Audi S8
Biturbo V8 with 309 kW for S6/S7 C7 and S8 D4. Detuned version of the RS V8 with cylinder deactivation. Comfortable and powerful at the same time.
520 hp sleeper — retiree sedan, supercar thrust
Twin-turbo V8 in stealth mode — looks like a retiree's sedan, hits like a freight train at full throttle. Better power-to-weight than a 911 Carrera 4S. Cold start loud enough to set off car alarms. A bargain used, as long as air suspension and turbo lines hold up.
Engine Weaknesses 10
KBA recall (code 21H7) for S6 and RS6 built June 2012 to March 2017: the too-fine oil strainer restricts turbocharger lubrication. Replacement with a coarser-mesh strainer required. Without repair, turbo damage can result.
Symptoms: Power loss, whistling turbo noise, engine check light; in advanced cases metallic swarf in oil
At high mileages (150,000–200,000 km) 4.0 TFSI engines show timing chain stretch, recognisable by camshaft synchronisation faults. Repair requires extensive engine work on the V8.
Symptoms: Idle fluctuations, camshaft synchronisation fault codes, rattling on cold start from the front timing drive
The high-pressure fuel pump on the 4.0 TFSI is a known wear component. Pressure loss causes injection problems and uneven combustion. Wear increases with long service intervals or poor fuel quality.
Symptoms: Rough running, injection noise, power loss at high rpm, cold-start problems
Aluminium-silicon alloy cylinder walls are hard to repair once worn. Elevated oil consumption from piston ring wear occurs, especially with spirited driving and long intervals.
Symptoms: Steadily dropping oil level, slightly bluish smoke under acceleration, oil consumption above 1 litre per 1,000 km
A failed crankcase ventilation (PCV) routes engine oil into the intake channels. Unburnt oil entering the cylinders increases oil consumption and can cause knocking and power loss.
Symptoms: Blue smoke from exhaust, significantly elevated oil consumption, power loss, oily intake tract on inspection
The 4.0 TFSI cooling system relies on an electric main water pump (079121014M) and an auxiliary pump. Plastic housings and thermostat housing become porous with age. Failure creates overheating risk.
Symptoms: Coolant temperature rises unusually quickly or stays permanently low, coolant loss without visible leak, heater not working efficiently
The ZF8HP automatic transmission suffers from worn shift solenoids and torque converter when transmission fluid changes are missed. Shift jerk and overrun on gear changes are typical.
Symptoms: Jerk when pulling away or shifting, shift pauses in sport mode, in severe cases transmission limp mode, mechatronics fault codes
The hot-V architecture places turbos and spark plugs in the thermally extreme engine valley. Spark plug wear increases from around 40,000 km; CoD-deactivated cylinders (2, 3, 5, 8) are especially affected.
Symptoms: Misfires especially at CoD cylinders, stumbling at partial load, engine check light, misfire fault code
The vibration-damping engine mounts on the V8 suffer increased wear from torque impulses. According to used-car reports they typically need replacement from 50,000 km.
Symptoms: Vibrations in the passenger compartment under acceleration, audible movement when blipping and releasing the throttle, shift jerk at full load
The four lambda sensors (pre- and post-cat per bank) are exposed to extreme heat stress in the hot engine valley. Pre-cat sensors fail more often, causing rich mixture and elevated consumption.
Symptoms: Engine check light, increased fuel consumption, power loss, fault codes P0130–P0167 (mixture control)
Vehicle Weaknesses 7
The optional carbon-ceramic brakes on the S8 D4 are extremely susceptible to stone chip damage and thermal shock fractures. A faulty disc can cost up to €5,000.
The AAS air suspension on the S8 D4 is a well-known money pit. Compressor (~€360 parts), air bellows (€350–900 each) and level sensors all fail from 100,000–150,000 km.
The MMI 3G(+) system in the S8 D4 fails due to moisture or voltage spikes. Dealer charges €2,000–4,500; a specialist repair costs around €300–650.
The ZF 8HP automatic in the S8 D4 needs an oil change every 60,000 km. Neglected changes lead to shift irregularities and premature wear.
Due to the high weight (~2,000 kg) and engine output, brake pads and discs wear heavily. Complete front-and-rear brake replacement costs €1,000–3,000.
Suspension bolts, wishbone bushes and brake carriers corrode when underbody protection is neglected, particularly on salted roads.
The S8 D4's highly complex electrical system is sensitive to voltage fluctuations. Battery failure triggers control unit errors. Workshop costs €200–600.
Reports & Tests
31 owner complaints filed with NHTSA (2012–2018). Most reported: Engine (18), Other (4), Powertrain (3).