If someone tells you to skip the new trucks and look for something older, something with proven reliability, selling at a low price, that's good advice. Unfortunately, if we're talking diesel, it's getting harder and harder to find old Ram 2500s and Ford F-250s cheap. Put simply, the people who own these trucks know exactly what they've got.You can blame a combination of emissions regulations, Dieselgate, and the plain fact that they don't make them like that anymore. Let's Take A Look At The Used Diesel Market Ford To see what we're talking about, let's compare some used diesel trucks to their gas-powered siblings.Based on typical listing prices for models in the 150,000-mile range, diesel-powered trucks uniformly sell for at least a few thousand dollars more than their gas-powered twins. In some cases, the difference is pretty dramatic.Check out the 2015 Ram 2500 SLT with four-wheel drive. That one's powered by a Cummins 6.7-liter turbodiesel V8, sort of a holy grail among diesel buyers for its longevity and power delivery. With diesel power, you're looking at a difference of $9,480, with everything else being equal. Same condition, same mileage, same options, but add a Cummins to the mix, and you're spending nearly $10,000 more on the purchase.To get an idea of what typical depreciation looks like for gas versus diesel, we can take a look at a 10-year-old Ford F-250 and see how the prices shake out. Back in 2016, the addition of a 6.7-liter Power Stroke Turbodiesel V8 would have been an $8,480 upgrade, which gives us the following numbers...At a glance, the difference in depreciation looks fairly marginal, but consider that the diesel is still commanding a $5,900 premium over the gas-powered variant after 10 years and 150,000 miles. Bearing that in mind, the engine itself is still worth 70% of its initial option price. It's A Seller's Market Out There Stellantis Ultimately, older diesel trucks bear all the characteristics of a seller's market. The primary driver is, of course, buyer demand. To take it from diesel fans themselves, a user in the r/Powerstroke subreddit says of the 2011 6.7 engine "I'm at 300,000 miles, and my boss has a 2011 with 600,000 miles, all original everything."A 6.7 Cummins owner claims 340,000 miles before the first breakdown, in the r/Cummins subreddit, and one driver reports a 2005 model with 600,000 miles on the odometer.It's difficult to find a bad review or a reliability horror story when it comes to these older diesel engines. Buyers want them, and owners are hesitant to part with them. Add that to proven reliability well past the point where a gas engine would have given up the ghost, and a timeline of increasingly restrictive EPA regulations, and you have a perfect recipe for high resale prices. The EPA Has Certainly Played A Part In Driving Diesel Prices Up Ram To some extent, you can tie the slow depreciation of diesel-powered pickups to increasingly tight EPA emissions laws. DPFs, or diesel particulate filters, became standard in 2007, for instance, intended to trap black carbon soot, ensuring cleaner exhaust emissions. Many truck owners swear by pre-2007 engines like the LBZ Duramax, for this reason.2027 will bring another major choke point, with the EPA dictating that new engines for commercial applications must reduce NOx emissions by roughly 90% below current limits. This primarily affects big rigs and the like, but is expected to have a ripple effect on light-duty trucks.It wouldn't be accurate to lay this all at the EPA's feet, though. The demand for diesel-powered work trucks in fleet use and rural areas plays a part, and there's the simple fact that, because diesel trucks are so reliable, owners keep their trucks for longer, meaning there are fewer used models available to begin with, meaning prices stay nice and high, because buyers don't have a lot of options. New Diesel Purchases Are Down, Too Ram According to data from Alan Baum, Baum & Associates, Ford sold 89,540 diesel-powered pickups in the first quarter of 2026, compared to 112,454 sales for Q4, 2025. It's the same story for Ram and Chevrolet. Ram sold 25,716 diesels in Q1 to 30,342 for the end of 2025. Chevy sold 24,933 units in Q1 to 31,853 in Q4 last year.This is only looking at a six-month stretch, but it's certainly indicative of a broader trend that you can trace back for years. In 2006, diesel made up around 8% of light-duty truck and SUV sales (diesel passenger cars were practically unheard of in the US, even then, and are even rarer now). In 2026, that number may be closer to 3%.Again, this lack of demand is driven, in part, by the perceived longevity of the powerplant, owing to characteristics such as the following. More robust engine blocks and components, to withstand higher compression ratios and hotter combustion. Diesel fuel acts as lubrication, ensuring smoother operation. Older diesel engines have had the time to prove their dependability, frequently packing on half a million miles and more. Diesel engines typically run at lower rpm, meaning that the moving parts are doing a lot less moving. Spark plugs are not required for diesel engines, meaning one less part to replace. The demand for older diesel engines is compounded by a relative disinterest in newer diesel powerplants, owing in part to EPA-mandated technology like DPFs, and the fact that so many modern diesel engines are turbocharged.One user in the r/CarTalkUK subreddit states "Honestly wouldn't touch a diesel in the last 10–15 years." Another states that old diesel trucks are reliable, as a rule, but newer diesels "with DPFs and multiple turbos" are less dependable.Give it another five years, and we may eventually discover that modern diesel engines are just as dependable as their predecessors, and that a DPF won't adversely affect longevity as long as you keep it clean. But the market is driven by perception. The perception is that new diesel engines simply aren't as dependable.There may be some truth to this perception, but it's specifically the perception that's really driving older truck prices up, and limiting demand for new diesel pickups, creating a vicious cycle. People who own older diesels won't part with them, making them more expensive, and contributing to the perception that new diesel trucks are best avoided. Is Now The Right Time To Buy A Diesel Pickup? Ford If it's running on a 6.7 Cummins or a 6.7 Powerstroke or a Duramax V8, there's really no bad time to buy an old diesel pickup.If you're worried about missing out on peak value return, then yeah, you missed the boat. The best time to buy a 2011 Ford F-250 was in 2011, if you want to get the most miles out of the truck for the least amount of money. But, since that ship has sailed, it's like the saying that "it's never too late to start moving in the right direction."These engines are still as reliable as they've ever been, and the sooner you get out there and buy one for yourself, the less time the current owner has to put more miles on the odometer.Our advice: don't stress about "missing out" on the perfect investment opportunity. We're talking trucks, not stocks and real estate. The value that you're going to get out of a diesel engine is going to be tens of thousands of miles of heavy-duty work and highway travel.