fails.