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BMW M21D24 engin PL.JPG
Manufacturer BMW
Production 1983–1991
Configuration Inline-6
Displacement 2,443 cc (149 cu in)
Cylinder bore 80 mm
Piston stroke 81 mm
Cylinder block alloy Cast iron
Valvetrain OHC
Compression ratio 22:1
Turbocharger Garrett (85 kW engines only)
Fuel system indirect) fuel injection
Fuel type Diesel fuel
Cooling system Water-cooled
Power output 63 – 85 kW
Torque output 152 – 220 Nm
Predecessor None
Successor M51

The BMW M21 is a six-cylinder-inline-diesel engine developed by the Bavarian engine manufacturer BMW. It uses (indirect) fuel 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. In 1983 at the IAA, the first passenger car was shown to the public which made use of the 85 kW M21. It was the E28 524td, which has a top speed of 180 km/h and reaches 100 km/h in 12,9 s. This 5er-BMW was the fastest series production diesel car in the world back in 1983. It has a fuel economy of 7,1 l /100 km.[2]

Technical description[edit]

As per the M20, the M21 is water-cooled,[3] 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[3] 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,[5][6] 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[3] turbo 85 kW (114 hp)
@ 4800 rpm
210 N⋅m (155 lb⋅ft)
@ 2400 rpm
5350 rpm 1983
220 N⋅m (162 lb⋅ft)
@ 2400 rpm
5350 rpm 1987
natural 63 kW (84 hp)
@ 4600 rpm
152 N⋅m (112 lb⋅ft)
@ 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 the 21st of January 2012, retrieved at the 9th of 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 the 9th of April 2015.
  3. ^ a b c Meyer Motoren: BMW M21. Retrieved at the 9th of May 2016. (german)
  4. ^ Auto Motor und Sport: Der zweite 5er von BMW: Die Baureihe E28 Der unscheinbare Revoluzzer, retrieved at the 9th of April 2015. (german)
  5. ^ BMW M21 engine page. Retrieved at the 9th of May 2016.
  6. ^ E30 Zone- M21. Retrieved at the 3rd of January 2017.
  7. ^ a b Turbo Diesel Lincoln Continental M21. Retrieved at the 3rd of January 2017.
  8. ^ Meet the Vixen RV, BMW 2 Series Active Tourer’s American Ancestor. Retrieved at the 3rd of January 2017.

External links[edit]