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I'm currently driving a Suzuki SX4 2008. It gets (supposedly) 30 MPG (9.4 l/100km) on highways, though I suspect it's much lower now because of the beating I have given the poor car and lack of proper maintenance.

I regret the choice because I turned down a cheaper more fuel-efficient vehicle for it when I purchased it. At the time I had not anticipated how much driving I would be doing (a side effect of volunteering). I did over 15 hours of driving last week, almost exclusively highway. My usual week isn't quite that bad, but I do 30 minutes per day for work, and probably at least 3-5 hours a week for volunteer activities, likely more. A more fuel-efficient vehicle will definitely help. I'm considering either an electric or a tiny two-seater for my next vehicle, depending on how much they actual cost to purchase.

However, replacing a car has an environmental impact as well. The cost of building a new car releases a significant amount of pollution. I'm trying to figure out how the harm of purchasing a new car weighs against the harm of the pollution of an older, less fuel efficient, and poorly maintained vehicle. I figure keeping the old car would likely work out as environmentally better, but by how much?

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    Since you're (presumably) going to sell your car to someone else, that needs to be factored in somehow - your old car might go to someone who drives less. I'm not sure an electric car will work for you -- 15 hours of driving in a week means at least 2 hours/day, or over 100 miles at highway speeds - most mainstream EV's (excluding the $80K Tesla) have a range around 80 - 100 miles, so unless you can charge while on the go, you may not have enough range in an EV.
    – Johnny
    Dec 8, 2014 at 16:54
  • Yes johnny, I misspoke. I should have said hybrid, not pure electric. I drive up to 6 hours a night on nights when I volunteer so range is an obvious concern. I Haven't gotten to the point of considering actual vehicles or their viability yet, I'm still trying to decide if I should even consider replacing the vehicle yet; and I'm leaning towards no :)
    – dsollen
    Dec 8, 2014 at 19:52
  • What about taking it for a tune-up? This will be cheaper than a new car and can improve fuel efficiency, though it's hard to say by how much.
    – LShaver ♦
    Jul 29, 2018 at 16:15

2 Answers 2

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+100

According to this reference, up to 12 - 28% of the carbon emissions associated with a vehicles life cycle come from its manufacture and delivery.

So starting right now, of the two vehicles, the new one has a much larger impact than the old one. It would take a considerable amount of "better mileage" to overcome that impact. And that doesn't even factor in the impact of disposing the old vehicle - or that if you don't dispose of it it will continue to have an impact when driven by someone else.

If you're driving an oil burning, coolant leaking beater the argument might be different.

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This is more of an elaborate comment on the answer by the user "That Idiot" to demonstrate how we can do calculations on these things.

Using this resource (sorry, in Dutch), I assume…:

  1. a car has cost already 3800 liters (1000 gallons) to get produced.

  2. the PO's "CO2"-Karma is reset to 0 at the moment we start our analysis.

  3. Using the metric system instead: [ I assume ] the PO's current car uses 1 liter of petrol per 10 km, and a new fuel efficient car uses 1 liter of petrol per 20 km.

  4. the only environmental impact of a car is it's CO2 impact. (it's not)

  5. the impact of disposing a new car can be neglected (it can't)

I can now create a graph with the liters of fuel used on the Ordinate (y-axis) and the kilometers traveled on the Abscissa (x-axis). The current car is represented by the red line, the new car is represented by the green line. The vertical blue line represents the amount of kilometers after which the burden of producing a new car is compensated by the new car's better fuel efficiency. This is around 78000 km or 50 000 miles (!) This might indeed be between 5 and 10 years of use.

The old car has already been produced ages ago and is approaching it's end-of-life, so this line starts at the origin. (That's what I mean with the PO's CO2-karma is thought to be reset at the moment of analysis.) The new car is produced as a result of the PO's wish to buy a new fuel-efficient car, and starts it's life with 3800 liters of fuel already used. enter image description here

* DISCUSSION *: the 3800 liters mentioned seems to be for a Prius. I believe a conventional small car like a VW-UP might take considerably less to produce.

* REQUEST: If somebody could help getting these numbers more accurate,... then: please :)*

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  • While the jury is still out on this, EV's may well last much longer than IC vehicles, given reasonable body construction.
    – Sherwood Botsford
    Mar 10, 2021 at 21:53
  • There is also a virtue value of postponing a new vehicle, especially if you are a low mileage user. If you don't buy it, it's available for a high usage person to buy. In addition the range/winter usage issues may mean that the best option is to own two vehicles, an IC vehicle with winter tires on it for cold weather use, and an EV for the other three seasons.
    – Sherwood Botsford
    Mar 10, 2021 at 21:56

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