Autoblog and Yahoo may earn commission from links in this article.Was This Another Fifth-Gen Cummins Failure?The 6.7-liter Cummins diesel is among the top powertrain picks for the Ram 2500 HD, earning it a considerable following. But the fifth-generation version hasn't exactly been spotless. Owners have complained about valvetrain issues, with teardowns revealing wear on rocker arms and lifters, as well as lubrication issues.So when a dead 2025 Ram 2500 with barely 13,000 miles on the clock rolled into Dave's Auto Center, you can bet everyone was wondering: is this just another chapter in the fifth-gen Cummins saga, or did something even stranger take it out? That's what this video aims to find out.The Real CulpritThe low mileage made the whole thing even weirder. Usually, if an engine's got a design flaw, it gives you a few warning shots before throwing in the towel. For this truck to tap out so early, something else had to be going on. Time for the shop to play detective.AdvertisementAdvertisementIt didn't take long for the techs to realize this wasn't your run-of-the-mill Cummins disaster. The owner had made the ultimate diesel faux pas: filling the fuel tank with Diesel Exhaust Fluid (DEF) and then driving on, blissfully unaware, until the truck gave up. By the time it limped into the shop, DEF had made its way through the entire fuel system.Pulling the fuel filter revealed a horror show: thick, gooey sludge and crystals everywhere, courtesy of DEF and diesel mixing where they absolutely shouldn't. Since the truck had been driven until it flatlined, there was real worry that the mess had already invaded the high-pressure fuel pump, injectors, fuel lines, and maybe even the engine.To see if the engine would survive, the team ran compression tests and scoped out the cylinders. Against all odds, the results looked good. Strong compression everywhere, and no glaring signs of piston or cylinder wall carnage.There were still traces of contamination, but the engine seemed to have escaped total disaster. The fuel system, though, was toast. Fixing the mess would set the owner back close to $50,000, thanks to all the pricey parts that needed replacing on a truck that was barely broken in.Dave's Auto Center/YouTubeA Costly Lesson for Diesel OwnersFortunately, the insurance company took one look at the repair bill and decided to pull the plug, totaling the truck even though it was young.AdvertisementAdvertisementLet this be a cautionary tale for diesel owners everywhere: if you ever put DEF, gasoline, or anything else that doesn't belong in your diesel tank, stop right there and do not start the engine. Once that contaminated fuel starts making the rounds, your repair bill will skyrocket faster than you can say 'tow truck.'Sure, if you own a fifth-gen Cummins, you should still keep an eye on maintenance and those infamous valvetrain quirks. But as this story proves, sometimes it's not a factory defect that takes your truck out of commission. Sometimes, all it takes is a split-second mistake at the pump to park a nearly new Ram for good.StellantisView the 4 images of this gallery on the original articleThis story was originally published by Autoblog on Jun 22, 2026, where it first appeared in the News section. Add Autoblog as a Preferred Source by clicking here.
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