In many ways cars are better than girlfriends -- you can get in whenever you want, they don't complain when you take their tops off, and spare tires are actually a plus. To follow up on old flames that could be covered in them, hit up Check My Ride
A recently launched social network affiliated with a major auto data company, Check My Ride lets you build and share a comprehensive personal vehicle history and check up on old whips using their "Where in the World is My Car?" tool, not to be confused with the Dude Where's My Car? tool, as no one cares where Stifler is (spoiler alert: it's rehab). Start by building a detailed history of your vehicles (age when purchased, year/make/model/color, year sold, etc.), including awesome road trips you took, how many miles you put on, and "why [it] was memorable"; once complete, it'll calculate the total mileage you've accrued since you started driving and generate a bar graph timeline of your life in terms of car ownership, which will be low if you're wont to take "bar graph" literally. Next, enter a VIN into the car-finder widget (powered by AutoCheck) to see deets on an old whip's current whereabouts, including a GMap with connected pins showing the places it's been registered since you ditched it, unless you literally ditched it, in which case, um...it's in a ditch
You can also connect with fellow users to comment on their cars, and, once membership levels are a bit more robust, possibly even track down your old ride's current driver, who hopefully isn't referring to your ex-girlfriend when he starts talking about burning rubbers.