BMW M21 Six Cylinder Diesel Engines

BMW M21 diesel engine

M21 in an E30 324d.


BMW had begun research into diesels in 1975 in co-operation with Steyr-Puch. The resultant M21 was BMW's first diesel in a production car. It was launched in 1983 in the E28 five series and was later sold in the 1987 E30 three series. It was available with or without a turbocharger.

It was used in the E34 five series until the introduction of the more modern M51 diesel in 1991.

Several American cars used the M21 including the Vixen motor home and the Lincoln Continental but it was never sold in the UK.

BMW M21 diesel engine

M21 turbo diesel.


BMW's goal was to build a diesel with the smoothness and power delivery of a petrol engine. Along with Steyr-Puch the M105 prototype was developed in 1978 to these ends using the petrol M20 as a basis. The 1983 production M21 was the result.

Compared to the M20 the M21 had strengthened conrods and a strong forged crankshaft with larger diameter bearings. The block was 10mm taller due to the size of the pistons.

Diesel injection was performed by a distributor pump, a much smaller choice than the then common in-line pumps. Originally all M21s had a turbo, but in 1986 a normally aspirated version was made available, it also lacked an oil cooler.

In 1987 BMW installed DDE, Digital Diesel Electronics, to control the injection pump on the turbo version of the engine (1989 for the non-turbo). In a futuristic move BMW linked this to a fly-by-wire throttle. The result was more torque and lower emissions.

BMW M21 diesel engine

M21 in an E34 524td.


Code Size Power
Made Bore x
Timing Weight
VANOS Used in
M21 2.4
2.4 Turbo
86 @ 4600
115 @ 4800
112 @ 2500
155 @ 2400
85 - 86
83 - 91
80x81 Belt 126 No E30 324td,


BMW M21 diesel engine

Brand new M21 in an E30.


This engine has a timing belt, be sure to check it.

An older diesel like this has fewer emissions devices and is less likely to coke up as a result.

It also has a more frequent oil change cycle than newer engines, if this is followed it can only be good for the life of the turbo.