A diesel engine is one of biggest changes to be stoked about for the next-generation . We know for the car, and now we’re seeing that Jeep appears to be testing it on a prototype of the hardcore off-road Rubicon.

Our friends at sent over some spy pictures of a development mule Wrangler with the Rubicon’s red struts, knobby tires and Dana 44 solid axles. Oh yeah, and that giant “RUBICON” sticker on the hood. It also had a diesel exhaust fluid tank, leading to the conclusion that Jeep is planning to put their diesel engine in the Rubicon.

Diesel exhaust fluid (usually called “DEF” or “AdBlue”) is a liquid mixture of a chemical called urea and special water that’s injected into a diesel engine’s exhaust stream to effectively convert noxious emissions into simple nitrogen and water.

As the most capable trim level of probably the most capable off the shelf off-road vehicle in America, the Rubicon getting an oil burner is a big moment for fans of torque and recreational four-wheeling.

As to what specific diesel engine Jeep will go with for the next Wrangler, the JL Wrangler Forum folks it is “all but assured to have the 3.0-liter VM V6 diesel engine expected to be paired with the 8HP75 transmission.” That’s the same diesel power-plant used in the Ram EcoDiesel and and Jeep Grand Cherokee EcoDiesel, so the assumption is logical.

I know some of you will be bummed that there still isn’t much talk about a diesel manual Wrangler in the rumormill, but it’s cool to see that the company is trying to pair it with the 4x4's enthusiast-spec and not just stick it in some random trims.