The PSA XU is a family of internal combustion engines used in Citroën and Peugeot automobiles. It became the dominant mid-size engine in Peugeot and Citroën products through the 1980s and 1990s.

The XU design was introduced in 1981 with the Peugeot 305. It was a SOHC or DOHC straight-4 design with two or four valves per cylinder, using petrol as fuel. It was applied transversely in front wheel drive vehicles only, tilted by 30°. Displacement ranged between 1.6 and 2.0 L (1,580 and 1,998 cc), and all production XU gasoline engines had a bore of 83 or 86 mm (3.27 or 3.39 in). The engine uses an aluminium cylinder head in all models. All models' blocks are made, except XU10, in cast aluminium alloy with removable cast iron wet cylinder liners. XU10 blocks are made in cast iron, with bores machined directly in the block, without removable cylinder liners. Its first Citroën application was on the Citroën BX in 1982, where it appeared in 1.6 L (1,580 cc) format.

The XU was replaced by the more modern EW/DW family.

The XU5 had a displacement of 1.6 L (1,580 cc), with a bore and a stroke of 83 mm × 73 mm (3.27 in × 2.87 in). All XU5 engines were SOHC 2-valve per cylinder designs. They used either a single or double-barrel carburetor, or fuel injection, depending on model. Output ranges from 80–115 PS (59–85 kW; 79–113 hp).

The XU7 had a displacement of 1.8 L (1,762 cc), with a bore and a stroke of 83 mm × 81.4 mm (3.27 in × 3.20 in). All XU7 engines used fuel injection, with a 16-valve DOHC version, the XU7 JP4, also produced. Output ranged from 90–112 PS (66–82 kW; 89–110 hp).

The XU8 had a displacement of 1.8 L (1,775 cc), with a bore and a stroke of 83 mm × 82 mm (3.27 in × 3.23 in).^[1] The only engine in this family is the 16-valve DOHC turbocharged XU8 T which was fitted to the Peugeot 205 Turbo 16.

The XU9 was the predecessor to the XU10 and had an aluminum block with wet iron liners. It had a displacement of 1.9 L (1,905 cc), with a bore and a stroke of 83 mm × 88 mm (3.27 in × 3.46 in). Many versions were produced, from a double-barrel carburetted 8-valve to a 16-valve DOHC fuel injected model. Output ranged from 105–160 PS (77–118 kW; 104–158 hp).

The XU10 has a cast iron block with a displacement of 2.0 L (1,998 cc), with a bore and stroke of 86 mm (3.39 in), making it a square engine. Many versions were produced, from a double-barrel carburetted 8-valve to a 16-valve DOHC, fuel injected, turbocharged model. Output ranged from 115–200 PS (85–147 kW; 113–197 hp).

The XU engine was used in motorsport for over 3 decades.

• PSA XUD (Diesel variant)
• List of PSA engines