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Apr 29, 2023

10 Inline

Straight-six engines are only growing in popularity, so we thought we’d browse

Straight-six engines are only growing in popularity, so we thought we’d browse over the most significant and reliable examples throughout history.

Inline-six engines have always been an essential part of the automotive world, often finding themselves beneath the hood of some of the most reliable cars ever made. But with the introduction of specific emissions regulations and the growing popularity of downsizing as a result, even the world's most exotic cars are adopting six-cylinder engines now. Not that this is a bad thing: six-cylinders have proven to be one of, if not the most utile powertrain layout around, and manage to be small enough to keep the vast majority of the world's eco-warriors happy.

But let's not put a dampener on the story, and instead, we thought we’d celebrate the world's best straight six-cylinder engines by putting together a list of 10 of the most reliable examples ever made. You're unlikely find any of the world's least reliable car brands here, since the criteria specifically revolves around which engines last longest. So, if you're looking for the most reliable engine, please proceed.

Note: By using websites such as J.D. Power and Consumer Reports, we’ve been able to determine what some of the most reliable inline-six engines ever made are.

Straight off the bat, we begin with a strong contender for not just one of the most reliable inline-six cylinders built, but also one of the outright greatest engines ever made: Toyota's 2JZ-GTE block. Most famously associated with the 1993-1998 Toyota Supra A80, the 2JZ is known for its ridiculous tunability, with some keen enthusiasts capable of coaxing more than 1,000 hp out of them with minimal fuss. However, the downside to doing something like this is that the 2JZ does lose some of the reliability sparkle that has allowed it to remain so relevant for all these years.

Known for later evolving into the M52, the BMW M50 has been credited with being one of Munich's greatest pieces of engineering. It featured aluminum cylinder heads which lowered weight and increased heat dissipation efficiency, in addition to a fantastic fuel injection system that provided precise fuel delivery and, in turn, lead to an incredibly smooth drive. These days, BMW has a stellar reputation for manufacturing clever, reliable engines, and the straight-six M50 is undoubtedly one of the reasons for that. One of its most famous applications was in the 1998-1995 BMW 5 Series E34.

Related link: 10 European Car Engines That Don't Get Enough Recognition

The Noughties was a fantastic period for Mercedes-Benz, and was the decade that truly helped stamp its authority as one of the world's most trustworthy luxury carmakers. The vehicles it produced at the time can now be had for next to nothing, but still remain wonderful pieces of engineering – the Mercedes-Benz S320 (W220) is a prime example of that. It would make a strong case for making our list of the 10 best Mercedes-Benz ever for performance and comfort, thanks hugely to the wonderful 3.2-liter iteration of the Silver Arrow's OM648 block. Using common rail direct injection, aluminum construction, and an overhead camshaft design, the OM648 is one sturdy diesel block that will get you home on every single occasion

Alas, we arrive at the second coming of Godzilla, and the car that will forever be associated with one of the most loved gearheads of all time: Paul Walker. We’re referring to the Nissan Skyline R34 GT-R, of course, and the titanic RB26DETT motor it houses. It was initially deployed on the R32, and even found its way into racing – surely a road engine that is capable of competing in motorsport has got to be uber-reliable, right? Correct. Using a pair of turbochargers and sporting a host of strong internals, including a forged steel crankshaft, connecting rods and pistons, the RB26DETT is a true engineering marvel. We’d strongly recommend browsing over ‘2JZ vs RB26: how the two inline six-cylinder engines compare’ to see how the R34's engine stacks up against its eternal rival in the A80 Supra.

Not only is the Chevrolet 292 six-cylinder block the engine with the longest production life of all the examples on this list, but it very well stakes a claim for being the most reliable outright. It has grown to be loved by enthusiasts for the sheer number of aftermarket support on offer, while common folk appreciate the wide variety of cars that utilized the Chevrolet 292. The high torque output made it a thorough workhouse, and that also means it's still remains a hugely popular choice for anyone that wants reliability on a budget.

Related link: 10 Best Classic American Cars With V8 Engines

Of course a straight-six that was utilized by Jeep was always going to make an appearance here, and the famous 4.2L is the perfect entrant for the brand. Originally made by AMC, it was eventually deployed by Jeep in a number of its vehicles across a nearly 20-year span. Its cast iron construction and simple nature made it an instant hit, and continues to be a go-to option for so many people that want an engine that will run for moon miles and beyond. We’d love to see it beneath the hood of this modified 1981 AMC Jeep CJ-8 Scrambler!

The perfect entrant for the Swedish carmaker is its SI6 block that ran for over 10 years. It was created using an all-aluminum construction method and was often supported by a single turbocharger to deliver a softer power delivery. The underlying fact, though, is that the SI6 is impeccably reliable, and really marked Volvo's entrance into the industry as a genuine leader. It was also applied across a plethora of respectable models and essentially allowed Volvo to develop the steadfast reputation it now has. We’d love to see what would happen if this block is paired with the legendary Volvo P1800 Cyan.

Most remember the Ford Barra engine as a mighty block that led Ford's Australian version of the Falcon to huge success, but the foundations were actually laid back by the 1960-63 six-cylinder Ford Falcons. Using a revolutionary form of cast iron construction, in conjunction with an overhead valve design, and a ’Stovebolt Six’ fastening system, the original Barra engine was revered for its reliability and high torque output. It was capable of huge workloads at a time and really paved the way for so many great Ford models after it.

Perhaps the BMW M54 engine strikes the right chord between thrilling and affordable at present, in the form of a used BMW E46 M3. By employing a variable camshaft timing system and fuel injection, alongside a touch of the brand's Valvetronic technology, BMW had accidentally ended up manufacturing a block that was both powerful (unsurprisingly) and durable. Not only is the delivery smooth and the power residual, but it just loves to scream its way up the rev range. When you’re talking about reliable, no compromise engines, the M54 has simply got to be a part of the conversation.

Related link: 10 Iconic Cars That Revolutionized Automotive Engineering

Jaguar models of the 20th century are often associated with classy looks and supreme comfort, not to mention huge performances for that era. One thing they are very rarely known for is just how dependable they are as a direct result of the XK6 engine. There were a few hiccups with the E-Type, which also had the XK6 block, but the XK120, XK140, and XK150 models are nothing short of unbreakable. Triple carburetors, twin overhead camshafts, and a peak horsepower of 265 hp made this irresistible engine one of Jaguar's all-time greats – just check out Richard Hammond's restored Jaguar XK150 if you need any further explanation!

Shafiq is a petrolhead to his core, and has had a lifelong obsession with anything that came from Japan in the 90s. When he isn't driving, talking or writing about cars, he enjoys watching football and taking his German Shepherd on countryside adventures.His motoring journalism career so far has seen him write for publications like CarThrottle, DriveTribe, Electrifying and The Intercooler. Shafiq is also a double graduate, holding a bachelor's degree in journalism and a master's degree in automotive journalism.