I’ve seen a lot of posts and comments around teh intarwebs which interchangeably use the terms “mule” and “prototype” for any car or truck with a manufacturer license plate, so I thought I’d clear it up a bit.

a mule is a kind of Frankenstein’s monster of a creation. Mules are usually cobbled together from existing production vehicles, but cut apart and modified so they can accept whatever parts or subsystem the automaker wants to test. For example, the mules for the 2011 Explorer looked like this:

These were Freestyle/Taurus X bodies cut in half, widened, and adorned with a Flex front clip in order to test something “under the hood” (engine, trans, cooling, whatever.) Mules are meant for very (very) early testing of new tech, and get junked pretty quickly. GM was testing the Voltec powertrain in Malibus and Saturn Auras which looked like this:


On the other hand, a “prototype” is a design-intent vehicle built well before volume production begins. The first stage is slow-built by hand in an engineering facility, but they are of the final design and are what engineering use for validation testing. An early/slow-build prototype typically has very heavy camouflage like this:


Later prototypes built at the targeted assembly plant will have less camo but still have the main features covered:

If you see a car or truck that looks like a regular car or truck, but with a manufacturer plate, it’s probably not a “mule” or a “prototype.”  it’s probably just a regular production vehicle, used for certain purposes like press/media cars, pool vehicles, whatever.