GM had big plans for a half-ton diesel powerhouse—the 4.5L Duramax V8. It promised 310 horsepower, 510 lb-ft of torque, and a whole new era for diesel trucks. Then, the Great Recession hit, and GM killed the project before it could hit the road. Or so we thought. Turns out, at least two prototype engines survived. Someone had them, and they were willing to talk. Then—just as suddenly—they weren’t.

As Caleb Jacobs over at The Drive reported, “someone sent me a message request on Facebook,” and when he accepted, he was greeted with two photos. No introduction. No context. Just images of what looked like a 4.5L Duramax prototype. When he asked, they confirmed it—“Not only that, but they had two in their possession.”

This was big news. The 4.5L Duramax, also known as the LMK, was supposed to be GM’s answer to Ford’s Power Stroke and Ram’s Cummins. A small but mighty diesel V8 built for half-ton trucks. But the project was axed, and surviving prototypes were thought to be locked away or scrapped. Yet here they were.

The 4.5-liter Duramax V8s disappear again

Jacobs continued messaging with the owner, learning that they “acquired both Duramax prototypes in a bulk purchase.” But they wouldn’t say where from or who sold them. The engines weren’t in running condition, but the owner hoped to sell them to someone who could bring them back to life.

Then, everything changed. After a few days of radio silence, Jacobs followed up, even offering anonymity. That’s when the owner went “full ghost mode and unsent their previous messages.” Suddenly, the conversation was wiped clean, as if it had never happened.

It’s not every day that long-lost GM prototypes show up, and it’s even rarer for them to disappear just as quickly. Jacobs noted that in seven years of reporting, he had only seen this happen “a handful of times.” But why? Were they afraid GM would come knocking? Did someone else step in with a better offer? Or did they just get cold feet?

GM’s 4.5L Duramax V8 could have changed the truck world. Instead, it was scrapped before its time. Now, two prototypes have surfaced, only to be shrouded in secrecy once again. Whether they’ll ever make it into a truck—or even see daylight again—is anyone’s guess. But one thing’s for sure: these engines still have a story to tell.