The BMW M51 is an inline-6 cylinder Diesel engine produced by the Upper Austrian BMW plant in Steyr from July 1991 through February 2000. Its predecessor is the BMW M21; the successor is the BMW M57.
Description
The M51 is a water-cooled and turbocharged inline six-cylinder diesel engine. It is an indirect injection design with fuel is supplied by and electronically - controlled Bosch VP37 distribution injection pump. The displacement is 2,497 cc (152.4 cu in) and the compression ratio is 22.0:1.
Some engine variants have an intercooler in addition to the turbocharger; vehicles so equipped can be identified by the designation tds. The M51 has a cast iron block and aluminum head, one chain driven overhead camshaft, and two valves per cylinder. Compared to the M21 the M51 features tappets and hydraulic valve lash adjustment. The fuel injection in the first engines and all E36 models is controlled by the Bosch DDE 2.1, which was replaced after the first technical revision by DDE 2.2, resulting in greater torque at lower revs. For lubrication, BMW originally approved a range of oil viscosities depending on the climate and ambient temperature, such was 10w-40 or 15w-40,l though 5w-40 synthetic oil is commonly used as modern replacement.
Version Power Torque Years M51D25 UL at 4800 rpm at 1900 rpm 1991–1997 M51D25 OL at 4800 rpm at 2200 rpm 1991–1996 Opel X25DT at 4800 rpm at 1400 rpm 1994–2001 M51D25TÜ UL at 4800 rpm at 1900 rpm 1996–1998 M51D25TÜ OL at 4800 rpm at 2200 rpm 1996–1998 M51D25TÜ OL at 4600 rpm 1998–2000 M51D25M1 at 4400 rpm at 2300 rpm 1995-2001
Applications: 1991 - 1996 BMW 325td (M51D25 UL) 1996 - 1998 BMW 325td (M51D25TÜ UL) 1993 - 1996 BMW 325tds (M51D25 OL) 1996 - 1998 BMW 325tds (M51D25TÜ OL) 1992 - 1996 BMW 525td (M51D25 UL) 1991 - 1996 BMW 525tds (M51D25 OL) 1996 - 2000 BMW 525tds (M51D25TÜ OL) 1996 - 2000 BMW 525td (M51D25TÜ UL) 1996 - 2000 BMW 725tds (M51D25TÜ OL) 1995 - 2001 Range Rover (P38A) 1994 - 2001 Opel Omega B 1992 UMM Alter II (single example; engine, gearbox, and electronics were fitted by BMW in Munich)
See also List of BMW engines
References
Die BMW-Sportdiesel: Von 524td E28 über 530d E39 bis BMW M550d F10 (german) Opel Omega B 2.5 TD 96 kW 130 PS - Motor: 25DT, X25DT, X25TD - Eco Optimierung / Leistungssteigerung (german) Etzold: So wird's gemacht: pflegen – warten – reparieren. Band 102, BMW 5er E39 Delius Klasing Verlag. Pages 12 and 13 (german) BMW E38 7 Series 725 tds Technical data Übersicht der Motorölqualitäten. Page 7 (german) Automobile Catalogue: 1997 Range Rover 2.5 DSE (model for Europe ) specifications & performance data review .