The automotive world has had a long love affair with inline-six engines. A design popularized during pre-war aircraft, inline-six, or rather a straight-six engine design refers to a piston engine with six cylinders laid out in a straight line alongside the engine's crankshaft. This layout was the most popular design for six-cylinder engine classic cars until the V6 design came along during the mid-20th century.

RELATED: The Best Chevy Corvette Engines For Performance And Speed

Come the 2000s, many automakers ditched the traditional inline-six design for the narrower and compact V6 layout. Still, a few automakers, such as BMW and Mercedes-Benz, build modern inline-six engines today. While V6 engines produce incredible power, enthusiasts, and tuners favor the inline configuration for several reasons. Compared to V6 engines, inline-six engines have fewer moving parts, reducing the potential for wear and tear, thus boosting the engine's durability. The simple and balanced design also reduces engine vibrations and stress, contributing to increased reliability. On top of that, inline-six engines have superior low-end torque over their V6 counterparts.

Although V6 engines can be durable in their own right, inline-six engines deserve more respect for their sturdy nature. If you are in the market for a six-cylinder engine used car, below are 10 examples of inline-six engines that boast bulletproof reliability.

We took data from different sources that include NHTSA, Hemmings, RepairPal, and Hagerty to compile a list of incredibly reliable inline-six engines.

10 AMC/Jeep 4.0

Best Qualities: Excellent Low-End Torque, Simple And Straightforward Design

Jeep's legendary 4.0-liter inline-six engine has its roots in the 1964 232 cu-in engine, which was AMC's first modern inline-six engine. The 4.0-liter engine first appeared in the 1987 Comanche and Cherokee models. Producing 173 hp and 215 lb-ft of torque, it outperformed other V6 offerings from Ford, GM, and Nissan. The engine soon found its way under the hood of the Wrangler and Grand Cherokee in 1991 and 1993, respectively.

AMC/Jeep 4.0 Reliability

The AMC/Jeep 4.0-liter inline-six engine features a simple and straightforward design making it highly unproblematic, very fuel-efficient, and a famous choice for adventure-loving Jeep enthusiasts. When its production finally ended in 2006, the 4.0-liter inline-six was arguably the most unkillable engine in Jeep's history. It was so reliable that it outlived the rest of the car. Insane!

9 Ford Barra

Best Quality: Great Tuning Potential

Introduced in 2002, the Ford Barra inline-six engine earned its rightful place among the greatest six-cylinder engines thanks to the local tuning scene. The engine's architecture can easily withstand over 500 hp while on stock internals and over 1,000 hp when beefed up with aftermarket mods.

Ford Barra Reliability

Producing about 244 hp at its debut, the engine produced 436 hp by the time its production ended in 2016. But stock power isn't the only reason the Ford Barra earned its legendary status; the engine has incredible reliability and can easily run for more than 300,000 miles without major repairs.

8 Ford 300

Best Qualities: Tough Cast-Iron Construction, Simplicity

A staple in classic American trucks, the Ford 300 literally helped build America. It powered almost every man-made machine, from the Ford F-Series trucks, tractors, and irrigation pumps to farm trucks, commercial trucks, and wood chippers. It was a staple for construction workers, farmers, and even lumberjacks.

Ford 300 Reliability

Ford 300 inline-six engines are so reliable that they are literally unkillable. These engines have a reputation for lasting up to 300,000 miles without major issues, thanks to the tough cast-iron construction which makes them highly durable. They put down gobs of low-end torque, making them favorites for heavy tasks. A version of the 300 CID triumphed the Baja 1,000 a remarkable three times – one of the toughest durability tests in motorsport.

RELATED: 10 German Sports Cars With The Most Reliable Engines

7 Jaguar XK6

Best Qualities: Pleasing Exhaust Note, Smooth Operation

Produced between 1949 and 1992, the Jaguar XK6 earned its reputation on both the track and the road. According to Hagerty, the XK6 is "the engine that made Jaguar." It powered not just one but a whole fleet of Jaguar's iconic classic cars, including the legendary E-Type.

XK6 Reliability

Testament to its over-engineering, the XK6 even powered military tanks and vehicles. The engine has a distinctive melodious sound, and its inline-six configuration helps it deliver smooth performance. One of the most reliable inline-six engines, the XK6 featured a seven-bearing crankshaft and a robust cast iron block. On top of that, the aluminum cylinder head took well to aftermarket modifications.

6 Mercedes-Benz OM606

Best Qualities: Fuel Efficient, Potent Low-End Torque

A close cousin to the Mercedes-Benz OM603 engine, the OM606 is one of the best inline-six diesel engines. It packed one hell of a punch regarding torque and was just as durable as the OM603.

Widely renowned for its durability, the OM606 powered the 1993-2001 S-Class, E-Class and Gelandewagen SUV, producing between 134 hp and 177 hp. Still, you can easily coax over 300 hp from the turbocharged OM606 with mild tuning. Many OM606 owners acknowledge the engine is near-perfect, with minimal complex issues.

OM606 Reliability

Mercedes-Benz built the OM606 with an advanced direct fuel injection technology, optimizing combustion and significantly reducing the rate of fuel consumption. This and the engine's torque nature makes for an efficient and potent engine for tough vehicular duties.

5 BMW M88

Best Qualities: High-Revving, Great Power And Torque Output

Despite its short production run, gearheads regard the M88 engine as one of the best six-cylinder engines ever produced. The 3.5-liter inline-six engine found its way under the hood of performance marques, from the classic M5 sedan to the high-performance M1, where it cranked out 282 hp.

While it proved more than capable, whether on or off the track, the M88's ultimate legacy was how reliable it proved to be. Under proper maintenance, these engines can rack up insane mileage. There are many M88s out there, boasting over 300,000 miles.

M88 Reliability

For its production era, the M88 engine was quite advanced, boasting an amazing level of power and torque output. Furthermore, its high-revving character makes it such a potent engine with great racing pedigree.

RELATED: 10 Most Powerful Big-Block Engines Of All Time

4 Chrysler G

Best Quality: Durability

Introduced in 1959, Chrysler's G engine quickly earned the famous 'Slant-Six' nickname due to the engine block positioning that tilted 30 degrees to the right side of the hood. This new design aided easier access to the engine parts and lowered the car's center of gravity.

Chrysler G Reliability

Available in 170, 198, and 255 cu-in versions, the 255 is the one hailed as the engine that refuses to die. The engine's sturdy crankshaft and block contributed to a stout motor that owners found fairly easy to live with.

3 Toyota 3M

Best Quality: High-Revving

Toyota stepped into the world of high-performance cars with the 3M inline-six engine built in collaboration with Yamaha. Specifically built for the iconic Toyota 2000GT, Yamaha added two-barrel Solex carburetors and an aluminum DOHC cylinder head to the original M block. The result? A 7,000 rpm-redline, incredible performance, and bulletproof reliability.

3M Reliability

Producing 148 hp and 129 lb-ft of torque from the 2.0-liter naturally aspirated inline-six engine, the 1966 2000GT went ahead to dominate the racetrack, including winning the Fuji 1000 Kilometers race and the 24 Hours of Fuji. Today, the 2000GT is among the most iconic and sought-after classic cars, thanks in part to the unkillable 3M inline-six motor.

RELATED: 10 Most Reliable Ford Engines Ever Built

2 Nissan RB26DETT

Best Qualities: Robust Power Output, Great Tuning Potential

The RB26 is the holy grail of Nissan's RB-series engines. Dubbed the Godzilla engine, the RB26DETT produced jaw-dropping performance and inhibited tremendous tuning potential.

RB26DETT Reliability

Producing 276 hp in stock form, 500 hp from the RB26DETT isn't an overstretch, all while on stock internals, thanks to the sturdy aluminum cylinder head and cast-iron block. The 2.6-liter twin-turbo inline-six engine powered the iconic Skyline GT-R R32, R33, and R34, which are some of the best tuner classics today.

1 Toyota 2JZ-GTE

Best Qualities: Takes Significant Modifications And Power Upgrades With Ease

Toyota has built some incredible engines over the years, such as the rev-happy Lexus LFA V10 engine, but none is as desirable as the legendary 2JZ-GTE. The 2JZ-GTE was Toyota's answer to the RB26DETT, and boy, the engine was a true engineering marvel.

2JZ-GTE Reliability

Bolstered by a cast-iron block, the 2JZ-GTE engine is not just reliable, it is indestructible. On top of that, power junkies and street racers found ways of getting over 1,000 hp from the engine by adding boost and other aftermarket mods, making the 2JZ-GTE the prime choice for swapping into other cars.