It definitely makes more sense from a green perspective to keep your old car running and well-maintained as long as you can—especially if it’s getting such good mileage. There are significant environmental costs to both manufacturing a new automobile and adding your old car to the ever-growing collective junk heap.
Does Better Fuel Economy Guarantee a Greener Lifestyle?
A 2004 analysis by Toyota found that as much as 28 percent of the carbon dioxide emissions generated during the lifecycle of a typical gasoline-powered car can occur during its manufacture and its transportation to the dealer; the remaining emissions occur during driving once its new owner takes possession. An earlier study by Seikei University in Japan put the pre-purchase number at 12 percent.
Regardless of which conclusion is closer to the truth, your current car has already passed its manufacture and transport stage, so going forward the relevant comparison has only to do with its remaining footprint against that of a new car’s manufacture/transport and driver’s footprint—not to mention the environmental impact of either disposing of your old car or selling it to a new owner who will continue to drive it. There are environmental impacts, too, even if your old car is junked, dismantled and sold for parts.