Are Straight-Six Diesels Still Worth It in 2025?
If you’ve ever found yourself daydreaming about the golden era of premium diesels, you’re not alone. There was a time when a lusty, turbocharged straight-six diesel was the go-to choice for anyone who wanted serious pace and long-legged efficiency. But fast-forward to 2025, and these engines are rapidly becoming unicorns—rare, desirable, and on the brink of extinction. So, is it still worth hunting one down? Let’s dive in.
Why Did Premium Diesels Become So Popular in the First Place?
It’s easy to forget just how dominant diesel engines once were in the premium car world. Back in the early 2000s, even Formula 1 prodigies like Jenson Button were caught pushing the limits in diesel-powered BMWs. The appeal was simple: torque-rich performance, impressive fuel economy, and a sense of effortless cruising that petrol engines struggled to match.
Diesel’s rise wasn’t just about road cars, either. Audi’s relentless success at Le Mans with their TDI engines cemented diesel’s reputation for durability and power. By the end of the decade, diesel was the default choice for many luxury buyers—whether you were after a compact executive saloon or a V12-powered flagship.
But then, the landscape shifted. Emissions scandals, tightening regulations, and the rapid advancement of hybrid and electric tech started to erode diesel’s dominance. Suddenly, what was once a no-brainer became a question mark.
What’s Left for Diesel Enthusiasts in 2025?
Today, finding a premium straight-six diesel feels a bit like searching for buried treasure. BMW, once a stalwart of the genre, is quietly phasing out diesel from its non-SUV lineup. Audi’s range has shrunk to a handful of four-cylinder TDIs and the occasional V6. Even the mighty Volkswagen Group, with all its engineering prowess, has dialed back its diesel ambitions.
But there are still a few gems left—each with its own unique flavor. For this deep dive, let’s focus on three standout contenders: the Alpina D4 S Gran Coupé, the Range Rover Sport D350, and the Mercedes-Benz E450d Estate. All three pack straight-six, twin-turbo diesel engines with mild hybrid assistance, all-wheel drive, and enough power to make you question whether diesel’s time is really up.
How Does the Alpina D4 S Stand Out from the Crowd?
Climbing into the Alpina D4 S feels like slipping into something rare and special. Alpina, soon to be fully absorbed into BMW, has always been about understated luxury and surprising performance. The D4 S is no exception.
Under the hood, you’ll find the B57 straight-six—an engine that’s been quietly evolving since 2015. Alpina’s tweaks give it a bit more punch than the now-defunct BMW M440d, and the result is a car that’s both quick (0-62mph in around five seconds) and genuinely opulent. The ride is plush, the interior is beautifully finished, and there’s a sense of occasion every time you drive it.
What really sets the Alpina apart is its balance. It doesn’t beg you to wring it out at every opportunity. Instead, it encourages a more relaxed, confident approach—one where you savor the torque and the effortless way it covers ground. The extended shift paddles are a tactile delight, and the low-end diesel rumble is deeply satisfying.
But there’s a catch: production ends in December 2025, and order books close by July. If you want one, you’ll need to move fast.
Is the Range Rover Sport D350 Still the King of Luxury SUVs?
Switching from the Alpina to the Range Rover Sport is a study in contrasts. The Sport is big—really big—and it wears its luxury credentials on its sleeve. The D350 model, with its Ingenium straight-six diesel, is the most potent diesel option in the lineup.
On paper, the Range Rover doesn’t quite match the Alpina for power-to-weight ratio, but in the real world, it’s more than quick enough. The engine feels robust, and the augmented soundtrack adds a bit of drama when you’re in the mood. Dynamic mode lets you play with the paddle shifters and even loosen the stability control—a rarity in today’s SUV market.
However, the Sport’s sheer size can be a double-edged sword. On narrow country roads, it feels every inch of its width, and the reliance on touchscreen controls for drive modes can be distracting. The days of big, glove-friendly buttons are gone, replaced by sleek digital interfaces.
Despite these quirks, the Range Rover’s ability to isolate you from the outside world is unmatched. The ride is supple, the steering is carefully tuned, and the cabin is a sanctuary. It’s no wonder that, according to recent JLR data, 44% of Range Rover Sport buyers still opt for diesel—compared to just 7% who choose pure petrol.
How Does the Mercedes-Benz E450d Estate Compare?
If the Alpina is about rarity and the Range Rover about presence, the Mercedes-Benz E450d Estate is all about quietly getting everything right. From the moment you settle into the driver’s seat, surrounded by a panoramic display and high-quality materials, it’s clear this is a car designed for those who appreciate the finer details.
The E450d’s OM656 straight-six diesel is a marvel of modern engineering. It delivers a mountain of torque from just over 1,000rpm, making the car feel brisk and responsive despite its size. The gearbox is silky-smooth, and the air suspension soaks up bumps with ease.
What’s impressive is how the E450d manages to blend performance, comfort, and practicality without any obvious compromises. It’s not trying to be a performance car, but it’s genuinely rewarding to drive—especially on challenging British roads. The four-wheel drive system is playful yet secure, and the cabin is a haven of tranquility, complete with subtle luxury touches like perfume-dispensing air vents and knurled metal controls.
Mercedes has been coy about the future of diesel in its lineup, but for now, the E450d stands as a testament to what a well-executed diesel can offer.
Are Straight-Six Diesels a Dying Breed—And Should You Care?
The numbers don’t lie: diesel’s share of the new car market has plummeted in recent years. According to the European Automobile Manufacturers Association, diesel accounted for just 16.4% of new car registrations in the EU in 2023, down from over 50% a decade earlier. Hybrid and electric vehicles are rapidly filling the gap, and stricter emissions standards are making it harder for diesels to compete.
But here’s the thing—if you value long-distance comfort, effortless torque, and real-world efficiency, a straight-six diesel still makes a compelling case. These engines are smooth, powerful, and surprisingly frugal. They’re also some of the last of their kind, which adds a certain allure for enthusiasts and collectors alike.
If you’re considering one, don’t wait too long. Production windows are closing, and the shift to electrification is only accelerating. For those who appreciate what these engines represent, now is the time to act.
The Takeaway: The Last Great Diesels Are Here—But Not for Long
If you’ve ever been tempted by the idea of a premium straight-six diesel, 2025 might be your last real chance to experience one new. The Alpina D4 S is a hidden gem, the Range Rover Sport D350 is a masterclass in luxury, and the Mercedes E450d Estate is quietly brilliant in every way that matters.
Will diesels ever reclaim their former glory? Probably not. But for those who know what makes these engines special, the current crop is a fitting swan song. Just remember—if you do decide to take the plunge, maybe keep your right foot in check on those French motorways.