I ask because my Sim has been working on it for ages~ she has level 10 handiness skill but still has the 'work on engine' option and there's no option to paint it either.
Carl's Sims 3 guide says it takes 14 hours to "complete" the car, but it's been way longer than that and it still isn't done. Like, my Sim can drive it, but wax and work on engine are both still options (which they shouldn't be, if it's done).
Other than that one little tidbit from Carl's, I can't find anything about this specific issue anywhere. No one else seems to have issues with this item, and I'm not sure if (maybe) I'm getting the car confused with a similar one from Sims 2.
I didn't find the right solution from the Internet.