Why Some Mercedes V6 Engines Use 12 Spark Plugs

For the most part, engines have one spark plug per cylinder to ignite fuel and keep the combustion process running as it should. A V6, for instance, would have six spark plugs. However, as with nearly every aspect of the automotive industry, it's not a hard-and-fast rule. 

Some engines from Mercedes-Benz, for example, use two spark plugs per cylinder. One such engine is the M112 V6. Why does it use 12 spark plugs? According to Mercedes, it was all about emissions and efficiency. The two spark plug design worked in tandem with a three-valve layout to provide a cleaner, more efficient burn of fuel. The second plug fit because each cylinder had only one exhaust valve. 

The 2.8-liter M112 first saw use in the Mercedes E-Class in March 1997 and joined the C-Class that June. Mercedes' M113 V8, including the version in the performance-oriented C 43 AMG from the same era, used the same dual spark plug technology. The German manufacturer claimed that the twin-plug V6 and its other upgrades cut the 1997 C 280's fuel use by 9% over the inline-six it replaced.

Back in the late 1990s and early 2000s, Mercedes was as tech-forward as it has always been, but in a different direction than what we are used to seeing from the quintessential German automaker today, which is developing electric motors that can make its future EVs lighter. Mercedes-Benz's own historical archive emphasizes value as one of the foremost qualities going into the M112 and the C-Class.

While a Mercedes was never a less expensive option than something like a Ford or Toyota, the brand wanted to give you more "bang for your buck" (literally in the case of better ignition) with a C-Class or E-Class compared to, say, a BMW 3 Series or 5 Series. The base model C-Class from the era, for instance, had side-impact airbags as standard.

That overall design and marketing philosophy translated over to the brand's engineers, who devised clever tricks like dual spark plugs to boost fuel economy. Mercedes was doing this long before the most effective fuel efficiency technologies, like mild hybrids, auto stop-start, or cylinder deactivation, became commonplace.

You might spend more when it's time to change spark plugs, but you'll make up for it by using less fuel. Two spark plugs per cylinder might not seem like something that's all that exciting, at least compared to a high-strung AMG, but for a Mercedes buyer, efficiency makes a lot of difference.