The PSA XUD is a Diesel engine designed and built by PSA - Peugeot and Citroën. It is an Indirect Injection (IDI) engine, that uses a version of the Ricardo Consulting Engineers Ricardo Comet V prechamber cylinder head design. The engine comes in 1,769 cc 1.8 N/A, 1.8 Turbo, 1,905 cc 1.9 N/A, 1.9 Turbo, 2.1 12 valve N/A and Turbo and was the predecessor to the HDI range of engines. Early HDi Engines were a PSA design, later 16 valve engines were jointly developed with Ford.
The XUD was available with either SOHC 8-valve or 12-valve heads. It was mainly applied transversally in front wheel drive vehicles, tilted by 30°. However, some applications in non-PSA vehicles had the engine installed longitudinally, with rear-wheel drive. The XUD is built in Citroën's plant in Trémery, near Metz.
Displacement ranges between 1,769 and 2,138 cc, and all XU diesel engines have a stroke of either 88 mm (3.5 in) or 92 mm (3.6 in). The former was shared with the XU9. Bore sizes range from 80 mm (3.1 in) to 86 mm (3.4 in), some of which are shared with other XU engines.
Upon its release the engine was noted as one of the best diesel engines (for cars and light vans) in the world with its high power output and refinement it made all other diesel engines seem agricultural. It was also particularly light, with a ready-to-run XUD9 weighing 157 kg (350 lb), 15% less than a comparable diesel of the previous generation. However, if the cooling system is neglected or improperly bled after filling - needing a raised filling level because the expansion tank is not the highest point in the system - the engine has a tendency to blow its head gasket. A simple solution is to use a plastic soft drink bottle with the bottom removed, fitted with a rubber O ring seal on the flange at the cap end for filling. Because radiators (typical life 100,000 miles), generally have only just sufficient cooling capacity when new, in order to help get the engine to operating temperature quickly, silting causes significant problems. Coolant changes to maintain corrosion inhibitors (and stop silting) are critical on this engine. Nonetheless due to the high volume of cars manufactured with this engine spare parts are plentiful and well priced.
Vegetable oil fuel 
The engine, because it is indirect injection, with a slower combustion burn time than direct injection, is suitable to run on SVO (pure vegetable oil). The viscosity of vegetable oil when cold is too great for rotary injection pumps, (in particular the weaker Lucas CAV pump, the Bosch VE fuel pump is superior), preventing it acting as a lubricant and increasing the workload on distributor/rotary injection pump and damaging it. The Lucas EPIC pump fitted to the 2.1 L 12 valve turbodiesel engine after 1995 is the weakest pump of all. Different fresh vegetable oils have different viscosities: thinnest are; sunflower, rapeseed (often only labelled vegetable oil, but with pictures of distinctive yellow flowers), then soya and corn oil, but palm oil (often only marked vegetable oil) is thickest. Vegetable oils thicken when used for cooking, so used oil can be much thicker than any fresh oil. Used oil needs to be very well filtered to avoid filter plugging and/or injection pump damage. Heavily used oil may be highly acidic and corrode the inside of the injection pump. Such oil can only be used as fuel without the risk of damage, if it has been chemically processed into bio-diesel. The open market price for used oil often quite close to special offer supermarket prices for new oil, which can be used straight away. In order to reduce the viscosity of the SVO, it should be heated to engine coolant operating temperature, typically with a two tank system, in order to start and shutdown on diesel or bio-diesel. Versions of this engine from the early '90s onward, are typically fitted with a Peugeot-type coolant heated fuel filter that helps heat fuel and reduce viscosity. Fuel / engine coolant heat exchangers, usually required for straight vegetable oil conversions, are still needed for long term life expectancy, or there will be accelerated wear of the fuel injection pump. Heated vegetable oil is a good injection pump lubricant. This is especially important in cold weather ambient temperatures. Mixing with major oil company brand diesel, to thin the vegetable oil fuel, choosing a thin vegetable oil, or electric heating, or a combination of these are helpful especially when starting and warming up, as coolant heating will not yet be at operating temperature. The difference between the use of good quality fuel and supermarket diesel, in a diesel / vegetable oil fuel mix, will be very noticeable, especially at lower temperatures. The fuel systems used on this engine return heated fuel to the fuel tank. Running with half a tank of fuel will allow the tank to be heated more effectively by this warmed fuel in low ambient temperatures.
The XUD7 has a displacement of 1.8 L (1,769 cc), with a bore of 80 mm (3.1 in) and a stroke of 88 mm (3.5 in). Output is 60 PS (59 hp/44 kW) for the naturally aspirated version or 78 PS (77 hp/57 kW) for the turbocharged model. An intercooled turbocharged version was introduced later, with 90 PS on tap.
|Model||Output||Notes||Model of car|
|XUD7 T/K||78 PS (76 hp/57 kW)||Diesel turbo|
|XUD7 TE||90 PS (88 hp/66 kW)||Diesel turbo with intercooler||Citroen BX TRD/TZD TURBO, Peugeot 405 Turbo, ROVER 200 MK2 TD|
|XUD7/K||60 PS (59 hp/44 kW)||Diesel||Citroën C15D/RD|
|XUD7/Z||60 PS (59 hp/44 kW)||Diesel catalyst|
The XUD9 has a displacement of 1.9 L (1,905 cc), with a bore of 83 mm (3.3 in) and a stroke of 88 mm (3.5 in). Both turbocharged and naturally aspirated versions were produced. Most turbocharged versions feature an intercooler, although a limited number of installations in the Citroën Xantia featured a Turbocharger without intercooler. Both engines also featured either a Bosch or a Lucas mechanical fuel pump and injectors. The original XUD9 engine is known as the "square port" engine, as its cylinder head has square exhaust ports. Later (and noticeably improved) XUD9A engines have oval ports.
|Model||Output||Notes||Model of car|
|XUD9||65 PS (64 hp/47 kW)||Diesel||Peugeot 309 GLD|
|XUD9 A||71 PS (70 hp/52 kW)||Diesel||ROVER 200 MK2 D
|XUD9 TE/L||92 PS (90 hp/67 kW)||Diesel turbo with intercooler||Citroën ZX
|XUD9 SD||63 PS (62 hp/46 kW)||Diesel turbo catalyst||Suzuki Samurai|
|XUD9 SD||75 PS (74 hp/55 kW)||Diesel turbo catalyst||Citroën Xantia
|XUD9 TE/Y||90 PS (88 hp/66 kW)||Diesel turbo with intercooler catalyst|
|XUD9/Z||68 PS (67 hp/49 kW)||Diesel catalyst|
The XUD11 was available in two displacements:
Both were 12-valve SOHC engines with a 92 mm (3.6 in) stroke. The naturally aspirated XUD11 A was bored to 86 mm (3.4 in) for a total displacement of 2.1 L (2,138 cc), while the turbocharged ATE/BTE versions were reduced in bore to 85 mm (3.3 in) for a total of 2,088 cc.
|Model||Output||Notes||Model of car|
|XUD11 A||83 PS (81 hp/61 kW)||Diesel 12-valve SOHC|
|XUD11 ATE||110 PS (108 hp/80 kW)||Diesel 12-valve SOHC turbo||Citroën XM|
|XUD11 BTE||110 PS (108 hp/80 kW)||Diesel 12-valve SOHC turbo catalyst||Peugeot 406|
The engine has been installed into the following vehicles:-
- Pirotte, Marcel (1984-04-19). "Citroën BX 19 TRD". Le Moniteur de l'Automobile (in French) (Brussels, Belgium: Editions Auto-Magazine) 35 (793): 21–23.
||This article includes a list of references, but its sources remain unclear because it has insufficient inline citations. (November 2009)|
- Guide des moteurs Peugeot Citroën (in French)