The first-generation Peugeot 508 (internal code name W2, 8D for the sedan, 8E for the SW estate) had the challenging task of simultaneously replacing the 407 and 607. It marked a significant move upmarket for Peugeot with a refined finish, excellent sound insulation, and imperial road handling, true to the brand's reputation (double wishbone front suspension on GT versions, pseudo-MacPherson on others). Restyled in 2014, it modernized its front end and updated its engines to meet Euro 6 standards. While its road qualities are undeniable, its overall reliability was heavily tarnished by the misfortunes of the first-generation "Prince" petrol engines (1.6 THP) and, later, by the BlueHDi diesel emission control systems.
The Peugeot 508 I is an excellent road car, but its reliability record is very mixed depending on the engine chosen. If you are looking for a petrol engine, absolutely avoid the 1.6 THP 156 hp and the 1.6 VTi 120 hp, whose timing chain failures and oil consumption issues can ruin your budget. You must opt for a restyled version equipped with the 1.6 THP 165 hp, which is infinitely more reliable and very pleasant to drive. For diesel, the older 2.0 HDi (140/163) are monsters of robustness. The more recent BlueHDi versions are mechanically excellent but require budgeting for the inevitable AdBlue tank replacement. Avoid the BMP6/ETG6 automated manual gearboxes in favor of manual or EAT6 automatic gearboxes.