How To Get Better Fuel Economy From Your Prius

The Ugly Prius

"Sandy", our 2006 Prius
"Sandy", our 2006 Prius

Better Fuel Economy for the Everyday Prius Driver

This article is dedicated not to the hard core hypermiler, but rather to the everyday Prius driver that wants better fuel economy, or higher mpg, from their Toyota Prius. The Prius is currently the premier high mpg car in the US, but even so that already high mpg can be raised by understanding a few basic tips. Better fuel economy does not come from magical water injectors or from perpetual motion devices, but from careful driving and a good understanding of the operating principles of your car. The Toyota Prius hybrid car is different enough from normal cars of the past that it can pay off handsomely to do a little research on some of these differences.

Basic Differences With the Prius

Obviously, the Prius is an electric hybrid car—I'm sure you knew that if you already own one. What you may not realize are the economies that are possible as a result of those differences; just how to properly use those differences to achieve higher mpg figures takes a bit of study.

The Prius contains a high voltage, high capacity battery capable of propelling the vehicle to slow speeds (42 mph) without the use of the gasoline engine by using a pair of electric motors. Please note the nomenclature; "engine" refers to the gasoline engine while "motor" refers to the electric motors. I will be using these terms throughout the tutorial.

The engine in the Prius is different than ordinary car engines in that it is designed around the Atkinson Cycle rather than the normal Otto Cycle engine used in other automobiles. It is designed and tuned for efficiency and better fuel economy rather than power and has different operating characteristics.

The brakes on the Prius normally operate via regeneration - a term used to indicate that the energy of motion is being converted to battery power as the car is slowed. Actual brake pads, similar to other cars, are also used but only in very hard stops and below 7 mph where regeneration is not practical.

The transmission in the Prius is known as a CVT (continuously variable transmission) and has no "gears" as we think of them. The only shifting is between drive, neutral and reverse and in neutral and reverse the engine is shut down and motion is accomplished by the electric motors and/or momentum.

Finally, the Prius is designed for two things; better fuel economy and a minimum of pollutants. These two items are not mutually incompatible, but they do affect each other and those effects need to be taken into consideration.

These differences need to be taken into account when considering just how to get better fuel economy, and require different discussion at highway and urban speeds.

Charging a low battery while getting only 26 mpg.
Charging a low battery while getting only 26 mpg.

Prius Fuel Economy for the Highway

Although the Prius is classified as a mid-sized vehicle it is designed primarily for the urban environment. Nevertheless there are a few actions you can take to get better fuel economy when highway driving.

First on the list, of course, is to slow down. While the Prius has a lower air resistance than nearly any other car, it is still applicable and fuel economy goes down rapidly at higher speeds. I seldom drive over 70 mph and never over 80. For a 200 mile trip the difference in time required is only 30 minutes when going from 80 mph to only 65 mph and the difference in average mpg is quite large. Slow down and enjoy the drive more.

Maintain a constant speed, especially on flat ground. Changes in speed cost fuel and that fuel usage cannot be overcome. Cruise control is a great option - use it whenever possible.

Much of my own driving is through mountainous areas, however, and I find that a little better fuel economy can be found by accelerating slightly uphill. This flies in the face of common sense, but there is a reason for that in the Prius. The Atkinson engine is carefully tuned to operate best at a particular engine speed, about 2100 RPM. On most hills, this engine speed will not be reached and the engine will not, therefore, operate at peak efficiency. Without a tachometer, you cannot tell what the engine speed is, but a good rule of thumb is to keep the instantaneous mpg figure on the energy screen to about 1/2 of the speed. In any case you should pick a top speed that you will attain and try to increase speed slowly so that speed is found at the top of the hill. On the way down, speed should be allowed to decrease slowly until the cruise control again takes over. Do not allow the car to coast on gentle hills (green arrow on the MFD), but keep the engine running just enough to slowly shed speed. You may find on some hills that the engine will shut down and run on battery only. Practice will tell you what throttle setting is needed for different grades.

I find that I average around 45 - 50 mpg on the freeway. A little disappointing to me, but I drive in mountainous areas and that always costs extra fuel. In addition it usually windy and that also hurts. I normally drive at 70 mph and I realize that some savings could be saved by slowing down, but that is the choice I make. I usually have either the heat or AC on and that also costs, but is again a personal choice. My comfort is more important than saving 50 cents on my trip.

MFD Screens Relating to Fuel Economy

Engine on, charging battery
Engine on, charging battery
Engine off, no battery usage.  The preferred screen.  Note the speedometer in the upper left of the photo.
Engine off, no battery usage. The preferred screen. Note the speedometer in the upper left of the photo.
Engine off, regenerating energy by slowing down.
Engine off, regenerating energy by slowing down.
Running on battery; the screen to avoid when possible.
Running on battery; the screen to avoid when possible.
Results achieved - 20 minutes at nearly 75 mpg + 5 minutes at 45 mpg during the warm up cycle.
Results achieved - 20 minutes at nearly 75 mpg + 5 minutes at 45 mpg during the warm up cycle.

Fuel Economy in Urban Areas

This is where the Prius shines, and by far where the better fuel economy is achieved. I always reset the mpg counter when I fuel up and while I have achieved as high as 65 mpg for a tank, my normal average is around 53 mpg. It also includes driving done by my wife, who makes no effort to increase her economy and always hurts my average.

Tip #1 - Do not drive on battery alone! I realize that this is again counter intuitive, but there is a good reason - 100% of the battery charge you are using by driving on battery alone is achieved by the use of gasoline, and there are always energy losses in every system. Even regeneration by braking requires gas to get to the speed you are slowing down from. I make one exception to this rule; the last 3 or 4 blocks into my home. By using the battery here I leave the battery in a discharged state, but it is a state to be recovered from the next morning. You see, the Prius computer will run the engine on start up to warm the emission system to its operating temperature. You have probably noted that after a few seconds you cannot drive on battery in these conditions; it is because the computer is requiring the engine to run whether it actually needs to or not. There are other exceptions, of course; to impress your new passengers (always fun!) or to move quietly from a garage or parking area. Such things won't cost you much, just don't do it as a matter of course because you think it saves fuel. It doesn't.

Instead, drive with the engine off without using the battery. Watch the MFD; the blank screen with no arrows is the one you want. The preferred method is to speed up to a little more than is actually desired, then let off the throttle. This will produce regeneration, or the green arrows; reapply throttle slowly until the green arrow disappears but the before yellow arrow (electric motor) comes into play. The car will gradually slow down; I let it happen until it reaches about 5 mph below what I really want, then repeat the process. Progress down the road is a constant variation in speed, from 5 mph under to 5 mph over my desired speed. During acceleration the instantaneous mpg is again held to about 1/2 of the speedometer reading, just as it is done in climbing hills, as that gives the best approximation of the ideal speed of the gasoline engine.

Tip #2 - Maintain your speed. No, I'm not talking in circles; what I mean by that is don't slow down or stop any more than necessary. Try to time stop lights so that you don't stop; slow down (using the "no arrows method) ahead of time so that you drive through them as soon as they turn green without stopping. If a car in front you slows to turn, slow down earlier in order that you maintain as much speed as possible and drive by the other car at as high a speed as possible.

Tip #3 - Try to plan your trips so as to not make any more stops than necessary. Even warm, the computer will run the engine unnecessarily each time it starts. I go to yard sales a lot; if possible I will leave the car on at each stop. The engine doesn't run while stopped and there is no "startup" cylce to worry about.

Tip #4 - If you live in a cold climate, consider purchasing a block heater to help keep the engine warmer; it will come to operating temperature quicker each morning.

Finally, whether you are driving in the city or country, keeping your Prius in good mechanical condition will pay dividends in fuel mileage. On thing that most people ignore is the small 12 volt battery, but as that battery ages and becomes incapable of holding a charge it will affect your fuel mileage. If necessary change the battery out for a new one before it begins to go dead on a weekly basis.

Try these tips in your own Prius; I assure you that they will work and will increase your fuel economy. I also find it fun to the get the most I can out of my car - to use it more nearly to its maximum potential.

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Comments 11 comments

Anthony 5 years ago

Great tips, I love my Prius and I already apply most of your suggestions. I am also in the process of installing a Plug In kit on my car, expensive but worth the effort if we can reduce or oil dependance. I have found an even better way to save fuel, especially on short urban trips - use a bicycle! The cheapest fuel is the fuel you don't use...

Anthony from France

wilderness profile image

wilderness 5 years ago from Boise, Idaho Author

Like you I very much appreciate my Prius and would love to have a plug in kit. I understand that they are currently testing a new model built as a plug in - perhaps it will be ready for sale by the time I'm ready to trade mine in.

Can't use a bicycle for better fuel economy, however. Most of my trips are at least 20 miles one way and usually requiring carrying several hundred pounds of hand tools with me. A little difficult on a bicycle.

Rah 3 years ago

When going down a hill, use just enough gas pedal to get the energy bar to use all of the battery power and no gas to pick up as much speed as possible so that the gas engine won't come on until your on your way up the next hill. When you don't do that, the gas engine comes on at the bottom of the hill. Every little bit helps. I got 60 mpg on 3 consecutive tanks of gas. My best overall recorded mpg is 60,1 driving 476 miles. I also drive 60mph using cruse control.

wilderness profile image

wilderness 3 years ago from Boise, Idaho Author

I don't think I could do that - typical "hills" around me are a 7% grade. I'd be going 150 mph at the bottom! Instead, I've usually got the battery completely full at the bottom, and it really helps on either a following hill or flat - if flat I can often get 2 or 3 miles at 65mph with little to no gas.

That's pretty good mileage, and more than I've ever gotten. Almost all my travel is through mountains and that hurts no matter what you do, especially as I often fight a good headwind through the passes. I do see a solid 50+ almost all the time, though - just a very occasional drop when I've got 50 mile trips almost all uphill.

rah 3 years ago

Think outside the box. Let the re-gen. braking happen half way down the hill and then use all the batt. power the rest of the way down the hill to be able to go up the following hill a certain distance before the gas engine comes on.

wilderness profile image

wilderness 3 years ago from Boise, Idaho Author

Rah, it takes a pretty steep hill to use regen without slowing down. It also takes a very gentle hill to use battery only to climb.

However, I have found that long steep downhills (at highway speeds) will charge the battery enough to use next to no gas on the level; a mile or even more can often be traveled even at high speed while maintaining 90+ mpg. The gas engine is running, but at a very low gas usage.

Never forget that it actually costs energy to force charge the battery and then draw it back out. Using regen while allowing to car to slow, and then using that charged battery to speed back up is not efficient.

phillygal 3 years ago

I am a new Prius owner, 2010. I love my car, but my gas mileage is going

down, and I don't know why. I thought I was driving efficiently, but apparently not. It has topped out at 50 mpg, and is now down to 46.6 mpg.

I do a lot of short trip driving - 3 minutes to the supermarket, 5 minutes to the cleaners. Any suggestions would be greatly appreciated. Also, should I be driving in Eco mode most of the time for best mileage? Thanks.

wilderness profile image

wilderness 3 years ago from Boise, Idaho Author

Your short trips are definitely hurting you. While the Prius is designed for best mileage in town, during the first few minutes the engine will run whether needed or not simply to heat up the catalytic convertor to operating temperature. It is possible that driving a couple of blocks and then going home might do better on battery only. It will cost gasoline in most cases, but might be worth a try for very short trips.

I forget the terminology in the newer Prius. I think eco mode is the most efficient, but if it means to run on battery only, don't do it in most cases. That's useful only if you're going to back the car out of the garage or need "silent running" for some reason. Getting away from an apartment complex early in the morning, maybe.

There are other things as well - I recently put a new set of tires on and promptly saw my mileage drop over 5 mpg. Rainy weather will hurt, or extremely hot weather from running the AC. In general you can expect better mileage in the summer vs winter, but that won't hold true all over the country because of that AC going - southern states could well show the opposite.

phillygal 3 years ago

Thanks for your thoughts. Just found this site - -which explains the 2010 driving modes. Eco mode is different from EV mode - I guess I'll need to familiarize myself more with the terminology and play around with how I drive.

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Emilia Riera 23 months ago from Philadelphia, Pennsylvania

I've owned a Prius for 9 years. After the first year, the fuel economy went down significantly. It took it back for a tune up, but the dealership insisted nothing was wrong with it. Originally, I got 50 mpg in city and 55-ish hwy. Now, I get about 45 mpg combined, 40 mpg city alone. During the winter, it plunges more. I can get as low as 35 mpg. I assume this is because of the extra drain on the battery - lights, defroster, heater, wipers, etc. Thanks for this interesting article.

wilderness profile image

wilderness 23 months ago from Boise, Idaho Author

Yes, the mileage will go down in winter. Partly because the engine runs more simply to heat itself and the catalytic converter, but also because of adverse conditions. Snow or slush, for example, requires more energy to plow through (I can even tell when I've driven through a lot of rain). The accessories cost energy, but not nearly as much as to move the car or to plow snow.

Tires will also make a big difference; new tires always show a drop and although the OEM tires are great for mileage they are not so good for longevity or traction. Most people choose a different tire - when I did there was an immediate drop of around 6 mpg.

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