mpg calculated vs computer

I have heard from Cleanmpg.com , Wayne Gerdes, that the computer is more accurate this time around than the 2010/11 Prius. That this was told to him by Toyota engineers.

I believe it was off by about 1.5 mpg when Gerdes checked it which is a lot better than mine which is consistently off 3-4 mpg.

If you have the new Priuv V just fill it up to the top of the neck where you can see the standing gas. Drive for x amount of miles and than refill to the top of the neck again and check your calculated with the computer for verification. Real easy to do, than post your results; it will be appreciated.

alfon

Doesn't this go against warnings not to top off your gas tank? Aren't there mechanisms that can be damaged by overfilling?

That is what Wayne Gerdes did when tested the Prius V.

I have filled ours that way once and a while, and no lights, bells, or whistles went off. The tank will hold and extra 2 gallons of gas when filled that way after the first click of the gas pump.

There is also nothing in the owners manual, at least in the 2010, that states not to fill the gas tank to maximum. If there is It was not printed in mine.

al

My Accord manual says - 'Do not top off the tank. This leaves room in the tank for fuel to expand due to varying temperatures.'

I would think that's true for all cars, especially with warnings posted at the fuel stations.

mpg displayed 47.2
mpg calculated 47.4 this is for the first tank refill. I only went by the nozzle clicking off, not filling up to the neck of the tank.

Any additional stats on computer vs calculated mpg...

al

With just a couple of fill ups I think any variations in pump shut-off will cancel out. I've never been a fan of filling to the neck, for various negative reasons, not the least of which being it takes too dang long, tends to tick off anyone waiting behind you.

Also, Toyota says they are making the computer more "accurate"? IMHO, that's a polite way to put it: why is the inaccuracy consistantly, with every Prius owner, in their favour, by 6~8%?

It looks impressive for people who don't actually calculate their real MPG.

My last tank, computer indicated 60.2 mpg, calculated is 56.3 mpg. 2010 model III, 45,600 miles.

It appears that the 2012 Prius V has a more accurate mpg gauge than
the 2010-2011 Prius models.

Now, I just wonder if the 2012 Prius willl have the same software for
their mpg computer gauge. Also, the new and improved 2012 Camry
Hybrid, these are issues where we should have positive answers
shortly.

alfon

After 2300 miles, approx.700 miles on interstate averaging about 65 to 70 mph, the remaining miles in town or 55 mph traveling. Calculated MPG is 45.3. Displayed MPG is 46.6. So displayed is + 1.2 MPG.

thanks for the info. Our Prius, is off on average about 3.5 mpg optimistic.

Toyota should apply proper software to make all the 2012 Prius, and
other models more accurate in the mpg gauge. In fact even the 2010-11 model Prius, now that they know the mpg gauge was inaccurate.

Most people don't bother to calculate mpg's and rely on the guage.

alfon

I agree with cycledrum. I distinctly remember reading in the owners' manual to NOT top up. There is a flexible bladder in the fuel tank which is supposed to help control fuel fumes. If you top up, you stretch the bladder, causing it to lose its
function.

I stop filling the gas tank when the nozzle switches off. My manual calcs differ from computer shown display of mpg by as much as 3-4 mpg, and then sometimes there's hardly any difference at all. I have no idea why.

Your numbers work out to 2.8% error. That's a fair bit less the regular Prius owners are finding. Our error is at 6.4% right now. On the optomistic side, of course.

This is a v forum.

Yup. The EVAP system, specifically the charcoal canister, is not designed to be filled with liquid gasoline. Overfilling can kill it, throw error codes, and eventually end up in an expensive repair which may not be covered by warranty.

Just fill til the nozzle clicks off the first time (slowing down as you approach full to avoid premature click-offs). That plus making sure the car is level when you fill will be accurate enough.

If you want even greater consistency you can fill at the same station and use the same pump (not always possible, obviously).

At 4930 miles, My displayed mpg reads 48.0. The calculated mpg is 45.3. It has been running at this 2.6 / 2.7 mpg difference for the last approx. 2700 miles. This is in FL. weather and flat terain for approx. the last 3000 miles.

I have had about 10 fill-ups since getting my Prius v. My driving has not changed during that time. The car's computer estimates I'm averaging about 43 MPG. My own calculations with each fill-up shows that I'm getting about 41 MPG.

41.9 for the computer, 38.9 for the fuelly.com calculation. This was only our first fill up in the car though so I expect it will get better