Mercedes-Benz S 500
4.7-litre BiTurbo V8 with direct injection (CGI), 90-degree bank angle and hot-V layout — turbos sit between the cylinder banks. Timing chain and tensioners are the first thing to check on used examples: cold-start rattle is a warning sign. Alusil bores react badly to wrong oil or extended intervals; piston slap develops gradually from oil film loss, often triggered by fuel-washing injectors. Ignition coils rarely last beyond 120,000 km. The oil separator should be checked after 100,000 km — when faulty it forces oil vapour into the intake and accelerates intake valve carbon build-up. Sound character: subtle BiTurbo rumble, no naturally aspirated roar. Shorten maintenance intervals to 10,000 km, oil MB 229.5 with low Noack value. Engine long-lived with correct maintenance — problem cars are almost always those with missed oil changes.
Grand Tourer V8 BiTurbo — Finest M278 Experience
The S-Class Coupé is what the CL always wanted to be: long, wide, low, and fitted with a V8 that loses its composure when provoked. Acoustically more present than the saloon — the lower roofline reflects the sound better. At 200 km/h it feels like 120. The pillarless construction without a B-pillar gives the cabin a sense of space no SUV can offer. Rarer than the saloon, with rising collector value. One of the last great V8 grand tourers.
Engine Weaknesses 9
All M278 built before Feb. 2013 are affected by prematurely wearing chain tensioners. Mercedes responded with a goodwill campaign: new tensioners plus a check valve in the cylinder head.
Symptoms: Metallic rattle on cold start (2–5 seconds), later also rattling when warm and on hot restart
No M278 with over 120,000 km known without cylinder bore damage. Silitec coating is sensitive to knock. Full rebuild approximately €14,000–18,000, replacement engine approximately €20,500.
Symptoms: Increased oil consumption (1–1.6 L/1,000 km), engine knock, rough idle, brass swarf in oil
The M278 is the best-known example of Mercedes' oil migration problem. Oil seeps from the camshaft adjuster solenoid capillary-style through the entire engine wiring harness to the ECU. Costs up to €11,000 if ECU and harness both need replacing.
Symptoms: Cold-start rattle, fault codes P0010/P0011 camshaft adjuster, oil traces on connectors, sporadic engine misfires, complete ECU failure
CGI direct injectors carbon up from 120,000 km and dribble after shutdown. Post-drip washes the oil film from the bore — a direct precursor to bore damage.
Symptoms: Rough idle, fuel smell after shutdown, black wet spark plugs on individual cylinders, high consumption, misfire fault codes
The wastegate linkage bush wears and initially causes rattling on cold start that develops into a permanent noise.
Symptoms: Metallic rattle from the turbo area on cold start, sluggish acceleration, P0299 boost pressure fault code
The hydraulic engine mounts on the M278 V8 lose their damping fluid after around 100,000 km. The heavy V8 (>250 kg) then causes noticeable vibrations throughout the vehicle.
Symptoms: Vibrations at idle in the cabin, clunking on throttle application and lift-off, visibly collapsed engine mount
Ignition coils fail from around 100,000 km — usually one at a time, rarely all together. Misfires on individual cylinders, MIL flashes. Left untreated, fouled plugs wash the oil film from the bore.
Symptoms: Stumble at idle and part throttle, flashing engine warning light, misfire fault codes (cylinders 5 and 7 most commonly affected), occasional fuel smell
The oil separator (crankcase ventilation) wears and feeds too much oil vapour into the intake. Accelerates intake valve carbon build-up and measurably increases oil consumption.
Symptoms: Increased oil consumption, blue smoke on cold start, oil film visible in intake pipe, smoke from exhaust after extended parking
As a pure direct-injection engine, the M278 builds up carbon deposits on the intake valves. Walnut blasting every 60,000 km is recommended.
Symptoms: Rough idle, slight power reduction, occasional misfires when cold
Vehicle Weaknesses 16
The active electro-hydraulic ABC suspension requires intensive maintenance. Hydraulic lines, valve blocks and pumps can develop leaks. Hydraulic oil change required every 50,000 km.
Air bags and pressure hoses develop leaks. The compressor runs continuously and overheats. Repair: air bag pair 2,500–3,500 €, compressor 1,000–1,300 €.
Air struts on Airmatic and Magic Body Control suspensions develop leaks. Vehicle drops, suspension warning light appears. Repair per corner is very costly.
The hydraulic Magic Body Control suspension is prone to valve block and hydraulic pump failures. Contamination in the oil causes system failures.
The COMAND infotainment system freezes sporadically or fails completely. System faults increase from around 100,000 km.
Radar and camera sensors for adaptive cruise control and emergency braking can cause malfunctions due to dirt or defects. Calibration after repair is expensive.
The COMAND navigation system shows read errors, freezes or fails to boot. A defective drive unit is the most common cause.
Panoramic roof drainage channels become dirty, rubber seals become brittle through UV radiation. Result: water ingress into the interior, particularly in the rear area.
Matrix LED headlights are not repairable -- individual modules cannot be replaced. Moisture and electronic failures require complete headlight replacement.
Window regulators fail or become unresponsive. Cause is often a software fault in the door control unit, fixable by update.
Brake discs and pads wear quickly due to the high vehicle weight. Particularly during spirited driving.
Frameless door windows are inherently harder to seal. Worn seals or minimal window misalignment cause wind whistling from around 80 km/h.
The pneumatic control unit operates soft-close, central locking and rear headrests via a shared pump. Leaks cause all functions to fail simultaneously.
The Comand NTG5 infotainment system shows display failures, freezing and navigation start errors. Temperature-dependent malfunctions occur frequently.
Seat heating mats and massage pneumatics in the multicontour seats are wear items. Heating mats fail internally, the PSE pump loses pressure for the massage function.
The rubber seal of the Keyless Go microswitch in door handles becomes brittle through UV and temperature cycling. Moisture enters, the switch corrodes.