BMW M41 and M51 Diesel Engines

BMW M51 diesel engine

M51 in an E36 325tds.


BMW had sold M21 diesels in the E30 324td and E28 524td for many years but only in some markets and never in the UK or USA where demand was judged to be poor. But the newer generation of turbo diesels being sold by their rivals meant that BMW had to respond with a new range of smoother engines which set a higher benchmark. These new engines powered the E36 three series, E34/E39 five, Range Rover and Opel Omega.

In late 1991 (later in the UK) the M51 emerged to rave reviews. The engine set new standards in the market place for executive cars. Unlike the M21 all M51s had a turbo, however the intercooler was optional and only fitted to "tds" models which benefited by around 25 bhp.

Several years after the introduction of the M51 in 1994 a four cylinder M41 was released. This was basically two thirds of an M51 and displaced 1700cc. It sold particularly well in the UK as a Compact. The E38 725tds was never sold in the UK and that was probably no bad thing, it needed a three litre really.


The M51 had the same swirl chamber and cylinder spacing as the M21. But whereas with the M21 the goal had been low cost and commonisation of parts with the M20 the M51 had fewer cost constraints and far more dedicated components. BMW pushed the boat out a bit further this time. Like the M50 petrol counterpart the valves were hydraulic and the engine was chain driven. Unlike the M50 this was a 12 valve engine, this was acceptable for a lower revving diesel especially one with forced induction.

The engine was designed from the outset to work with a catalytic converter used exhaust gas recirculation (EGR) to further lower emissions. Just like the M50 the M51 used a serpentine belt arrangement to power ancillaries.

The 2.5tds cars benefited from an intercooler to reduce the temperature of the intake charge and this greatly benefited power. All M41s had the intercooler.

For the 1996 launch of the E39 an M51TU update was released. This had the same peak power but slightly more torque.

Using similar technology to the M43TU the M41 had a plastic intake manifold, so did the M51TU which is a handy recognition feature. It produced 90bhp thanks to a standard intercooler and saw service in the E36 318tds.

BMW M41 diesel engine

M41 in an E36 318tds.


Code Size Power
Manufactured Bore x
Timing Weight
VANOS Used in
M41 1.7 90 @ 4400 140 @ 2000 53 82.4 1995 - 2000 80x82.8 Chain 108 No E36 318tds
M51 2.5td


115 @ 4800

143 @ 4800

162 @ 1900

190 @ 2200





1991 - 1996 80x82.8 Chain 132 No E36 325TD/S, E34, E39
M51TU 2.5td


115 @ 4800

143 @ 4600

170 @ 1900

210 @ 2200





1996 - 2001 80x82.8 Chain 132 No E39, later E36s


BMW M51tu diesel engine

M51TU in an E39 525tds.


The enemy of all diesel engines is carbon deposits. The EGR valve which recirculates dirt through the engine to reduce emissions makes this worse. The first step for any poorly running diesel is to strip down the entire intake tract and clean it, especially the EGR valve. Many folk blank off the EGR valve but this may not be legal where you live.

This generation of diesels take longer to warm up than a petrol engine because there's no throttle plate so the cylinder gets a big gulp of cooling air at idle. For this reason you really want to avoid cars that have been used only for lots of short journeys. They will seldom have reached normal operating temperature and will be filthy inside.

The other worry is the turbo, the only thing you can do to prolong it's life is to use good oil and change it at the correct intervals. Never let the level run low and let the car cool down gradually after very hard driving. A kit is available cheaply to replace the bearing and seals.

These engines are often chipped by their owners. Generally this isn't a bad thing and can have excellent results. But beware of used cars where things have been taken a bit too far.

Always check the engine earthing strap if there's a problem.

If it won't start when hot or takes ten seconds to catch it may be because the ECU isn't turning the glow plugs on. Third party fixes are available.

If you drive this like a high performance engine it will drink fuel accordingly. For good economy it's best to be gentle and use the cruise control a lot.

On the bright side you don't have the swirl flaps or particle filter problems of the later diesels to worry about.

These are durable units if kept clean internally. But economy and power can be truly dreadful on a badly maintained one. A good dose of Redex before an oil change never hurts, nor does a Winns engine oil flush.