Mercedes W124 Diesel: The Most Durable Chapter of the Series

When you talk about the Mercedes W124, at some point you talk about diesel. Not because the petrol engines are uninteresting – but because the diesel engines of this series tell their own story. A story of common sense that still has character. Of durability that today sounds like a legend. And of engines that were built when Mercedes still built as if every vehicle had to last forever.

The diesel variants of the W124 are still the best-selling representatives of the series – and have long since become sought-after classics themselves.

The Engine Families: OM601, OM602, OM603

Before understanding the individual models, one must know the engines. Mercedes used three diesel aggregates in the W124, all stemming from the same engineering philosophy: pre-chamber diesel technology, cast iron engine blocks, chain instead of belt drive. Robust, easy to maintain, designed for eternity.

OM601 – Four-cylinder, 2.0 litres The smallest of the three. Four cylinders, pre-chamber injection, solid down to the last screw. Not a sports engine, but one that spells out the word "durability" like no other.

OM602 – Five-cylinder, 2.5 litres The exotic of the family. Five cylinders are rare in diesel engines – in the W124, they are a distinguishing feature. The OM602 runs smoother than the four-cylinder and more powerfully than its displacement number would suggest. It also existed as a turbo variant.

OM603 – Inline six-cylinder, 3.0 litres Six cylinders, silky smooth running, the top model of the diesel range. The OM603 is the engine about which taxi drivers tell legends: 600,000 kilometres, first gearbox still original. With a turbocharger, it became the most powerful series production diesel from Mercedes to date.

The Models in Detail

200D – the Sensible One

Engine: OM601 · 2.0 litres · 4-cylinder · 72 hp
Year of manufacture: 1984–1993

The 200D is the most frequently built diesel model of the W124 and the car you saw everywhere – and can barely find today. Because what was once considered a pure utility vehicle has now become a rare contemporary witness.

72 hp sounds like little – and it is. The 200D never claimed to be sporty. It drives. It runs. It stops. On the highway, it reaches almost 160 km/h, which is already a feat for it. But it does so with a reliability that modern vehicles can only dream of.

What makes it a classic is precisely this down-to-earthness: no turbo, no complexity, no weakness. Whoever finds a well-preserved 200D finds a vehicle that could still drive for 30 years.

250D – the Five-cylinder Insider Tip

Engine: OM602 · 2.5 litres · 5-cylinder · 90 hp
Year of manufacture: 1985–1993

The 250D is the model that connoisseurs choose. The five-cylinder diesel engine is a rarity in this class – and it makes its presence felt. Anyone who sits in a 250D cockpit and starts the engine hears the unmistakable clatter of a five-cylinder: slightly asynchronous, slightly rough, completely distinctive.

With 90 hp, it is significantly more confident in everyday use than the 200D. Long distances on the motorway are relaxed, and fuel consumption remains in reasonable ranges. Mechanically, the OM602 is considered almost as indestructible as its siblings – well-maintained examples easily run over the 400,000-kilometre mark.

Today, the 250D is slightly in the shadow of the larger six-cylinders, which often makes it cheaper on the market – unjustly.

300D – the Six-cylinder Classic

Engine: OM603 · 3.0 litres · 6-cylinder · 109 hp
Year of manufacture: 1985–1993

The 300D is the diesel that Mercedes enthusiasts seek. Six cylinders that run so smoothly that you almost forget it's a diesel. The OM603 is quiet, cultured – a diesel with manners.

109 hp is perfectly sufficient for the vehicle class and weight. The 300D glides rather than propels. It's not a car for the impatient – but one for people who know that the journey itself is the destination.

As an estate (S124/300 TD), the 300D has become an absolute institution. The estate body, the inline six-cylinder, the W124 chassis – a combination that still doesn't drive onto any campsite without attracting attention.

300D Turbo – the most powerful diesel of the series

Engine: OM603 with exhaust gas turbocharger · 3.0 litres · 6-cylinder · 143 hp
Year of manufacture: 1987–1993 (Saloon), later also as Estate model

The 300D Turbo is what happens when an already excellent engine gets a supercharger. 143 hp from a production diesel of this era – that was a statement when it was introduced in 1987. Mercedes not only had the most powerful production diesel vehicle in its own lineup, but one of the most powerful worldwide.

The turbo makes the OM603 noticeably more powerful in the mid-range. The initial weakness typical of turbodiesels at the time is present – those who wait for the supercharger to kick in will be rewarded. On the highway, the 300D Turbo moves with a confidence that clearly leaves the naturally aspirated version behind.

Mechanically, the turbo variant requires a bit more maintenance than the naturally aspirated one – turbocharger, intercooler, and injection system demand regular attention. Those who provide this will have one of the most coveted W124s of all.

After the Facelift: the E-Class Diesel (1993–1995)

From 1993 onwards, the W124 officially carried the designation "E-Class" in its name – and the diesel model designations switched to the scheme known today. The 250D became the E 250 Diesel, the 300D became the E 300 Diesel, and the 300D Turbo became the E 300 Turbodiesel.

Technically, little changed in the engines themselves under the facelift models – the series was already mature in its final years of production. Externally, the facelift brought revised bumpers, new exterior mirrors, and a refreshed interior. Collectors appreciate both generations; the pre-facelift is considered visually clearer, the facelift a bit more comfortable inside.

What all W124 Diesels have in common

Pre-chamber injection instead of direct injection

All W124 diesel engines use pre-chamber injection. This makes them slightly less efficient than modern direct injectors – but significantly more robust and quieter. No common rail, no high-pressure pump that gives up after 200,000 kilometres.

No timing belt

All OM601, OM602, and OM603 engines are driven by a timing chain. No timing belt change intervals, no sudden engine damage due to a broken belt. The chain runs – probably forever, if the oil is right.

Glow plugs instead of spark plugs

The only thing required for a cold start: pre-glowing. In well-maintained examples, this only takes a few seconds. After that, the engine starts – reliably, even after long periods of inactivity.

Mechanical injection pump

The Bosch injection pumps of these engines are precision devices from a time when injection systems still had to function without electronics. They are maintainable, repairable, and designed for life with good care.

What to look for when buying?

Check oil change intervals: This is the most important question for any OM diesel. Engines of this series do not tolerate neglected oil changes. Those who changed it regularly can hope for 500,000 km and more. Those who didn't – buy problems.

Soot clouds during warm start: A warm engine that produces smoke when starting can be a sign of worn injectors or turbo bearing damage (in the 300D Turbo).

Body before engine: W124 engines are robust. Bodies too – but rust on sills, wheel arches and under rubber seals is the most common problem in this series.

Automatic or manual transmission: Both transmissions are reliable. The automatic (W4A040) is considered almost indestructible if the transmission fluid has been changed regularly.

Conclusion: Diesel that lasts

The W124 diesel models are not vehicles for people seeking attention. They are vehicles for people who know what quality means – and are willing to drive slowly for it.

What these engines achieve is no coincidence. It is the result of an engineering culture that is now history itself. Anyone who finds a well-maintained 300D or a rare 250D today finds not just a car. They find a statement – built in steel, cast iron, and the conviction that a vehicle must last.

Save the Classics – for people who not only drive their classic, but understand it.

You can find our W124 and S124 products here: 124 Collection