Peugeot 508 1.6 THP Mk1

The EP6 engine's timing chain is well documented as a weak point. The hydraulic chain tensioner has a release valve that weakens over time, allowing oil pressure to bleed off overnight. On cold start, the slack chain rattles against its guides for anything from a few seconds to 30 seconds until oil pressure builds. Typically appears between 60,000 and 120,000 km. If ignored, the chain can skip teeth and cause piston-to-valve contact, destroying the engine. PSA revised the tensioner part number multiple times. The post-2014 EP6FDT 165 hp engine has an improved chain and tensioner, reducing but not eliminating the issue. Repair involves replacing chain, guides, tensioner, and sprockets. At an independent specialist, expect around 6-8 hours of labor. Total cost typically falls between €800 and €1,500 at an independent shop, rising to €1,800-2,200 at a Peugeot dealer.

The HPFP is a known weakness on THP engines across all PSA models using this engine. Symptoms include engine hesitation under load, difficulty starting (especially when hot), and fault code P0087 (low fuel rail pressure). Most failures occur between 60,000 and 120,000 km. Peugeot previously offered goodwill contributions on cars under 6 years old with fewer than 100,000 km, but this is unlikely to apply to any remaining 508 Mk1. Specialist HPFP refurbishment services exist and can save significant money compared to full replacement. A refurbished pump costs around €400-600, while a new OEM pump with fitting at a dealer runs €1,200-1,500.

All direct-injection petrol engines suffer from carbon buildup, but the EP6 THP is particularly prone to it. Because fuel is injected directly into the combustion chamber, there is no fuel wash over the intake valves to keep them clean. Oil vapour from the PCV system bakes onto the valve stems and ports. Symptoms include rough idle, hesitation during acceleration, cold-start misfires, and a gradual loss of power. Specialists recommend walnut-blasting the intake valves every 50,000-60,000 km. This cleaning is not detectable via OBD diagnostics. At a specialist, walnut blasting costs €400-600. Some owners report a dealer quote of up to €800. The engine can lose as much as 20% of its power from carbon buildup.

The factory turbo oil feed pipe uses an O-ring that degrades from repeated heat cycles. Once it starts leaking, oil drips onto the hot turbo and exhaust, causing smoke and burning smell. If left unattended, oil starvation can damage the turbo bearings, turning a €300 pipe repair into a €1,200+ turbo replacement. Upgraded aftermarket braided stainless steel oil lines are available for around €80-120 and are more durable than the original. Peugeot later made a heat shield available as a retrofit. The pipe itself is relatively accessible, so labor is 1-2 hours. Catching this early keeps repair costs low.

The 508 Mk1 shares its electronic parking brake system with several PSA models, and it is a known weak point. The electric motor integrated into the rear brake caliper can fail, typically manifesting as a 'Parking brake fault' warning on the dashboard. The car may be unable to engage or release the parking brake. Causes range from a simple blown 20A fuse (essentially free to fix) to a failed caliper motor requiring replacement. A new caliper with integrated EPB motor costs €250-400 per side. Diagnosis fees are typically €50-80. Total repair at an independent shop is usually €300-500 per side.

PSA considers up to 1 litre per 5,000 km as acceptable oil consumption on the EP6 THP. Many owners report consumption exceeding this, sometimes reaching 1 litre per 1,000-2,000 km. At moderate levels (1L/3,000-5,000 km), regular top-ups are needed between services. At extreme levels, the cause is usually worn piston rings or valve stem seals. A defective PCV valve can also route excessive oil vapour into the intake. PCV valve replacement is inexpensive (€50-150 with labor). Piston ring or valve seal repair requires significant engine work, costing €1,500-2,500. Regular oil level checks between services are essential.

The EP6 engine uses a plastic thermostat housing that becomes brittle over time and can crack, leading to coolant leaks and overheating. The electric water pump can also fail, typically between 80,000 and 130,000 km. Symptoms include a coolant warning light, poor cabin heating, or visible coolant puddles underneath. The plastic coolant pipe running from the thermostat to the water pump is difficult to access and prone to breaking during removal. Parts cost €200-400 depending on whether both thermostat and water pump need replacing, with 4-6 hours of labor due to poor accessibility.