The Cummins 5.9-liter inline-six diesel engine is said to be one of the best full-size diesel engines produced thanks to its renowned reliability. Some might even say it's invincible, but this engine teardown video from I Do Cars says otherwise.

So what can really kill a Cummins diesel engine? Eric, the presenter of the video below, pulled the engine from a 2004 Dodge Ram 2500. It was completely locked up, and the goal of the teardown was to determine the cause of why the crankshaft couldn't turn.

Eric believed the diesel mill used to generate 325 horsepower and 600 lb-ft of torque when it was still running. Of note, Cummins has been powering Ram trucks since 1989, which cemented the brand's notoriety among truck enthusiasts.

While stripping parts one by one, the host spotted something he hasn't seen before in his years of salvaging automotive power units. The oil filter was completely dry, which sounds bizarre considering other components were still lubricated or contained water.

Further in the teardown, it wasn't until the crankcase was accessed that he saw progress, pointing out that the worn connecting rods and rod bearings could be the root of the issue.

After removing some of the pistons, the crankshaft started to turn. Eric was surprised to see all the components looking better than expected, especially considering how intense that lockup was. The host admitted that diesel engines aren't his forte, but we learned plenty from the 44-minute teardown video.

Ultimately, the damages on cylinder three were marked as the major cause of the engine failure. The damages probably stemmed from high engine operating temperature and pressure over time. There were also broken compression rings, as well as wear on the crankshaft and other cylinders.

Eric also works on gasoline engines, including the SkyActiv engine teardown pulled from a Mazda CX-30, which was said to be already dead at just 30,000 miles.