Actual Gas Millage vs Estimated Millage

Yeah, there are lots of posts about that, the computer is optimistic on the Prius, mine is averageing about 2.5 mpg too high and that seems about the average. You can do a search of the website and find a lot of posts, most of them are close to what I found.

 

Ditto. Mine is also about 2ish less when I calc it manually.

 

I think Toyota done this intentionally with the optimistic reading. I wonder if other types of vehicles read the same way?
I only know 3 people with MPG read outs on their cars and they don't manually calculate. I asked one of them that has a mini cooper to manually calculate next time because I was curious if it would show an optimistic reading as well, and he got all defensive and said he didn't care and he was happy his dash read thirty something MPG....ah okay whatever, thanks.

My error range is from 4.5-8.5% optimistic, averaging 6-7% optimistic. Your first tank is a pretty wide margin @ 12% (11.99% to be exact).There is a sticky on "Gen III 2010+ Prius Fuel Economy" room with calculated vs computer MPG results if you are interested.

 

My average discrepancy is 8%, with over 2 years calculated now. I too think it's Toyota looking for some cheap promotion. It's sad, considering they have such a fuel efficient vehicle, to muddy the waters with this nonsense.

 

Finally, never calculate your first tank if the dealer "filled" it.

 

See calculated vs. computer MPG - Please post your results | PriusChat

 

I've manually calculated mpg on mine with every fill up and it's always been off by at least several mpg's. Last one I was so happy to have achieved 65 mpg but then i calculated it myself and it was 60...LAME. My overall mpg after 30k miles is approximately 51 mpg, and based on my calculations, i'm actually getting closer to about 47 or 48...kind of a bummer. I definitely feel that toto mislead all of us with their mpg figures of 50 combined. oh well...once again, the consumer just has to eat it.

 

It depends on the car. Gen 2 Prius' MFD is pretty accurate if you compare its readings averaged out vs. manual calculations averaged out.

My former 02 Maxima's trip computer was usually 2-4 mpg off which is a pretty big amount for a car that typically gets in the low to mid 20s for mpg given a fair amount of highway driving. My former 04 350Z's trip computer was more accurate: within 0 to 1 mpg off, usually within 0.5 mpg or so, IIRC.

 

I have been keeping a spread sheet for two years and more than 28,000 miles. A 4 - 6% differential is common. Only once has my calculated mileage been higher than my indicated mileage. Through it all, I have averaged an actual 51.382 MPG.

 

When I had the Cadillacs, the gas mileage readouts were usually within 10ths of the pencil & paper calculations. With the TDIs, the readouts were optimistic, reading 4-5 mpgs over the P&P calculations, until the '09. On that car, the readouts were within 10ths either way. The '11 Prius readout was about 2-3 mpg over P&P. The PIP is running 4-5 mpg over.

 

My actual is about 2mpg less as well.

 

In my '10, my GPS indicates the speedometer error is about 1.5 mph. This would contribute to the problem.

 

Dang it, no. There's a leap of logic there, that goes off a cliff, LOL.

The speed display is purposely high, legislated so. A speedometer isn't allowed to show lower than actual, and can err, by a legislated factor, on the high side. The idea being that the car shouldn't ever tell you you're going slower than you are.

But the car knows the actual speed, and distance travelled, behind the scene. The odometer should be reasonably accurate. If it isn't there would be lawsuits, over misrepresented miles travelled.

The mpg indication though, could be made more accurate. The smoking gun is Toyota's possible motives for exaggerating the numbers.

 

Nope. MPG is calculated from the odometer, not speedometer. They have different errors. My Prii odometer errors have been miniscule, no more than 0.2%, and always reading low, the opposite direction of the speedometer error.

As Mendel mentioned, speedometer errors are biased to the high side for legal and industry standard reasons.

But odometers cannot have the same error (at least these days) without rolling out the red carpet for the class action lawyers who already took the makers of two of my previous car brands to the cleaners over alleged 'warranty fraud'. They extracted millions in fees for themselves, and a 2% warranty extension for customers. But neither of my covered cars actually had this alleged problem.

 

I had over 3 years of reading and every tank registered and calculated for my first 2010 prius ... it is about 5% consistently .. so if you are reading in the 50MPG range on the MFD that means you need to deduct about 2.5 MPG if you are around 60MPG then about 3 ... and so on...

I think this is NOW well documented. And I am very disappointed with Toyota my GenII was within reading error (I mean the pump and click methode is not that accurate !!)

 

As others pointed out speed reading is not accurate either !!! But that is by law !!!

Unless you change you tire from the OEM spec the odometer is very accureate even over 100K miles ... the wearing of the tires effects it a little but not really significantly.

The computer intentionally reads high .. with a SG you can get within reading error !!! So the car actually measure those correctly !!!!

 

The read out on my 2006 corvette is always dead on. The read out on my 2004 4runner is 2-3 mpg optimistic. So I guess it's probably most toyotas. Not just the Prius.

 

The Consumption display on my Gen2 Prius was pretty close. The Gen3 is off by about 4% to 5% as all the Gen3 cars seem to be. Toyota's way of making you happy.