calculated vs. computer MPG - Please post your results

"Have you ever had an entire tank below 40 MPG?"
Wow, lowest I ever got at any time of the year was 42.6 for a full tank. This is before I started hypermiling and driving aggressively in power mode.
I guess I shouldn't complain about my mpg's in the summer.

 

This will be my first winter with a Prius and with temps in the 40's and 50's I can already see a difference in FE. I can't imagine what someone might get during the winter if they own a Prius in northern climates, don't own a garage, and have a short early morning commute. Maybe 30-35 mpg?

 

You get excellent MPG. I'm curious to see your average in the winter.

 

Thanks, I'm curious to see as well. I still think I can keep the average above 60 for these reasons:
1. I'm taking a road trip down to Orlando for almost two weeks of winter.
2. I have a garage that stays above freezing even in the coldest temps.
3. Whenever we have bad snow or ice I will be driving my 4wd truck.
4. Whenever temps get to single digits or below I will drive my truck.
5. I am going to be fairly aggressive with grill blocking.

 

There are a few similar reasons that will have the opposite effect on my FE

Me, too! But I'll be driving something other than my Prius, which will be parked in the freezing cold, back home.

I have a garage, too, but in mine I don't have to plug the freezer in during the winter.

You'll see me tooling around in my Prius. I now have some better-performing all season tires that will help keep my FE down even more!

. . . and I'll be in my Prius -- with the heated seats giving their all to try to keep me from becoming a human popsicle.

I may be going back to grill blocking. I did it for my Gen II (and wrote an extensive post on it, too!), but I thought I'd try the Gen III without grill blocking. Three winters may have been enough of an experiment that way.

 

OK. I have been keeping a gas log on my 2008 Gen II Touring since I bought it. Up until a few months ago, the error between the dash MPG and the "actual" mpg has been around 1%. Since then, it seems as though it's now in the 4%-5% range. I can think of three possibilities: the gas pump was changed to read optimistic, I'm losing gas somewhere, or the dash mpg has lost calibration (injectors now letting in more than before?).

Has anybody else seen this, or am I the umpteenth person to post on something like this?

 

I have a wide difference on a 2012 Prius.
The door tag says 12/11 - I guess that's Dec. 2011 manufacture?
Over the last 5 months I have driven 9688 km in fall/winter urban conditions. No grill blocking, underground parking overnight.

Dashboard claims 5.1 L/100 km (46 mpg)
Calculations show 5.50 L/100 km (42.8 mpg)
Which is a 7% error in the fuel flowmeter.

 

This is all difficult to verify.

I find the MPG Average on the Trip Computer (A or B) to be 2 to 3 MPG more than manually calculated.

The only way to get reasonably reliable data on this would be to fill a scientific measuring device to a gallon and fill your tank to the absolute top based on reliable measurement information. My manual states that my tank capacity is 11.9 gallons. (I assume this is to the top of the filler neck.) And some engineers could probably go on extensively about the amount of energy in fuel based on the season, octane rating and lack of reliability and oversight of said octane ratings. Lots of variables here including circumference of tires as they wear down.

I can say with certainty that the 2010 Prius I own gets REALLY good MPG compared to any other vehicle I have owned by approximately 15 to 20 MPG's. The best I got with my VW Golf 1.8T was around 31 MPG. My Prius always gets above 45 MPG. Of course, before I got the Prius, I did not have time to work out the math as I was too busy trying to fix Windows falling into doors and other nonsense that have caused German cars to be at the bottom of the reliability ratings...

 

This is a little high, but within the spectrum of "normal" for the difference between hand calculated vs computer displayed. My lifetime displayed vs calculated difference is 5.7% (it increases in the winter time and decreases in summer).

 

Although the tank is rated as 11.9 gallons, the tanks can vary in size (it isn't a hard rule). Many people can squeeze in another 1 - 2 gallons by filling to the next (getting 13+ gallons into the car). The simplest way is to track your mileage and your fuel consumption over a long period of time. The minor deviations will even themselves out over time. As the mileage and gallonage values increase in size, the variations from fill-up to fill-up decrease in magnitude.

 

Hi
I have only had my 2010 model Gen III T4 for 6 weeks, I did have a Gen II for a year in 2009 though. I am using Fuelly and brimming my tank at every fill-up. So far, actual mpg (UK) is 51, whereas my trip computer is showing around 54-55mpg. As it has been cold here for the past month I am pretty happy with that.

 

We have had our 2012 Prius II about 6 weeks and the best mileage we have gotten is 44 mpg. My wife is ready to give it back to the dealer. Very frustrating. I think we are going to take it back to the dealer to have it checked. It was manufactured in July 2012 from what I can tell on the door tag. The one thing I do notice about the car is a whining noise when she's pulling it into the garage. Sounds like some sort of SciFi noise.

 

But 42.6 is not 48 -51. Which is the claim.

 

Hello

Welcome to Priuschat.

The Sci Fi noise is the vehicle proximity notification system (VPNS).
Not sure where you are located, but in cold temps normal driving (not hypermilimg) could get you average mpgs in the mid 40s.
The car might be fine.

Btw - you may want to change your vehicle year to 2012.

Edit, wanted to add - there is a post for complaints about getting low gas mileage, you can answer the questions and get feedback from other members.
Fuel economy complaints/queries? Please copy, paste & answer these questions, esp. if you're new | PriusChat

 

After reading some of the stats, I decided to put together a quick spreadsheet from my fuelly results. For approximately 22K miles I averaged 53.6 real mpg and 56.8 displayed mpg for a difference of 5.97%.

My method for fueling is to go to the first click and then add fuel to the next dollar. The difference in fuel added to the next dollar will average out over time.

 

As someone who has been driving in cold temperatures since I bought it let me say this.
Temps make a huge difference on mileage especially when you are new to driving it.
Also keep in mind all cars drop in Winter time.
I only had 1 tank on my car before we had snow, and I had snow tires on my car. I have averaged 44.6 so far since I have owned it, bought in middle of October.
When the weather is a little warmer in the afternoons when I go home, I can get over 50-54 no problem, some mornings I can get over 50 too but when it's below 40 and takes longer to warm up my mileage drops down to like mid to lower 40's.
I do not warm up my car before hand, I do scrape all my windows before I start it, and do my best to coast while my car is warming up to maximize, I have a short hill both ways on my commute right after I leave.
When running errands around town or on short trips when my car is still warm, picking up the kids from daycare etc. I can average right around 60-74 mpg pretty easily.
It's nice to drive completely across town from one end to the other and have it cost you $.09, I don't think anyone else on my street can go 2 blocks for that price.
I would say give it time, you will not have an easy time returning your car at this point, and as soon as the weather warms up you will see an improvement.
I have watched my average go up and up as I got better at driving my car.
Oh and I do have my lower grill totally blocked which I know helps with my warm up times, best $4 spent ever.
I think I could switch to my OEM tires and keep it above 50mpg every time already but it could still snow again so I will wait another week or 2, and when it warms back up here in the NW I expect to be over 60 on my commute hopefully.
My longest trip in the Prius was in Nov.. probably 35 degrees out, only a 300 mile trip, but averaged over 60mpg there and back.

 

Check tire pressure? Try 35 psi or a little more all around. Made a big difference with mine. Do you drive easy up and easy down - acceleration and slowing?

 

I wonder if the whining noise you describe might be the voltage inverter in the engine bay. All hybrids or electric cars make some variation of a whining "sci-fi" sound under either acceleration or regenerative braking, or while charging the hybrid battery while the engine is idling. I have a 2008 which has no proximity notification device, so I'm unfamiliar with what that sounds like-- I'm just making another guess.

One other thing I'd point out is with regard to the mileage you're seeing. The mileage in a Prius does drop in colder weather, and the MPG number it drops by at times may look really extreme, but in terms of actual fuel consumption, the difference is actually really tiny.

If I get 60 MPG for an entire tank, I can deliver pizza in my car all week on one tank of gas, and fill up for about $29 (at $3.50/U.S. gal.). If my mileage drops to 45 MPG in the winter, I may have to fill up at 4 days rather than 5-7 (depending on what I do on my days off), but I'm still only pumping a bit under $39 of gas for the week at that point. Considering that I drive around 100 miles per day, that's not a huge difference despite being a drop of 15 MPG.

On the other hand, if you're used to driving a car that gets 23 MPG like my old car, and it drops to 20 MPG in colder weather like it did, then it means I'm spending $76 a week in warm weather, and closer to $88 in the winter. In both cases, it's a difference of right around $10 per week in lost fuel economy, but the numerical loss in MPG in the Prius is FIVE TIMES GREATER than the MPG loss in my old car-- 3 MPG vs. 15 MPG.

So the short lesson is, don't fret over a half dozen or even a dozen MPG variation in a Prius (unless it's an uncharacteristic change, like losing 10-15 MPG under the same driving/weather conditions with the same tires etc.), because in real, tangible terms at the gas pump or out of your wallet, the dollars/gallons variation is MUCH smaller than even a smaller MPG variation in any other vehicle would be even though the difference in MPG numbers themselves are much larger. I hope that makes sense to you.

 

I filled up yesterday-second time putting gas in my 2013 model 5. Trip computer said my mileage was 45.5.
Calculated mileage was 43.125.

 

51,265 miles. 110 tank fills, 971.520 gallons = 52.767 actual mileage. My car MPG computer averages 5% over the actual mileage. So whereas actual mileage has been 52.7 the MPG estimate is 55.5