The cat was smart enough to not actually get into the engine compartment, but a space over (and separated from) the wheelwell behind the front quarter panel. Unfortunately, he was not quite clever enough to get back out of that spot, so he spent the rest of the weekend in there after we discovered his predicament late Saturday night.
Vogon took the car into the shop this morning where they extracted a muscular short-haired brown tabby from the car and put him into a box for transport home. He was quite grateful when I let him out into confinement in the master bathroom with a freshly cleaned litter box, bowl of dry food and bowl of water.
The cat has no collar and is uninjured save for a spot on his front left leg that I cleaned up with peroxide. He does not have as large a vocabulary as Biko, so he has not said much yet except to tell me the food is dry and that he wants out of the bathroom. Biko has been sitting in the bedroom all morning peering at the master bathroom door.
I've put together a found flyer to post and e-mail to local animal shelters, but if we wind up keeping him, he will be named Fender.
edit 1605: We just got our first call from a lost cat owner. They live about five miles away and across the Tollway, but I wouldn't put it past a cat to get that far in a week. We're meeting later today to see if it's their cat.
edit 1800: He wasn't her cat. She suggested that I list him on Tabby Tracker as a large found cat. Done and added to my list of places he's been listed as found.