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Prius Owners Question Mileage Claims

By Joe Benton
ConsumerAffairs.com

November 20, 2005

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A desire for fuel economy is the reason most consumers plunk down big bucks for a Toyota Prius or one of the other gas-electric hybrids that are consuming a fast-growing slice of the American auto market.

But while most hybrid owners at least claim to be happy with their pricey acquisitions, some Prius buyers are troubled by nagging indications that Toyota's gas mileage claims for the hybrid may have a little fiction mixed in with all of the facts.

Toyota, of course, insists that all of its mileage claims are based upon standardized Environmental Protection Agency (EPA) tests.

But for Sandra C. of Bloomington, Indiana, the figures just don't add up. In fact, she says she was told the onboard computer in her car is programmed to provide high mileage numbers that may exceed the miles per gallon the car actually achieves.

Sandra bought her new Prius in the spring of 2005. “I've been watching my gas mileage and have consistently gotten around 34 miles per gallon,” she wrote to ConsumerAffairs.com. “That is far below the sticker information and hype.”

The Toyota Prius advertises on its sticker that the EPA has determined through testing that the car achieves an average of 60 mpg in city driving and 51 mpg on the highway.

Sandra took her Prius into the dealer for a check-up and was initially told that she was getting 46 miles to a gallon, which is less than the amount claimed by Toyota for city driving but still a pretty enviable figure. The service technician turned on the gas mileage icon of the onboard computer for her to prove his point.

“The computer did say 46 miles per gallon,” Sandra wrote. “I asked them why it is that when I divide the miles from fill-up to fill-up by the gallons I put in, I get 34 or 33 miles a gallon?”

The service technician admonished Sandra that she probably had her math wrong. “I said no and I wanted an answer,” she said.

Finally the service department manager told Sandra, “Yes, you are right, you probably are getting 34 miles to a gallon.”

When Sandra asked why the computer spit out the higher inaccurate, number the service manager told her, “That is a number Toyota has programmed into the car which accounts for wind resistance and other factors,” she said.

Voodoo Math

Susan did not buy the service manager’s story which she says is nothing more than voodoo math.

“I said to him that is fuzzy math and dishonest. His reply was every car dealer does this,” Sandra said.

Needless to say, Sandra is disappointed and unhappy with Toyota.

“I've been screwed by Toyota. I don't actually blame my local dealership because this isn't their problem. Toyota has pulled this over on the public to sell their car. This must be happening to everyone else too.”

Sandra’s mileage problems with her new Prius continue.

“I filled it up after using half of my last tank of gas on the interstate and half in town. This time I got 47 mpg. So this looks like I am getting better mileage on highway than in city! That is the opposite of what Toyota advertises.”

Other Complaints

Sandra is far from alone. Prius owners around the country are questioning the Toyota/EPA mileage claims.

• Winternet.com displays the site owner's Prius fuel consumption records dating back to 2002. The lifetime average as of Nov. 20, 2005 is 43.2 mpg, a bit worse than Sandra's experience.

• On another site, randyrathbun.org, a person we'll assume is Randy Rathbun displays his log dating back to March 31, 2002. His lifetime average: 47.332 mpg.

• On the Seattle Electric Vehicle Association Website, a consumer identified as RJF has posted his Prius log, starting July 14, 2005. His lifetime average to date: 49.221 mpg.

This comes as no surprise to automotive experts. Data from Consumer Reports indicates that hybrid cars get less than 60 percent of EPA estimates while navigating city streets. In Consumer Reports' real-world driving test, the Civic Hybrid averaged 26 mpg in the city, while the Toyota Prius averaged 35 mpg, much less than their respective EPA estimates of 47 and 60 mpg. Hybrid cars performed much closer to EPA estimates in Consumer Reports'

Consumer Reports' senior auto test engineer Gabriel Shenhar says that while the EPA test is a lab simulation, Consumer Reports puts the cars on the streets and measures the fuel consumed to more accurately reflect gas mileage.

Denials All Around

But back to the other half of Sandra's complaint. Does the Prius onboard Computer fudge the mileage numbers?

Asked if the Prius onboard computer is programmed to take anything into account when calculating mileage other than distance traveled and gallons consumed, a spokesman for Toyota said, “I have never head of anything like that.”

Toyota environmental engineer Dave Hermance says the EPA city test for the Prius includes 19 stops of at least a few seconds, which take up a "non-trivial" amount of the test and could cause hybrid cars to rate even higher than conventional cars because of their reliance on electric motors, which provide the biggest mileage boost in stop-and-go driving.

Hermance says customers who drive less than seven miles per trip will get fewer miles per gallon, as will drivers who speed. There's a huge range of customer behavior and limited resources to collect data, so there's no perfect test, according to Hermance.

As it turns out, drivers of all kinds of vehicles don’t often achieve the mileage EPA finds in its tests. Most drivers get between 75 to 87 percent of the EPA rated estimates with variations based on driving habits and traffic.

A generally accepted rule of thumb is that if a new car gets less than 75 percent of its EPA rating, then there is something amiss. Sandra’s Prius is just at the limit of the 75 percent rule.

“If this is true, then the EPA needs to change the way they do business for hybrids and Toyota knows the figures are incorrect and are creating false advertising,” Sandra said.

Indeed, Sandra is not alone in her assertions. Some independent test data suggests hybrid cars routinely get less than 60 percent of EPA estimates while navigating city streets.

The Prius has averaged only 35 mpg in some city driving tests, inidcating that there may be nothing out of the ordinary with Sandra’s Prius, suggesting instead that the EPA numbers and Toyota mileage claims based on them are in error.

About That Computer

While the test data can explain the actual mileage Sandra was able to obtain, the Toyota information does nothing to explain why the onboard computer in her Prius provided inaccurate information at her dealership.

Toyota spokesman Sam Butto flatly denies that his company programs any “fuzzy math” into the Prius onboard computer.

“I can tell you that Toyota does nothing to have a preset fuel economy figure and does not take into any account the wind. The meter simply calculates the fuel level and the distance driven,” Butto told ConsumerAffairs.com.

He once again pointed a finger at the car owner stating that “it would be extremely difficult to have fuel economy figures that low on a Prius."

"I'm not saying it is impossible. Extremely aggressive driving habits can definitely contribute to lower fuel economy but 34 mpg would be really tough to achieve on Prius," he said.

Butto had another scenario for the low gasoline mileage. “What we think may have occurred, is the customer could have possibly reset the fuel monitor before refilling.”

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