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BMW E28 engine 2 16.09 JM.jpg
ManufacturerBMW Motoren GmbH Steyr
Displacement2.4 L (2,443 cc)
Cylinder bore80 mm (3.15 in)
Piston stroke81 mm (3.19 in)
Block materialCast iron
ValvetrainSOHC 2 valves x cyl.
Compression ratio22.0:1
Operating principleDiesel
TurbochargerGarrett T03 ('td' versions),
None ('d' versions)
Fuel systemSwirl chamber injection, distributor fuel injection pump
Fuel typeDiesel fuel 45 CN (DIN 51601)
Cooling systemWater-cooled
Power output63–85 kW (84–114 hp)
Torque output152–220 N⋅m (112–162 lb⋅ft)

The BMW M21 is a straight-six diesel engine developed by the Bavarian engine manufacturer BMW. It has swirl chamber injection and is based on the M20 petrol engine[1] and was produced for BMW by the Upper Austrian Steyr engine plant from 1983 to 1991. It was succeeded by the M51.[2]


In the 1970s BMW decided to develop an engine, which would both be powerful and have a good fuel economy. This was caused by the oil crisis in 1973. In 1975 a group of BMW engineers started working on the M21 diesel engine, the M20 petrol engine was used as the basis. The Steyr engine plant was planned from the beginning to be the sole manufacturer of the new diesel engine. It started as a joint venture with Steyr-Daimler Puch in 1978, but in February 1982 BMW took over the reins.[3] The first engines built there (in early 1982) were six-cylinder petrol units. Beginning in 1983, Ford was planning to buy 190,000 BMW turbodiesels over a period of several years.[3] With the American diesel market imploding in the early 1980s, Ford only built a small number of Lincolns thus equipped and only for two model years.

In 1983 at the IAA, the first passenger car was shown to the public which made use of the 85 kW (115 PS) M21.[4] It was the E28 524td, which has a top speed of 180 km/h (110 mph) and reaches 100 km/h (62 mph) in 12.9 s. This 5-series BMW was the fastest series production diesel car in the world in 1983. It has a fuel economy of 7.1 L/100 km (40 mpg‑imp; 33 mpg‑US).[2]

Technical description[edit]

As per the M20, the M21 is water-cooled,[5] has a cast iron block and a SOHC valvetrain. The camshaft is driven by a belt,[2] each cylinder has one inlet and one outlet valve.[1] Compared to the M20, the M21 has reinforced connecting rods, cylinder heads, pistons, valves[2] and a reinforced crankshaft[1] with seven[5] bearings.

For faster engine startup the M21 has a glowplug system called instant start, which reduces the time to reach starting temperature compared to similar diesel engines.[2] The fuel is injected into swirl chambers.[1]

A Garrett turbocharger[4] is used (without an intercooler). Initially, the M21 was only available as a turbocharged engine. In 1985, BMW introduced a naturally aspirated version of the M21, which was popular in countries with a high motor vehicle tax.[2]

Initially, the fuel pump was controlled mechanically. From 1987, an electronically controlled fuel pump was used,[6][7] which increased the torque output by 10 N⋅m (7 lb⋅ft). The updated engine has a smaller turbocharger, which improves response.[1]


Engine Aspiration Power Torque Redline Year
M21D24[8][5] Turbo-diesel 85 kW (115 PS; 113 hp)
at 4800 rpm
210 N⋅m (155 lb⋅ft)
at 2400 rpm
5350 rpm 1983
220 N⋅m (162 lb⋅ft)
at 2400 rpm
Natural 63 kW (86 PS; 85 hp)
at 4600 rpm
152 N⋅m (112 lb⋅ft)
at 2500 rpm
5150 rpm 1985


See also[edit]


  1. ^ a b c d e Andreas in Bimmer: Die BMW-Sportdiesel: Von 524td E28 über 530d E39 bis BMW M550d F10, published at 21 January 2012, retrieved at 9 April 2015. (german)
  2. ^ a b c d e f Ronan Glon in 30 years ago: BMW introduces its first diesel engine, published at the 22nd of Juli 2013, retrieved at 9 April 2015.
  3. ^ a b Hutton, Ray, ed. (5 June 1982). "BMW's Austrian outlet opens". Autocar. Vol. 156, no. 4459. IPC Business Press Ltd. p. 12.
  4. ^ a b Auto Motor und Sport: Der zweite 5er von BMW: Die Baureihe E28 Der unscheinbare Revoluzzer, retrieved at 9 April 2015. (german)
  5. ^ a b c "BMW M21 D24 (246TB)". Meyer Motoren (in German). Archived from the original on 30 June 2016.
  6. ^ BMW M21 engine page Archived 2019-05-17 at the Wayback Machine. Retrieved at 9 May 2016.
  7. ^ E30 Zone- M21. Retrieved at 3 January 2017.
  8. ^ "BMW 5 Series (E28) specs & photos - 1981, 1982, 1983, 1984, 1985, 1986, 1987, 1988". Retrieved 12 August 2021.
  9. ^ a b Turbo Diesel Lincoln Continental M21. Retrieved at 3 January 2017.
  10. ^ Tutu, Andrei (3 September 2014). "Meet the Vixen RV, BMW 2 Series Active Tourer's American Ancestor". Retrieved 2 January 2021.