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After more than 50 rentals, my grandpa and grandma have noticed that Enterprise CarShare's cars match manufacturer's advertised fuel economies, but Enterprise Rent-A-Car's are much lower:

As an example:

  • a CarShare's Kia Soul yielded 4-6 L/100 km, but
  • the same vehicle with Rent-A-Car's yielded 13-15 L/100 km!

They suspect that as CarShare (a car-sharing company) pays for gasoline, it cleans and services their cars better than Rent-A-Car, which requires renters to pay for gasoline and so has less incentive to keep cars fuel-efficient.

They drive identically on CarShare's and Rent-A-Car's cars. If anything, they'd expect worse fuel efficiency for CarShare's cars especially in the winter when they use the car heater.

  1. Is there any evidence for our suspicion? Has anyone experienced this difference?

  2. If our suspicion is true, then please see the question in the title. Starting with a fuel-efficient car is easier than requesting compensation after the trip.

  • Are the cars the same age? Have they been driven the same by other drivers? Are they maintained to the same standard? – Solar Mike Nov 22 '18 at 10:38
  • If you are talking about the same model and engine, the 13-15 L car was surely broken. Report it to the Rental! – Daniel Nov 22 '18 at 18:32
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In direct answer to your question "How can you guarantee that your rental car won't use unreasonable more fuel?", the simple answer is; You can't.

What Car magazine have done extensive research and testing into the differences between manufacturers published fuel consumption figures and the real world figures drivers actually achieve. This link provides access to extensive information on this.

The figures you've quotes for the two Kia Soul vehicles, how were these obtained? If these are accurate they'd suggest something is wrong with one of the vehicles assuming they are the same model, year and engine spec.

Some ECU's adapt their mapping based on how the vehicle is driven. Alfa Romeo for example, sharpen the throttle response for cars where the recent driver data shows they are being driven enthusiastically. This could be a factor when comparing rental cars which do this based on what the previous drivers did with them. However, this wouldn't account for such vastly different figures.

Things like checking that the cars tyres are inflated properly, fluid levels are correct and that there are no obvious signs of mechanical issues such as a noise from a dragging brake or a mis-firing cylinder (we experienced this on a 26 mile, brand new Nissan hire car once). If you find an issue on initial inspection, go back to the hire desk and explain. They'll usually swap you onto an alternative vehicle or rectify the issue. Beyond that, there really isn't anything you can do to guarantee that you'll achieve anything like the manufacturers published figures other than driving gently, avoiding traffic, avoiding idling and trying to plan routes ahead of each journey.

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