Engine code
The M21 is a 2.4 liter straight-six diesel that Wikipedia says was built for BMW by the Steyr plant in Austria from 1983 to 1991. It is based on the M20 petrol engine and was succeeded by the M51.
BMW sold the M21 in one US-market model, the E28 524td, built 04/1983-12/1985. BMW's parts data lists the other M21 cars, the E28 524d, the E30 324d and 324td, and the E34 524td, only in rows outside the US catalog.
Quick read
- Ownership position: Not established yet. We are still researching this engine.
- Reliability: Not established yet. We are still researching this engine.
- Cost to own: Not established yet. We are still researching this engine.
- Power potential: Not established yet. We are still researching this engine. The factory output Wikipedia lists is in Technical Specifications.
- Main watch item: Not established yet. We are still researching this engine.
M21 At a Glance
| Question | Practical answer |
|---|---|
| Sold in US-market BMWs | Yes, in one model. BMW's US parts data lists the M21 only in the E28 524td. |
| Years built | Wikipedia says 1983-1991 worldwide. The US E28 524td in BMW's parts data was built 04/1983-12/1985. |
| Layout | SOHC straight-six diesel with a cast iron block, two valves per cylinder and a belt-driven camshaft, according to Wikipedia. |
| Displacement | 2,443 cc, 80 x 81 mm, 22.0:1 compression |
| Induction and injection | Garrett T03 turbocharger on the td versions, swirl chamber injection and a distributor fuel injection pump |
| Factory output | Wikipedia lists the turbodiesel at 115 PS at 4,800 rpm and 210 Nm at 2,400 rpm for cars built 09/1983-08/1987. US-trim output is not established. |
| Engine oil capacity | BMW's fill-quantity data lists 5.25 liters (about 5.5 US quarts) for the US 524td built 04/1983-08/1983 and 5.75 liters (about 6.1 US quarts) for later builds. |
| Reliability profile | Not established yet. We are still researching this engine. |
Where you find it
| US model | Built |
|---|---|
| E28 524td | 04/1983-12/1985 |
Technical Specifications
| Specification | Detail |
|---|---|
| Configuration | SOHC straight-six diesel, two valves per cylinder |
| Block | Cast iron |
| Camshaft drive | Belt |
| Displacement | 2,443 cc, 80 mm bore, 81 mm stroke |
| Compression ratio | 22.0:1 |
| Turbocharger | Garrett T03, without an intercooler |
| Injection | Swirl chamber injection with a distributor fuel injection pump |
| Output | 115 PS at 4,800 rpm and 210 Nm at 2,400 rpm (turbodiesel, 09/1983-08/1987) |
| Engine oil | 5.25 or 5.75 liters per BMW's fill-quantity data, plus 0.75 liter for the oil cooler after a repair. BMW of North America's oil chart (SI B11 01 15, February 2017) lists 5W-30 LL04 for all BMW diesel engines of model year 2011 and older; it does not name the M21 by code. |
| Coolant, firing order, engine management | Not established yet. |
Factory Deep Dive
A diesel built on the M20
Wikipedia says the M21 is based on the M20 petrol engine and has a cast iron block and a belt-driven camshaft like it. It lists reinforced connecting rods, cylinder heads, pistons and valves, and a reinforced crankshaft with seven bearings, compared with the M20.
Starting and turbocharging
Wikipedia describes a glow plug system BMW called instant start, and a Garrett turbocharger with no intercooler.
Naturally aspirated and later versions
Wikipedia says a naturally aspirated M21 arrived in 1985 and that electronically controlled injection pumps came from 1987. Neither is in BMW's US parts data for the 524td.
Service Parts at a Glance
These numbers come from BMW's US parts data (December 2019). Dates are BMW build dates. Check the exact car before ordering.
| Part | BMW part number | Note |
|---|---|---|
| Thermostat | 11531265085 | Fits the E28 524td (04/1983-12/1985) and also the M20 325e and 528e. BMW's data links it to 11531264668, also current. |
| Exchange water pump | 11519070765 | Fits the E28 524td (04/1983-12/1985). BMW's data links it to 11519070764, also current. |
| Fuel filter | 13322241303 | Fits the E28 524td (04/1983-12/1985). |
| Air filter element | 13721285521 | Fits the E28 524td (04/1983-12/1984). |
| Oil filter head | 11421285909 | Fits the E28 524td (04/1983-12/1985). BMW's catalog name for this part is oil filter head. |
Known Failure Points and Service Items
Not established yet. We found no BMW service bulletin, recall or training document for the M21. NHTSA's recall lookup returned no records for the BMW 524td in model years 1983, 1984, 1985 and 1986. That is a sample check, not a complete search.
Reliability Verdict
Not established yet. We are still researching this engine.
Power Potential
Not established yet. We are still researching this engine.
Cost of Ownership
Not established yet. We are still researching this engine.
Common Questions
Which US-market BMW had the M21 diesel?
BMW's US parts data lists the M21 only in the E28 524td, built 04/1983-12/1985.
Is the M21 a diesel or a gasoline engine?
The M21 is a 2.4 liter turbocharged straight-six diesel, according to Wikipedia.
How much oil does the M21 in the 524td take?
BMW's fill-quantity data lists 5.25 liters (about 5.5 US quarts) for the US 524td built 04/1983-08/1983 and 5.75 liters (about 6.1 US quarts) for later builds.
Does the M21 have a timing belt or a timing chain?
Wikipedia says the M21 camshaft is driven by a belt.
Did any non-BMW vehicle use the M21?
Wikipedia lists the Lincoln Continental and the Continental Mark VII (1984-1985) among M21 applications.
What replaced the M21?
Wikipedia says the M51 succeeded the M21.
Sources
- Wikipedia, BMW M21
- NHTSA recall lookup, BMW 524td
- BMW parts catalog and fill-quantity data, data date December 2019 (internal reference, not linked)
- BMW of North America SI B11 01 15, Engine Oil Quick Reference Chart, February 2017 (NHTSA copy)
