The Most Power-Dense Diesel Engine Available In 2024 (2025)

What we know now as the Mercedes-Benz GLS SUV has existed in the Mercedes-Benz stable for almost two decades, and in that time, has seen several iterations rise and fall. The founding member of the luxury SUV offering debuted in 2006 under the GL-Class branding. The second-generation model debuted in 2013, following the production run of the first-gen model that spanned from 2006 to 2012. It would be in 2016 that the world saw the first appearance of the "GLS" nomenclature that was applied to the facelifted variation for the second-generation GL-Class SUV.

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The third-generation GLS range debuted in 2019 and featured six derivatives, of which two models, the GLS 350d and 400d, were the lineup's diesel offerings. After a model update in 2023, the current lineup consists of six derivatives of the GLS nameplate, two of which are powered by diesel engines, the GLS 350d and GLS 450d. The GLS 450d, which has replaced the GLS 400d, is one of the few diesel options to exist in the 2024 model year range and happens to be powered by the most power-dense diesel engine available in 2024. Unfortunately, it's not available in the USA, as the list of diesel cars still sold here is shrinking rapidly.

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Mercedes GL/GLS Diesel Engine Evolution

First generation GL-Class

The Most Power-Dense Diesel Engine Available In 2024 (3)

In the first-generation GL-Class range, the number of diesel engine configurations drastically outnumbered the petrol-powered models. The diesel-powered derivatives of the GLS were powered by either a 3.0-liter turbodiesel V6 or a 4.0-liter twin-turbo V8. The 3.0-liter turbocharged V6 powered the GL320 CDI from 2006 until 2009. In this form, the V6 engine commanded 221 hp (74 hp/liter) and 376 lb-ft of torque until the facelifted version debuted in 2009, whereby the GL320 CDI adopted the GL350 CDI name and its 3.0-liter V6's output dropped to 181 hp (60 hp/liter) and 236 lb-ft. In that same year, Mercedes introduced the GL350 BlueTEC, which featured urea injection in its exhaust system to comply with the 50-state emissions regulations. Urea is a colorless and odorless substance that is used in diesel engines to reduce nitrogen oxide emissions by converting the chemical into water vapor and carbon dioxide during the exhaust treatment process.

This model utilized a more power-dense iteration of the turbocharged 3.0-liter V6, which produced 208 hp (69 hp/liter)and 398 lb-ft. In 2010, the power of the GL350 CDI would increase to 261 hp (87 hp/liter) and 457 lb-ft, which would remain unchanged until the introduction of the next-generation model. The GL420 CDI was the model that debuted alongside the GL320 CDI but was motivated by a much larger and powerful 4.0-liter twin-turbo V8 that produced 302 hp (76 hp/liter) and 516 lb-ft. Similarly to the GL320 CDI, the V8 counterpart was rebadged in 2009 and called the GL450 CDI, but was decommissioned a year later.

Second Generation GL/GLS-Class

The Most Power-Dense Diesel Engine Available In 2024 (4)

The second-generation GL-class, the X166 generation, debuted in 2012 and was in production until 2019. It would be this generation that the first rendition of the "GLS" nameplate would appear. The GL-Class featured a single diesel derivative, the GL350 BlueTec, from 2012 up until the introduction of the updated second-gen SUV. Following the adoption of the GLS nomenclature, the 350d 4MATIC retained the 3.0-liter turbodiesel V6 that the pre-facelift model employed, and produced 255 hp (85 hp/liter) and 457 lb-ft.

Third Generation GLS

The Most Power-Dense Diesel Engine Available In 2024 (5)

The third-generation GLS debuted in 2019 and is still in production at the time of the publication of this article. This generation, referred to as the X167 generation, would feature just two diesel derivatives at the time of its inception, the GLS 350d and the GLS 400d. A key aspect of the new generation's powertrain was the inclusion of the firm's hybrid technology that was not only equipped in the petrol derivatives but its diesel counterparts too. In 2023, Mercedes unveiled the updated version of the X167 generation GLS that resulted in the assimilation of the 400d model into the 450d model, which is positioned as the more powerful diesel option in the current lineup.

Dissecting The Diesel Heart Of The GLS

The Most Power-Dense Diesel Engine Available In 2024 (6)

At the core of the Mercedes-Benz GLS 450d is a turbocharged 3.0-liter in-line six-cylinder diesel engine, internally known as the OM656 engine. This diesel engine has been in production since 2017 but first appeared in the GLS in 2019 after the debut of the third-generation model. In 2019, pre-facelift, the six-cylinder offered power to the GLS 350d and GLS 400d models. The OM656 engine consists of an aluminum engine block and cylinder head. Other characteristics of this engine include a common rail fuel system, a BorgWarner turbocharger, and a chain-driven timing drive system. Compression ratios have changed considerably compared to the initial rendition of the GL/GLS lineage. Compared to the 3.0-liter turbodiesel V6 that was equipped in the first generation GL-Class model, which featured a compression ratio of 18.0:1, the current diesel power plant operates at a much lower compression ratio of 15.5:1.

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Peak power output for the 450d is rated for 367 hp at 4,000 rpm, meaning that this model's diesel engine produces 122 hp/liter. Additionally, the engine is rated for a peak torque of 553 lb-ft of torque from 1,350 rpm to 2,800 rpm. A key feature of the third-generation GLS engine configuration is the 48-volt mild hybrid technology, previously referred to as the EG Boost system. Mercedes' 48-volt mild hybrid system is centered around the Integrated Starter Generator which connects the 9-speed automatic transmission of the GLS 450d to its driveshaft. The ISG is designed to replace the conventional starter and alternator. The benefits of the 48-volt mild hybrid system are that it can offer the engine a boost of power when needed, and in the case of the 450d, the system outputs a boost of 20 hp and 148 lb-ft of torque. Additionally, the system also affords the engine reduced fuel consumption.

Size Matters

Model

Mercedes GLS 450d 4MATIC

Ford F-250 Super Duty

Chevy Tahoe

GMC Sierra 1500

Engine

3.0-liter, turbocharged, inline six-cylinder

6.7-liter, turbocharged, V8

3.0-liter, turbocharged, inline six-cylinder

3.0-liter, turbocharged, inline six-cylinder

Horsepower

367 hp @ 4,000 rpm

500 hp @ 2,600 rpm

277 hp @ 3,750 rpm

305 hp

Torque

553 lb-ft @ 1,350 rpm - 2,800 rpm

1,200 rpm @ 1,600 rpm

460 lb-ft @ 1,500 rpm

430 lb-ft

Hp/liter

122 hp/liter

75 hp/liter

92 hp/liter

102 hp/liter

The importance of an engine's power density is that it provides a look into how efficient an engine is at creating energy, in correlation to the amount of displacement. A higher power density allows for the use of smaller engine sizes or form factors. An example of this in the GLS lineage is the move from the 76-degree V6 to a more compact inline six-cylinder engine configuration as the power density of the latter engine was better than the second-generation's engine. Compared to the range of diesel-powered trucks and SUVs available in 2024, none have a higher power density than the updated GLS 450d. However, Mercedes has another diesel engine that powers an entirely different vehicle class.

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In Mercedes' ranks is its distinguished Sprinter cargo van. Among the various body-style configurations and trim levels, is the firm's omnipresent High Output 2.0-liter four-cylinder diesel engine. Interestingly, compared to the much larger diesel engines in the table above, the Sprinter van's four-pot is much more power-dense. Peak power is rated at 208 hp @ 3,800 rpm and 332 lb-ft @ 1,400 to 2,400 rpm. As a result of less displacement and the peak horsepower, this diesel four-cylinder produces 104 hp/liter. That beats all the large trucks we mentioned earlier.

Diesel-powered vehicles are a slowly dwindling subspecies. The increasing tightening of emissions regulations, alongside the cost imposed on manufacturers to continue producing diesel-powered passenger vehicles, will likely continue to cause the available number of diesel-powered vehicles to decrease.

The Most Power-Dense Diesel Engine Available In 2024 (2025)
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