The Prius Lies

By Deane Barker on June 12, 2008

Toyota Prius vs Jeep Patriot: the great MPG test: Apparently the onboard computer in the Prius lies through its teeth. These folks did a test between a Prius and a Jeep Patriot. At the end, the Prius claimed 57 mpg. Then they checked actual fuel levels to see how much had been used:

The result was astonishing: both cars had used nearly identical amounts of fuel. The Jeep had averaged 38.9 mpg – only 3.1 mpg less than its computer had recorded. However, the computer of the Prius appeared to be telling whoppers: it actually achieved just 39.9 mpg – a massive 17.1 mpg less than it had claimed.

I maintain that the Prius is something of a crock. Though it did get us all thinking green, this thing isn’t close to as wonderful as they all claim.

Update: This article claims that this test is flawed. Due to the type of fuel tank used by the Prius, the method they used to calculate real-world mileage is invalid, the article claims.

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  1. I wonder how many Prius owners actually check the accuracy of the onboard computer’s fuel efficiency calculations. I bet everybody who reads that article will be doing that now.

  2. I have been looking at hybrids and always wondered about the Prius numbers.

    The Nissan Altima Hybrid states 35 MPG city, 30+ highway and a friend who has one gets nearly those numbers with careful driving. The Prius and the Altima Hybrid have similar weights I believe so I wondered if the Prius was inflating the numbers.

  3. The testers couldn’t select drive let alone operate the computer. Not too confident how they would handle a calculator either. Well they probably did not reset the mpg after fillup or they reset it before fillup. The mpg is no longer reset automatically at fillup btw. If that does not make sense to you then you could be one of the many who winge about the computer being inaccurate when it is operator error to blame.

  4. Not sure why you keep knocking the Prius… I have one, and it gets the gas mileage it claims. It is a great deal, under $30K for a fully loaded and VERY comfortable car. I switched from a Mercedes E55, and am glad I did. I average 45MPG with it, and I have verified this between fill ups. I live in Silicon Valley, where the gas is currently averaging $4.60/gal for regular. Maybe it is cheaper where you live? I’ll take a Prius any day over anything else!

  5. 30K fully loaded? Holy hell! My 06 Jetta TDI is fully loaded and I paid $20k for it. That’s already $10k less. That and considering I get the same fuel economy even when I’m not nice to it. My best tank average has been 52 mpg and that’s a lot for an automatic.

  6. Where did you get a Jetta TDI for $20k? I call shenanigans.

    I like my Prius. If I went your route I’d have to drive a VW. No thank you…been there, done that. Those cars are garbage.

  7. Mine lies, but not by much. I have checked 6 consecutive gas tanks, using only the gas receipt and the odometer only to figure MPG. When I compare that to what my Prius usually says, mine always reports better mileage than I get, but only by 2 to 3 mpg. E.g., I usually hit around 46 MPG but it says 49.

  8. My 2007 Prius lies like crazy. I never get to 400 miles on a 10 gal refill, but the onboard computer constantly claims 44+ mpg or better. I’m usually refilling by 370 miles or so. OK; that’s only a 15% error, but, still, where does that error come from? The computer should be dead on! The computer needs to know the precise gasoline amount to inject for the engine. Wonder if this is an example of error caused by alcohol in the gas? Gasohol is less than 90% as efficient, so perhaps the car gets 10% less energy and 10% fewer miles per gallon of gas? Still, doesn’t the Prius’s computer need to sense the energy density and compensate with more fuel?
