I am personally goal motivated: I like achieving and building things (I enjoy the process in as much as I got the better of it :)). When things are complex, I come up with smaller goals that are on the path to getting the big thing done, all the while thinking how these things fit together.
This has made me great at coming up with iterative steps where each step brings value: even if I stop at any one point, I have done something useful.
In your example, I would probably dismantle the car enough to get the engine out and rebuilt and back in, and then go back to it sometime in the future to work on other stuff, all the while keeping a functioning car as I am rebuilding it.