First tank Fill up

I've been keeping track of every tank. My car now has 5000 miles on it. The calculated mpg for each tank varies widely, due to the problems getting a consistent fill. Just today I entered all data into a spreadsheet and found that for the 5000 miles my calculated MPG was 45.2 and the computer display average was 46.0.

I still don't trust it completely, but it looks like the display is pretty accurate.

Congrats on the new car.

 

OK, a question for experienced Prius owners. I did my first fillup today as well. Had 39.8 mpg on the MFD. (Very satisfied, I drive short trips and used to get 15.5 mpg at best on my Audi and had to use premium).

The fuel guage went to full by the time I left the station. The miles in the MFD reset to 0 in 100 to 200 yards. All as expected.

However, I had an ideal drive home of 7 miles on back roads. In the 7 miles home, the MFD gave me only two 5 minute segments, both showing 50+ mpg. By the time the second one popped up, the MFD indicated the tank average was only 39.9 mpg at 5 miles. The rest of the trip home was downhill and at home with 7 miles, the MFD indicated only 40.1 mpg.

So how long does it take the MPG indicator to reset? I would have expected 50 to 55 mpg by the time I was home. As it is, it seems to be still averaging into the 39.8 mpg I had at 360+ miles. I'd expect somewat of a slow reset so the numbers don't jump around too abruptly, but not this slow.

Barb's no help with her 2005 Prius - she never pays close attention to the indicators after fillups.

- Tom

 

The thing you have to be aware of is that mileage DOES NOT average over time. If you average 100 mpg the first 5 minutes and 30 mpg the next 5 minutes it's mathematically impossible to say what your average mileage is going to be. So the Consumption screen bar graphs showing mileage for every 5 minute segment are really useless to gauging how well you are driving. You really really need to view the Energy screen, look at the instantaneous mileage and what you gas engine, electric engine and battery are doing.

Read the following that tries to give better insight of how the mathematics of average mileage really works.

http://priuschat.com/index.php?showtopic=1...03&#entry180703

After 2000 miles of driving I've gone from a 40 mpg tank driver to a 50 mpg tank driver. The only quick rule of thumbs are try to do your best to avoid ever having single digit mpg's on your display. If you can succeed in doing this than you will have trained your foot to be very light and you will be well on your way to approaching 50 mpg. If you are unable to avoid single digits except for a couple seconds than you'll probably hit squarely in the 40's. The other key thing is you need to learn how to feather the accelerator and coast with either moderate electric only power or no power. Do whatever you can do to keep your momentum up and have the mileage show up with 90 mpg or higher You need to get into the "zone" and the "zone" is when you see 99.9 mpg for extended periods of time.

 

Based upon what I've seen and read the computer display is probably more accurate than your calculated value. The true gas mileage if you could reliably fill up the tank consistantly would be a lot closer to 51.73 mpg than 54.44 mpg. So while you might be slightly euphoric to see higher than the computer display, don't get too excited because it's going to balance out with a lower than computer display.

Basically, just trust your computer display. From what I've read the computer display has been performing within about 2% accuracy.

 

No freaking, I'm an engineer and that is what I'd expect the indicator to do. I'm asking because it is -not- doing that.

This morning I did my usual commute in 34' F temperatures. The mileage stayed rock steady at 40.1. It now has 16 miles on that tank. In Barb's '05, the mpg plummets during the warmup then climbs back up as you drive when she only has a few miles after fillup. My '06 did the same thing when it only had a few miles on it. It really looks like the fuel guage and tank miles on the MFD reset, but the mpg indicator did not reset. It is averaging the current driving over the miles of both the last tank and the new tank of gas. New behavior in the '06 or a glitch?

I should have had a real high mpg after filling up and driving home for 7 miles with all segments showing 50 mpg+. It didn't - it drifted up by a couple of 10'ths.

It will be interesting to see what it does on the next tank.

- Tom

 

Nice spreadsheet Steve! I wish more people would keep track online. Put the Miles Driven column in there too and shoot for the elusive 600+ Mile tank.

Here's mine... http://www.w8kc.com/priusmileage.htm

Hmmm... I should probably give it it's own site and get rid of the slash in the URL...... good idea!

 

http://prius.w8kc.com

cool... I love this stuff.

 

It look like this is a bug or "feature" in the '06 like the AM radio voice command wierdness. I just talked to another engineer here at work that got his car the same day as mine. He has 1200 miles on his and 4 tanks of gas. He noticed the same thing - the mpg indicator in the MFD was acting like a lifetime mileage indicator. With about 1000 miles on it, it essentially stopped changing even with widely varing driving conditions.

On the last tank he hit the reset button and the average mpg indicator went back to normal - changing a lot for the start of the tank and less so after a couple hundred miles.

Both of our cars are 11/05 build dates. It looks like you have to use the reset button to get it to act like the earlier cars. Nothing about this in the manual.

- Tom

 

Yeah, looks like I'm a prime candidate for '05 vs. '06 comparisons. I bought Barbara a 2005 last Febuary for her birthday and got my 2006 this January. I only get to drive the '05 on Sunday mornings to get the newspaper - 1 mile inside a subdivision. I'll have to pay more attention now.

- Tom

 

This seems to be as good a place as any to post, as I too, just took my first trip to the gas station.

1. The MFD consumption screen didn't zero out my mileage as I expected when I turned the car on. I did hit the "reset" button to accomplish this, but I am curious if it would have zeroed out by itself, or does it update on 5 minute intervals, or what?

2. Having driven 406 miles from the dealer's initial fill-up, I was surprised the pump shut off automatically at 5.599 gallons. (My MFD said I had 48.2 MPG, which I was pretty happy about... I sincerely doubt I got anything like 72.5....) How do other Prius owners fill up their cars "consistently"? I was planning to slow the pump down after it got over 6 gallons, but it shut off even earlier than that...

3. I saw on someone's nifty mileage spreadsheet an "average temperature" column. I suppose they could have used some data from the web to calculate average temperature in their city, but then it occurred to me that somewhere in the car's software it has that information (the outside temperature for every minute it's on)... Don't suppose there is any way to get at that data...but I thought I'd ask