Audi S5 4.2 FSI V8 B8

The 4.2 FSI V8 uses direct injection without port injection for valve cleaning, making carbon buildup unavoidable over time. Deposits accumulate on the intake valves and intake ports, restricting airflow and causing misfires, rough idle, and noticeable power loss. Symptoms typically become apparent between 60,000 and 100,000 km, though they worsen gradually. The standard remedy is walnut shell blasting of the intake valves with the intake manifold removed. At a specialist, this costs approximately €600-900 for a V8 (more ports than a 4-cylinder). If left untreated beyond 120,000 km, deposits can become so severe that they affect valve sealing and require more intensive cleaning or even valve replacement, pushing costs toward €1,200. Many specialists recommend carbon cleaning every 40,000-60,000 km as preventive maintenance. Using higher-octane fuel and occasional spirited driving helps slow the buildup but does not prevent it.

The cooling system uses several plastic components that become brittle with heat cycling over time. Common failure points include the coolant expansion tank (cracks at the bottom seam), rear coolant hoses and O-ring fittings at the back of the engine, and the thermostat housing. The thermostat itself can stick open (overcooling, slow cabin heat) or closed (overheating risk). Audi has revised the thermostat housing multiple times, but failures continue on cars older than 8-10 years. A thermostat and housing replacement costs approximately €400-600 at a specialist. If the water pump fails simultaneously (common after 80,000-120,000 km), the combined repair costs €800-1,500 because front-end service position is needed for access. Coolant leaks should be addressed promptly as the V8 is sensitive to overheating.

The S5 uses hydraulic (oil-filled) engine mounts to dampen the V8's vibration. These mounts are under considerable stress from the heavy engine and tend to fail between 80,000 and 130,000 km. When the thin rubber wall tears, oil leaks out and the mount collapses, causing rough idle vibration felt through the steering wheel and floor, clunking when shifting between drive and reverse, and excessive engine movement under load. OEM replacement mounts cost approximately €150-250 each. Labor is intensive as the subframe must be lowered and the engine lifted slightly, pushing total replacement cost for both sides to €400-900 at a specialist. Some owners opt for polyurethane uprated mounts (from 034 Motorsport or similar) which are slightly cheaper and more durable but transmit more vibration to the cabin.

The CAUA 4.2 FSI V8 in the B8 S5 uses an improved timing chain system compared to the earlier B6/B7 generation, which was notorious for catastrophic guide failure. The B8 engine has updated tensioners and metal-reinforced guides, making complete failure rare. However, the hydraulic tensioners can still lose oil pressure overnight after extended use, causing a brief rattle on cold startup lasting 1-3 seconds. This is not immediately dangerous but indicates tensioner wear. If the rattle progressively worsens or exceeds 5 seconds, replacement is advised. The chains are located at the rear of the engine, requiring engine or subframe lowering for access. Parts for a complete timing chain kit cost approximately €800-1,200 and labor is typically 15-20 hours, pushing total cost to €2,500-5,000. Regular oil changes with quality 5W-40 synthetic oil every 10,000 km significantly slow tensioner wear. Most B8 S5 V8 engines reach 150,000+ km without needing chain work if well maintained.

Oil leaks are common on the 4.2 FSI V8 as it ages beyond 80,000 km. The most frequent sources are the oil filter housing gasket at the front of the engine and the valve cover gaskets on both cylinder banks. The oil filter housing uses O-ring seals that harden and crack with heat cycling. Valve cover gaskets similarly deteriorate. Because oil can travel along engine surfaces, diagnosis requires careful inspection to identify the true source. Oil filter housing seal replacement costs approximately €300-500 (seals are inexpensive but labor is 3-4 hours). Valve cover gaskets cost €400-700 per side at a specialist. If both sides need attention simultaneously, combined costs can reach €1,000. These leaks are primarily a nuisance rather than a safety issue, but left unchecked they can contaminate other components and create smoke from oil dripping onto hot exhaust surfaces.

The 6-speed manual S5 has a well-documented clutch durability issue. The standard clutch struggles to handle the V8's 440 Nm of torque over extended use, particularly with spirited driving or launch starts. Many owners report clutch slippage beginning between 50,000 and 80,000 km, well below what might be expected. Clutch replacement is labor-intensive because the transmission and transfer case must be removed. Parts (clutch kit plus dual-mass flywheel) cost approximately €600-1,000, and labor runs 8-12 hours, bringing total cost to €1,500-2,800 depending on whether the flywheel is replaced. The Tiptronic automatic (ZF 6HP28) is considered very reliable and does not share this issue. When buying a manual S5, checking for clutch slip under load in higher gears is essential.

The B8 platform uses a complex multi-link front suspension with multiple control arms per side. The rubber bushings in these arms deteriorate with the extra weight of the V8 engine, typically showing wear between 70,000 and 110,000 km. Symptoms include steering wheel vibration at highway speeds (often between 100-120 km/h), vague steering feel, and uneven tire wear. Audi does not sell replacement bushings separately; the entire control arm must be replaced. A full set of front control arms (upper and lower, both sides) costs approximately €400-700 for aftermarket parts or €600-1,000 for OEM. Labor adds €200-400. Uprated control arm kits from specialists (such as 034 Motorsport or Meyle HD) use harder rubber or polyurethane bushings that last longer.

The direct injection system uses two high-pressure mechanical fuel pumps driven by camshaft lobes. The N276 solenoid in each pump regulates fuel pressure and can wear over high mileage. Symptoms include EPC warning light, fault code P0088 (fuel pressure too high), misfires, and in severe cases, engine shutdown. The solenoid is not available separately from Audi, requiring full pump replacement at approximately €600-800 per pump plus labor. Aftermarket upgraded HPFP kits exist that reduce solenoid duty cycle and extend life. This issue is relatively uncommon and typically only appears beyond 150,000 km, but when it occurs it can leave the car stranded.