THERE ARE ONLY TWO STRAIGHT SIX DIESEL ENGINES LEFT
Though automakers like Stellantis, Mazda, BMW, and Mercedes-Benz are keeping a few straight-six engines alive in 2025, there are currently just two straight-six diesel powerplants left on the market. Both of them are American, and both are in pickup trucks. Below, we look back at the history of each, as well as their modern-day technical feats and specs, along with the vehicles they power and what you should expect to pay for one today.
Diesel engines used to be a lot more popular. These days, they're increasingly rare as hybrid gas engines are emerging as the solution some drivers want. Six-cylinder engines were once much more popular as well. These days, they're mostly been replaced by turbo fours. In fact, back in 2024, we ranked every inline-six engine still on sale by horsepower. On that list, you'd find just two diesel engines, which are the subject of our feature below.
Meet Your Two Straight-Six Diesel Choices: Cummins Vs. The Baby Duramax
The first of our endangered engine species of the day is the LZ0 Duramax, formerly known as the LM3 Duramax. This 3.0-liter turbodiesel straight-six engine is used in various GM SUVs and pickup models, including the Tahoe, Silverado, and Sierra. For other markets, this engine is available in 3, 4, and 5-cylinder configurations. It was launched for the 2019 model year on the Sierra and Silverado 1500 pickups. Still, it was not immediately available in Trail Boss models because the length of the new straight-six engine didn't quite clear the internal bumper design of that particular truck. This issue was addressed with a later modification.
For the 2023 model year, a revised engine (now called LZ0) replaced the original, previous-generation LM2 unit, providing better power, torque, towing, and cooling system performance. Specifically, engineers made key component upgrades, including new pistons with an improved combustion bowl, a retuned turbocharger, new fuel injectors, and 'improved temperature control features'. Additionally, the latest upgrades include a recalibrated air intake and sound-deadening measures, making the engine even quieter than ever. This coincided with increased availability of the diesel engine in higher-end trim grades where a more refined drive was required. You could even get this engine in the Cadillac Escalade.
In terms of fuel economy, using the Yukon with a 5.3-liter small-block V8 as the baseline, the optional straight-six diesel engine delivers a significant torque advantage while consuming approximately 35% less fuel on the highway and about 40% less in the city. Owners sometimes call this engine the 'baby Duramax', a smaller alternative to the Duramax V8 turbodiesel engine from the HD model range, with more than twice the displacement. It doesn't have the angry, high-revving pull of the 5.3-liter, but the torque at low revs is effortless, generous, and quiet.
The Duramax straight-six engine comes standard with a 10-speed automatic transmission, as do the other engines offered throughout the GM truck and SUV range. The choices also include a 5.3-liter gas V8, a 6.2-liter gas V8, and a 2.7-liter four-cylinder gasoline turbo engine, known as the TurboMax. These four engines comprise the current-day mainstream GM 4x4 lineup, offering shoppers a range of options to consider, encompassing 4-, 6-, and 8-cylinder configurations, as well as both gasoline and diesel power. With the straight-six diesel on board, owners have an option with the torque of a big V8, but not the monster gas bill.
Next on our list is the second of your two remaining straight-six diesel engine choices: the Cummins 6.7-liter Turbo Diesel. You'll find this enormous straight-six under the hood of various heavy-duty Ram trucks, and other variations of this engine create the soundtrack to daily school-bus rides across the country. For Ram 2500 duty use, the latest version of the Cummins Turbo Diesel arrived for the 2025 model year, featuring improved refinement, efficiency, cold-start performance, and easier maintenance. This represents the latest advancement to the engine, part of a decades-long development partnership between the two companies.
The new 20255 engine features a redesigned block and cylinder head, robust new heavy-duty pistons, a new performance intake manifold, a variable geometry turbocharger, larger intake/exhaust valves for improved port flow, and a higher-pressure fuel system. The new Cummins Turbo Diesel engine boasts 36,610 pounds of towing capability, paired with a more fuel-efficient 3.42 rear axle ratio. Max towing was previously available only with a 4.10 axle ratio. The engine and axle upgrades also shave 1.1 seconds from the 0-60 sprint, now achieving a time of around 6.9 seconds. Performance attracts shoppers to Ram showrooms, which is why this high-output diesel packs a whopping 1,075 lb-ft of torque and has historically been a major part of the diesel power wars waged between the Big Three automakers in the HD scene.
Like GM's straight-six turbodiesel engine, the Cummins engine is an added-cost upgrade.
Here's What You're Paying For A Straight Six Diesel Today
Let's take a look at what you'll pay for a new or slightly used straight-six diesel pickup today. When making your decision, note that choosing a nearly new truck with very low miles can save you thousands upfront, thousands more on fees and destination charges, and leave you with almost the entire factory warranty coverage remaining.
We'll go with the Duramax first. Brand new, you'll be paying at least $54,445 for the Duramax-equipped Silverado 1500, or around $71,120 for a Duramax-powered Tahoe. In the used market, data from Autotempest.com shows that plenty of high-mileage used copies are available for around $22,000, commonly with 100,000 miles or more on their odometers. From the mid-thirties, you'll find plenty of Duramax-powered units with sub-40,000-mile odometer readings. With that same engine and odometer range, a used Chevrolet Tahoe from 2019 onwards will run you closer to $60,000. You can get a Duramax-powered Escalade for that same sort of spend, but most units have odometer readings past the 70,000-mile mark.
That's approaching the brand-new cost of the second engine choice on your page: the latest and greatest Cummins. The least expensive way to get into a truck with this engine is via the Ram 2500 Black Express, which comes with an optional $12,995 Cummins upgrade, for an MSRP of $65,105, to start. For that sort of money, you could also consider a slightly used 2025 model year Ram 2500 from a higher trim grade, such as a Laramie with 10,000 miles on the odometer, for instance. Trucks from the 2024 model year and earlier, with the pre-update version of this engine, are even more affordable but have a shorter remaining warranty.
Be Careful Filling Up Your Tank, And Note This Important Tip
Sometimes, when driving your new diesel truck, you go to the gas station to refuel and accidentally forget that it doesn't run on gas. Though it's not easy to get gasoline into the tank of a diesel-powered vehicle, people inevitably succeed in misfueling their vehicles all the time. If you accidentally pump gasoline into your diesel truck's fuel tank, regardless of the quantity, the following information could save you tens of thousands of dollars, so read it carefully: do not start your engine. Instead, call a tow truck, and be sure the driver doesn't try to start the engine either.
Filling a diesel tank with gas sucks, but it's not the end of the world. The tank can be drained, flushed, and used again. If you accidentally start your engine while there's gas in the fuel tank, you'll infect tens of thousands of dollars' worth of hardware, sensors, and equipment in a matter of seconds, possibly turning your engine into a boat anchor. Keep this in mind whenever you, or anyone else, are refueling your truck.
2025-10-11T07:39:53ZSources: GM, Stellantis, Autotempest
