2010 Toyota Prius FCD Inaccuracy

miles... MFD mpg.... MFD gals... pump gals... pump MPG
268... 57.8... 4.64... 4.400... 60.91
614.5... 62... 9.91... 10.339... 59.44
448.5... 63.6... 7.05.. 8.335... 53.81
622.9... 68.1... 9.15... 9.983... 62.4
569.8... 60.7... 9.39... 9.940... 57.32
516.3... 61.5... 8.4... 9.661 ...53.44
632.7... 64.1... 9.87... 10.893... 58.08


ok...cut and paste not working EXTREMELY well. hopefully i can make look ok

MFD gals and pump MPG are calculated based on numbers provided by MFD MPG and gas sales receipt respectively. i manually reset trip A on every fillup which is where the miles reading and MFD MPG are taken...

as far as numbers go, Wayne plus a few others have mentioned that higher numbers have greater errors not only in raw numbers but higher percentages as well

 

Based upon 80 samples collected at PriusChat, it appears the following correction gives a first order conversion from indicated to actual MPG:

• actual_MPG ~= (.84 * indicated_MPG) + 5.66 :: between 45.0-61.0 MPG

The below unity slope, ~.84, means the error grows for larger indicated MPG values. However, we do not have enough data points above 61.0 MPG to be sure the relationship hold true for larger values. The outliers are too sparse.

If you have additional samples to add to the pool, please post them to the sticky thread. Once we get at least 10% more (aka., 8 or more,) I'll add them to the sample set and we'll get an even more accurate understanding of the relationship.

One area we especially need are more data points above 61 MPG. I'm tossing out the upper 5% and lower 5% to avoid having outliers over-ride the 90% of data points of interest. There is not enough information to tell what is going on above 61 MPG indicated.

The best way to understand the higher, indicated mileage numbers is to generate them. For example, if someone can run their 2010 Prius at say 20 or 25 mph for at least two gallons, this would help a lot.

Thanks,
Bob Wilson

 

I hope this isn't true of all Priuses because my new 2010 Prius only gets about 43mpg. I'd hate to think I might really be getting less than 40 mpg.

By the way, I'm not an aggressive driver. Maybe I don't know the tricks for getting the best gas mileage, but I was still expecting a better number than in the low 40's.

I'm on my second tank of gas. Hoping for improvement. Any advice from other Prius owners?

 

Here are a few ideas you might try:

Use high tire pressures, with your car maybe 42/40 lbs
Read everything pertinent in the fuel economy forum
Learn to drive by using the HSI and stay out of the power zone
Plan ahead, try not to use the brakes any more than you have to
When you do use brakes try to use regen braking without getting into the friction brakes
Drive the car in the ECO mode only.

 

[snipped]

 

A learning curve is natural when getting used to the Prius. In no way was this meant to be derogetory by any means. The Prius is a wonderful car that can produce very good results but does have a learning curve.

You have to adjust the way you hit the gas or you end up in the PWR side more times than not and this tends to cut in to your mileage results. The car is very sensitive to that, and once you can observe your actions more and more and tune them better you should see an improvement for sure. I have had my car only one week...and was able to achieve on the MFD 59.9 MPG yesterday for 45 miles of driving. Even with the potential error ratios that some of the posts are indicating, I would think if the number was closer to 55 (giving a big adjustment) that would be great numbers. But I must admit you have to be easy on the gas as I say. Today driving those same miles, being more agressive and not being as careful, yielded a different result over the same route, with same weather conditions. Today's result was 47.9 MPG, and I used Power Mode 2x's and was not gentle on the gas. So as you can see the numbers change rather easily. All the comments about maintaining speed, watching braking, pulse and go techniques all are great commentary and do work.

I think the more you get used to it and learn the balance, the better your mileage will get.

Keep us posted on your progress....Good Luck.

 

The battery charge at beginning and end of the measurement period also need to be taken into account. That means it's best to average over as long a run as possible and you have to be careful in factoring this out. I can get great mileage for some runs, but it is usually when the battery charge starts high and ends low. I wonder how many of the posted results factor this out?

 

I may be wrong here, and if so forgive me; but I believe that the newer manufactured Prius's have more accurate MPG guages than the earlier ones like mine. I purchased mine in May 2009, and its vin number is in the 2,000 range.

Mine has been always off by 2-3 MPG, consistently for over 8,000 miles. The last fillup it was even off more with indicated 51.1 MPG and calculated 47 MPG.

This can easily be corrected by Toyota and it probably already is being done as you read this.

alfon

 

I have a July build date VIN over 30K. I'm still collecting data but so far it looks like I will be just as far off as everyone else. I see 4 to 5 MPG errors in the 50 MPG range.

 

I agree with sbeach. We did not buy a Prius to become hypermilers. We have been getting about 52 MPG on highway trips, OK. The wife drives 4 miles to work and the city milage has dropped to 42. I have read the threads talking about engine warm up and reduced mileage. We also switched brands of gas on the last fill up. It was the first time the gauge went below 2 pips and that last pip only lasted 14 miles! I stopped at a Sheetz for gas.
We normally use Sunoco and I have found the Sienna gets 1 to 2 MPG better citi mileage with Sunoco gas. The Sienna gets 17-18 city. The same percentage difference would be 3-6 MPG in the Prius! Is anyone else seeing this kind of difference with the brand of gas you use?
Bob

 

Yes!

I found the brand of gasoline does make a difference as my last formal tests showed in the Huntsville AL area:

• Shell, Exxon and Chevron - were about 5% better than
• BP, Citgo, and Texaco - poorer performance
• E87 - performed about 5% better than
• E89, E91 - same brands

I believe your fuel comes from the east coast and/or possibly some from Canada. Our fuel comes from the Gulf coast. I'm pretty sure there are regional differences so it pays for folks to try different brands to see the relative performance.

BTW, your mileage is consistent with what I'm seeing with our ZVW30. It takes about 5 miles to reach 50 MPG due to the engine warm-up time. A block heater and/or lower radiator block may improve your wife's short distance performance ... but +40 MPG is something many folks would admire. Another approach is to see if your wife can spend more time in 25 mph, neighborhood speeds on the way to work. This can reduce the warm-up fuel burn enough to have an impact.

GOOD LUCK!
Bob Wilson

 

Not only are there regional differences in gasoline, but regional differences are often mandated by law. The United States is a patchwork of fuel regulations.

Tom

 

what brand is Costco?? hmm, interesting question. i am sure they probably do bulk buy from one company. next time i gas up, i will check on that. will be a week or so.

 

So lets say Toyota fixes any aberrations in the software... just how will we be made aware and get the update?

 

I've seen various unmarked tankers filling the storage tanks at my local Costco.

 

Seems the type of Gasoline could and "should" make a difference when you consider all the choices, types and prices of those different types.
The prius doesn't necessarily do better on the expensive high octane stuff, but my point is that there are differences and unless we are all using the same gas in our comparisons, its hard to compare.

 

I believe that the reason of observing different MPG result using different brand of gasoline is caused by different energy contents of the gasoline.
We see the lower energy gasoline causes the worse MPG result.
But, I believe the ratio between indicated and calculated values does not change on that situation. We see the worse MPG results on both indicated and calculated number.

I also believe the Toyota engineer's comment, intentionally biased MPG display, is true.
It is not a technical issue, but it is Toyota's marketing policy, I think.

Ken@Japan

 

I'm afraid you're right. Disappointing.

 

I just finished a quick 6 day highway trip:

3353.1 miles, 49.7 MPG, Avg Speed 59 MPH as computed by the car

Using the same odometer miles and gallons of fuel used from the gas pumps I calculate 47.58 MPG.