Gas mileage - HELP!!! 38.3 MPG, what's wrong?

You should calculate gas mileage by starting with a full tank, driving the car, then refilling the tank.

Divide Miles traveled/gallons used = mpg

The way you are doing it isn't much more accurate than using your horoscope.

When miles to empty = 0, you should have very roughly 1.5 gallons left in your tank, but don't count on that.

Your zero miles fill-up will be more like 10.4 gallons than 11.9, so using your horoscope method, you are running about 46 mpg. Not bad for a new car and your driving scenario.

You won't really know how good it is until you fill it.

 

I agree with xs650 that your methodology for estimating your mpg is suspect. What does your display say? Based on the fillups I've done over the past year, I find that mine tends to overstate the mpg between 2-3mpg.

You're on your first tank and the car is still in the break in phase so your mileage should improve over time and there's a learning curve to driving the car efficiently. You can search here and find all sorts of driving tips (pulse & glide) that can help you increase your mpg. If you've been using the A/C that has an impact on mpg.

Enjoy your new Prius!

 

What's your trip meter saying? That will be a better current guide. Subtract 5% for pessimism.

I've hit 0 miles to go by the car's estimate and never put more than 9.8 gallons in. It doesn't even get close to the full tank size.

 

It's too early to panic, mostly for several reasons:

1) The fuel gauge in your Prius isn't accurate enough to give a meaningful estimate of the remaining fuel, other than to say that you need to buy more fuel.

2) This is the first tank: you have no way of knowing how much fuel was really in the tank to start with.

3) Give the car some time to break in before you worry about mileage.

4) Your mileage will improve as you learn to drive it.

Tom

 

That is probably about right for someone like me who was coming from a muscle car and had no idea how to feather the accelerator and how to "pulse and glide". It will come to you. I really think the most important thing for fuel economy is the gauges that show you the effect of various inputs to the engine like pedal depth and coasting.

You will get better, but I doubt that I will ever get to some of the really high mpg results I have read on here. Maybe they are even true.

 

The first question to ask would be, have you read the manual on how to drive a Prius (coasting, braking, accelerating). If you drive the Prius like a normal car, I'd say you'd get around 450miles.

However, if you drive your car like a Prius, you can easily get over 600miles and sometimes even 700miles.

 

The dealer tank is basically junk for mpg calcs so do not worry about it. As others have said the Prius displayed mpg is about 2mpg optimistic but it is close so that gauge is a good indicator. Once you fill yourself then if you are interested you can start manually calculating fuel mileage and a fillup will only get about 10 gallons max into the tank if you are down to one bar or less on the fuel gauge. Also I suggest searching You Tube for the Prius fuel economy video a Prius owner did as it is a great guide to learn max mpg techniques - it will help immensely and you can decide how aggressively you want to apply those techniques. Getting EPA numbers or close is actually very doable once you learn a few of the tips that help max out mpg and you won't be holding up anyone.

Also your car will improve somewhat after 1000 miles or so with break in

 

Hi Lonewolf!

OK, as others have said, it is a bit early to be concerned. If you would like to get a better idea of what you car is doing MPG wise you have options.

The "optimistic" option is to look at the instant MPG read out (for tank consumption). I suspect it is in the 50 mpg range.

The second "less optimistic" way is to take your current mileage on the tank (368) add the miles to zero (96) and divide by 10. This puts you in the 46 MPG area. Likely when you fill up, your mileage will be between these two ranges (and closer to 46 rather than 50).

Your MPG's will improve as the car "breaks in". You are assuming you had a full tank when you got it. Don't sweat the first fill up. You'll have a much better idea of your MPG and range with the second fill up.

Don't sweat the blinking last pip too much either. It usually comes on when you have ~ 2 gallons of gas left in the tank. When mine came on the other day, my miles to zero was around 38 miles. When I filled up (within 10 miles of the pip blinking) I put in 9.7 gallons of gas (thus I had ~2.2 - 2.3 gallons left in the tank). I'm not saying ignore the flashing pip, but rather, don't panic if/when it comes on. You'll likely be able to drive 90+ miles before running out of gas.

 

Lonewolf, I like you a lot, I like everyone until they prove otherwise.* Spend the first two tanks learning the controls, judging your visibility, and breaking in the engine so that both you and the car will last a long time, then on the third tank, you can start practicing techniques for good gas mileage. Knowing how to get into B to go down long hills, and how the brakes feel when you hit a slippery patch are much more important than saving a dollar on the first two tanks of gas. If you have bad mileage on the third tank, everyone will want to help as it is not just the dealer 'short sheeting' you.

*It is sad some prove otherwise SO quickly.

 

I found the first 'dealer' tank was 89 octane, not the 87 that tends to have higher energy content. I was able to detect the difference in hill-climb tests. After driving the tank to 'empty', the subsequent tanks showed improved MPG:


Something else to get used to is making sure the car is off when you park. Even now, I find it easy to leave the car running only to be reminded by the 'beep' from time to time. Leave the car running overnight and your tank mileage will suffer.

Bob Wilson

 

You don't really need to "baby" the gas pedal (or drive like a senior citizen) to get great MPG's. In fact, sometimes "babying" the car will result in suboptimal MPG's (and annoy the living bejeezus of folks around you).

Getting up to speed briskly (not flooring it, but not going slow either) is considered one decent way to improve MPG's. The thought is that the engine is more efficient under a load, and a brisk acceleration will put it under a load. Once at your desired speed, you can back off the gas pedal and your MPG reading will shoot up.

The real trick is giving yourself room from the person in front of you and to train yourself to look well ahead of you as you drive. Anticipate when you'll need to slow down (brake lights of freeway traffic ahead, traffic lights turning to red) and let off the gas pedal earlier. The typcial advice you'll see is "drive it like you don't have brakes". It will help your MPG's as well as lengthen the life of your brake pads.

But probably the best advice is to "just drive it" for the first few tanks. You get familiar to the car and see what "just driving it" will get you MPG wise. Then you can switch to the MPG video game, trying to change your driving style to see what techniques you can use to improve MPG's as well as adjusting your driving style and behaviors.

Other things that will help would be something as simple as measuring your air pressure in your tires (get yourself an air pressure gauge) and add additional air above the recommended air pressure. The tires will tell you what the max cold air pressure is (likely 42 - 44 psi), it is very safe to fill it up to those values (actually, the tires can take wayyyyy beyond those (double? triple?) without issue. You may compromise ride smoothness for MPG's by raising the air pressure. I run my tires at 44 psi front, 42 psi rear, and have not noticed a difference in ride comfort.

Good luck and happy driving!

 

Seriously, try "rebooting" by disconnecting your negative batter terminal. Mine had immediate impact!

 

I know you've answered many of the questions I pose at http://priuschat.com/forums/gen-iii...-answer-these-questions-esp-if-youre-new.html, but can you answer some of the ones haven't been addressed?

You can skip the stuff about the state, region, and 12 volt battery and obviously the last question.

What's really important is the trip length. Short trips, esp. in city traffic and stop in go will kill your mileage. It sounds like you have pretty short trips because I deduce that in 2 days, you've only driven a total of 23 miles. Is that right? How long in time and lengths were each of these trips? About how long was the car turned off in between each?

I totally concur w/post 2, 4, 8 and what Codyroo says. Babying it can actually hurt your mileage.

 

your first MPG tank will always be lower. For one, i seriously doubt the tank was full when you drove it off the lot. The dealer probably left the car on idle for hours. When i took delivery of my car, the MPG read 22 mpg. When i filled the gas tank, i had drove 501 miles.

Your method of calculation is faulty. It's not really 38.3 mpg. Wait until you fill your gas tank and measure it that way. And as you drive, your mileage will improve as your habits adapt to the prius and the engine breaks in.

And to the above post, there is no such thing as 89 octane gas. To get 89 octane gas, gas stations mix 87 and 91 together. Also the definition of octane is simply a gasoline's resistance to engine knocking.

Octane also has NOTHING to do with energy content. Octane is simply the measure of how easily the fuel will ignite. Lower octane gasoline will ignite easier than higher octane gas, which is why hi-performance/compression engines need high octane gas beacuse low octane gas will pre-ignite, causing "knocking." IT has ABSOLUTELY NOTHING to do with energy content. That's why in higher altitude states they sell 85 octane gasoline. There is less oxygen up there, so the fuel won't ignite as easily. And i'm pretty sure people in colorado are still reporting the same MPG as someone on the california coast.

Okay, i lied. After doing some research, higher octane gasoline has a somewhat higher energy content than lower octane gasoline. But according to every expert i've read, the difference is very minimal, and almost impossible to notice while driving. The reason why somebody would get less mileage using lower octane gas instead of higher octane gas is because if their engine was designed for high octane gas, then using lower octane gas would force the engine's knock sensor to retard the engine timing, therefore compensating for the pre-ignition. Reducing your engine timing usually decreases horsepower, usually decreasing fuel economy.

How do i know this? used to drive an infiniti. Required 91+ octane gasoline, although i occasionally filled 87 or 89.

 

Ding ding - we have a winner!

-Brad

 

Also keep in mind if the dealer filled your tank with "free" gas it probably wasn't really full. Based on the numbers you have posted so far I expect you to be a very happy owner in a few weeks.

EC vs Normal mode will not make a noticeable difference in your mileage. Pick the one that makes the car feel best to you and suits your way of driving. I tried Eco for a few weeks when I first got mine and couldn't get used to that 80s Yugo feel. I use normal exclusively now.

 

The only time I get 50+ MPG is when I give the kids the car for trips to LA (Disney Land Visiting friends) I average around 40MPG but I also drive with a heavy foot and Im not really concerned about the overall milage. My second car is a 400hp mustang so 40MPG looks great to me. Enjoy your Prius it's a great car.
Regards,
Jim