Mercedes and Renault: the K9K 1.5 dCi story

For weeks, rumours swirled that Mercedes might end up turning to BMW engines. The story was later debunked, but it did revive memories of another link - a genuine one - between the Stuttgart brand and Renault.

Yes, Mercedes has used a Renault engine. And although it now uses a different unit carrying the Horse badge - the French brand’s combustion-engine division in a joint venture with Geely - that earlier collaboration involved no ordinary engine.

It was the K9K, better known as the 1.5 dCi: one of the most widely produced Diesel engines of the past 25 years, celebrated for its efficiency, simplicity and durability - we will get to the con-rod bearing shells in a moment. Fuel consumption was so low that I still think I hold the “unofficial record” for the most economical (and slowest…) lap of the Estoril Circuit:

A hero without a cape (or con-rod bearings…)

The K9K arrived in 2001, at a time when Renault was establishing itself as a benchmark for compact Diesel engines. With just 1,461 cm³ of displacement, it featured four cylinders, common-rail direct injection, and a variable-geometry turbocharger on the more “punchy” versions - from the 105 cv variants (K9K 732 onwards).

As the years went by, it also gained an intercooler, a particulate filter, and successive upgrades to the electronic management, while always keeping the same DNA: low consumption, smooth running and toughness.

With a 76 mm bore and an 80.5 mm stroke, it was a fine example of mechanical balance, able to serve in thousands of different models and meet multiple European emissions standards, from Euro 3 through to Euro 6. A real lesson in longevity.

That said, the first generation of the K9K 1.5 dCi carried a poor reputation for many years. Premature wear of the con-rod bearing shells, unreliable turbos and a temperamental injection system caused plenty of headaches for owners.

As you may have gathered from the video shared above, I was one of those owners. Still, perhaps because I used only high-quality oil (always!), my only issues were with two injectors (at 170,000 km).

At around 220,000 km, as a precaution and purely as preventative maintenance, I asked for the con-rod bearing shells to be replaced. Thankfully, it turned out to be unnecessary: there was no wear to report. I sold my Renault Mégane II with 300,000 km and, by all accounts, it is still out there…

Later on, I bought a Renault Scénic II (2005) and had zero engine problems. Clearly, the K9K block’s lifespan outlasted other Renault components, such as window regulators, central locking or the electric parking brake. But let’s return to the “hero” of this Autopédia article…

1.5 dCi engine from 65 to 116 cv

Over almost 20 years, the 1.5 dCi gradually gained power and refinement. It started out modestly with 65 cv and 160 Nm of torque, and ended up at 116 cv and 260 Nm in the final versions, all while keeping fuel consumption extremely low and delivering above-average reliability - provided maintenance was carried out properly and on time.

As mentioned earlier, this engine’s working life was so long that, over two decades, it went through four generations. The most troublesome - as I explained a moment ago - was the first (2001–2005).

In the second generation (2005 to 2010), it saw improvements in both output and reliability, but the major highlight was the adoption of a six-speed manual gearbox. Consumption benefited, and so did compliance with tighter emissions rules.

Many argue that the third generation (2010–2016) is the best for reliability. The weak points of earlier years were sorted, and the K9K still did not have to contend with emissions requirements as severe as those faced by the fourth generation (2016–2021).

During this time, Renault’s 1.5 dCi powered models such as the Clio, Mégane, Scénic, Kangoo and Modus, plus the Dacia Sandero, Logan and Dokker, and also the Micra, Juke, Note and Qashqai through the Renault–Nissan alliance. And, perhaps 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, choosing the K9K was a pragmatic decision. The aim was to offer entry-level versions with low consumption and reduced running costs, well suited to fleets and to markets where diesel continued to dominate. Portugal was one of those markets for many years.

The decision was not only strategic; it was technical too. The 1.5 dCi was compact, light, and fitted neatly into the transverse architecture of the German brand’s smaller models. The outcome was an unlikely but effective pairing of German brand prestige with French engineering.

Back in Portugal, this combination worked perfectly for a long time in the national car market. Renault and Mercedes held first and second place in the sales charts for years, driven above all by the humble yet hard-working K9K.

Although it remained a 100% French engine, Mercedes introduced a number of tweaks for its applications, mainly to make it run more smoothly. In 2018, we wrote about those differences:

An icon disguised as a utility engine

Today, the K9K is viewed with respect - and a certain nostalgia - among enthusiasts and mechanics. It endured more than 20 years of emissions standards, millions of kilometres, and an endless range of different models.

In a world preparing to move away from Diesel, the 1.5 dCi will be remembered as one of the last truly universal engines. An engine born at Renault, that went through Nissan and Dacia… and that, for a time, made the three-pointed star shine with a French accent.

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

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