Will there ever be a fix for the MPG estimates?

Good question. Perhaps Toyota needs to know that it is a problem first. I suspect we all need to contact them all at once for them to realize there is a problem.

 

I suspect it has something to do with salesmanship. Most drivers (perhaps excluding Prius owners) do not ever calculate the fuel efficiency. I confess, when someone rides in my car and they exclaim what wonderful fuel efficiency. I silently think well in truth, it is 3 mpg less. Perhaps Toyota purposely mis-leads owners .... but my brand new CRV is not dead-on accurate either, and I suspect few vehicles are.

My personal view is that I am deeply grateful, and satisfied, that my Prius is performing so well. I am not too critical of a small error in the display. If I let that disturb me, I would be in constant turmoil from just about every aspect of our society: unfulfilled political promises, biased media reporting, unreliable weather reports, to airline schedule delays. Our society is not perfect .... why should we expect perfection in our vehicles instrumentation? especially if there is some corporate advantage to "fundging" a bit in the positive. I have never heard of a vehicle that underestimates the fuel efficiency.

 

For me it is not a true problem if the error remains constant (e.g. 6% like now). If it changes, then the indication is not at all reliable, and I would require a fix. If it is constantly making the same mistake, it is not accurate, but at least not broken.
Likely for cost reasons they decided not to make it more accurate. I think there are technical challenges to correctly estimate/measure the actual fuel consumption in a car, that only very costly solutions can address - probably it was estimated that a 5% (in fact higher, including pump "mistakes") was acceptable and not so many Priuschat members would measure it so *accurately* as we did...

 

I wonder if it's worse on the latest generation or it varies a lot. I keep detailed records on my 2005 and over the first 74,000 miles the difference between the computer and actual mileage is 2.69%, with the computer being on the optimistic side. It would be nice if the owners could "dial" in their own correction factors, but in my case 2.69% seems close enough.

 

I fully understand the desire for accuracy of data presented by the car. I look at the bar charts for the shape and variance between other bars, not for the absolute value of the bars (quantitative). I suppose that is because I am not a hyper-miler, just an average driver who gets a kick out of this car. In short, I look for changes in their shape (height) relative to one another in order to see trends and general information. I doubt that I will ever calculate what the actual mileage is, rather, I will just scan the bars. I do wish Toyota had made the Y-axis a little more detailed, such as the low value being, say, 30-MPG and the high being 75 or so since this is where the car spends most of its time.


Enjoy the ride!

 

For the Gen III owners that keep careful records it appears to be fairly consitantly close to 5% optimistic when averaged over several tanks. It looks like the 5% optimism is intentional.

 

Well I'm up to 5900 miles, so it just a baby, but my error rate is anywhere from 7.2% to 10.6% differences so far. The average is 8.7%.

Otherwise nothing else is going wrong, so it just looks like a calculation error

I wonder if V's have a higher error rate because of the 17" tires...

 

Bob's numbers are a relatively constant error for real world measurements using what we the general public has available, the average was 8.7% and the variation is +1.7%/-1.5%.

Assuming a fill up is 9 gallons, 1.5% of 9 gallons about 1 pint or about 1/8 gallon. A fair share of that difference could be differences in how the tank was filled and a smaller amount of it pump error. If the MID display were perfectly consistent (I'm not saying it is) you could still get variations like that.

 

how do you know the pump numbers are accurate? is it actually filling 9 gallons? maybe 9.03? 8.97? Isn't the Prius fuel metering very accurate (injector counts and flow thru?) And does it matter when emissions are lower too, but no one complains about the air we need to breathe? sorry, too many questions...

 

I've had the same optimistic numbers from my 2010, but last summer I took it on a trip and found that when you drive continuously at freeway speeds for 600+ miles the computer actually indicated less than the actual mileage.

 

That's a good point -- perhaps the couple of gas stations that I frequent aren't all that accurate in measuring what they pump. I suspected one of them wasn't but not the other. Maybe they don't inspect them as often around here...

 

No doubt there are out of calibration gas pumps and crooked gas station operators, but I think the biggest difference is the consumers ability to consistently fill their tank. That is compounds by differences in when the gas nozzle clicks off and any slight sideways tilt of the vehicle.

Legally required pump accuracy varies by jurisdiction but 1/2 of 1% or less than 1 cup in 10 gallons, or 1/2 of 1/10 gallon is common. It would be difficult to consistently your tank to that level of accuracy given a perfectly accurate pump.

 

The car is OK ,it's the loose nut behind the wheel. I get 10%-25% better than their estimate. Maybe you should drive a little slower and let up just a little once your up to spped. That puts the CVT tranny into super efficient gearing and you do much better. It's all in the driver.

 

Did you read the thread before you responded?

 

you could fill a 5 gallon gas can and visually get a pretty good idea of how accurate the pump is.

 

It's a pity they don't have some kind of visual gauge built in to make it easy to fill the tank to the same spot...

 

On the Gen III you can carefully fill it until the gas level is visible.

That still doesn't correct for any slight tilt of the car which as a PDOMA could easily make a 3+ tenths of a gallon difference.

 

Or out of spec pumps!

I know, it was a bad idea.

I guess nothing short of more hardware and software to measure the exact gas usage. (and thus more cost...)