Mercedes and the Renault 1.5 dCi K9K Engine

For weeks, rumours circulated that Mercedes might turn to BMW engines. The story has since been denied, but it brought to mind another - very real - connection between the Stuttgart brand and Renault.

Yes, Mercedes has already used a Renault engine - and it currently uses another one, although it now carries the HORSE badge, the French brand’s combustion-engine division in a joint venture with Geely. And it was no ordinary engine.

We are talking about the K9K, best known as the 1.5 dCi: one of the most widely produced Diesel units of the past 25 years, renowned for its efficiency, simplicity and longevity - although we will come to the big-end bearing shell issue. Its fuel consumption was so low that I believe I still hold the “unofficial record” for the most economical (and slowest…) lap of the Estoril Circuit:

A hero without a bearing shell…

The K9K arrived in 2001, at a time when Renault had established itself as a benchmark for compact Diesel engines. With a capacity of just 1,461 cm³, it featured four cylinders, common-rail direct injection and a variable-geometry turbocharger in the more powerful versions - from the 105 PS variants onwards (K9K 732 and later).

Over the years, it also gained an intercooler, a particulate filter and successive electronic management upgrades, while retaining the same DNA: low fuel consumption, smooth running and durability.

With a 76 mm bore and an 80.5 mm stroke, it represented a well-balanced mechanical design, capable of serving in thousands of different models and meeting several European emissions standards, from Euro 3 to Euro 6. A genuine example of longevity.

It is true that the first generation of the K9K 1.5 dCi had a poor reputation for many years. Premature big-end bearing shell wear, unreliable turbos and a temperamental injection system caused owners more than a few headaches.

As you will already have gathered from the video shared above, I was one of those owners. Yet perhaps because I used only high-quality oil (always!), I encountered problems solely with two injectors (at 170,000 kilometres).

At around 220,000 kilometres, as a precautionary measure, I decided to have the big-end bearing shells replaced. Fortunately, the work proved unnecessary: they showed no wear. I sold my Renault Mégane II with 300,000 kilometres on the clock and, by all accounts, it is still out there…

Later, I bought a 2005 Renault Scénic II and had zero engine problems. The K9K engine’s longevity clearly surpassed that of other Renault components, such as the electric window mechanisms, central locking and electric handbrake. But let us return to the “hero” of this Autopédia article…

The 1.5 dCi engine from 65 to 116 PS

Over almost 20 years, the 1.5 dCi steadily gained power and refinement. It began modestly with 65 PS and 160 Nm of torque, eventually reaching 116 PS and 260 Nm in its final versions, all while retaining very low fuel consumption and above-average reliability - provided maintenance was carried out properly and on schedule.

As mentioned earlier, this engine’s lifespan was so extensive that it went through four generations over 20 years. As I explained a moment ago, the most troublesome was the first (2001–2005).

The second generation (2005 to 2010) brought improvements in both power and reliability, although its main highlight was the introduction of a six-speed manual gearbox. Fuel consumption benefited, as did compliance with increasingly restrictive emissions standards.

Some argue that the third generation (2010–2016) was the best in reliability terms. The weaknesses of the past had been resolved, while the K9K had not yet needed to contend with emissions rules as severe as those affecting the fourth generation (2016–2021).

During this period, Renault’s 1.5 dCi engine powered models including the Clio, Mégane, Scénic, Kangoo, Modus, Dacia Sandero, Logan and Dokker, as well as the Micra, Juke, Note and Qashqai through the Renault-Nissan Alliance. And, surprisingly to some, it also found its way into the Mercedes-Benz A-Class, B-Class and Citan.

A French engine, proudly German

For Mercedes, the K9K engine was a pragmatic answer. The aim was to offer entry-level versions with low fuel consumption and reduced running costs, ideal for fleets and markets where Diesel still dominated. Portugal was one such market for many years.

The decision was not merely strategic; it was technical as well: the 1.5 dCi was compact, lightweight and ideally suited to the transverse architecture of the German brand’s smaller models. The result was an unlikely yet effective partnership between excellent German brand image and French engineering.

Returning to Portugal, it was the perfect match for the national car market for many years. Renault and Mercedes spent a long time occupying first and second place in the sales charts, both driven above all by the humble but hard-working K9K.

Although it remained 100% French, this engine received several upgrades for Mercedes duty, primarily to make it smoother. In 2018, we wrote about those differences:

An icon disguised as a workaday engine

Today, the K9K is regarded with respect - and a degree of nostalgia - by enthusiasts and mechanics alike. It survived more than two decades of emissions regulations, millions of kilometres and an enormous range of different models.

In a world preparing to move away from Diesel, the 1.5 dCi will go down in history as one of the last truly universal engines. An engine born at Renault, passed on to Nissan and Dacia… and which, for a time, made the three-pointed star shine with a French accent.

And yes, I also prefer petrol engines, but some Diesel engines deserve more than a footnote. The K9K is one of them, as is the PD130, but that is a story for another day…