Dan is a "backyard mechanic" who has always done his own auto repairs whether on motorcycles, boats, cars, or even motorhomes.
The Ugly 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.
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
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.
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
Questions & Answers
Question: I have a 2010 Prius that I have owned from new. I live in Arizona. The last three years during the hotter months, I only get 200-250 miles per tank. Toyota will do nothing. They say the computer says nothing is wrong, so it's fine. I complained to Toyota manufacturer, and they laughed and said there is nothing they can do. My Scrambler gets better mileage than a hybrid. Do you have any suggestions?
Answer: If you haven't changed the small 12-volt battery used to start the car, do so. This article, https://hubpages.com/auto-repair/How-to-Change-A-P... will give you detailed instructions on how to do so.
As that small battery goes bad, the car continually tries (hard!) to charge it, but it simply will not hold a charge. That takes energy - energy that is coming from the engine. I didn't lose as much mileage as you have, but there was a very definite improvement after replacing that small battery, and it wasn't as old as yours is.
You might want to have your air conditioner looked at, too. That's going to run, and if something is wrong, it could conceivably cost more fuel to operate.
Question: I have a 2009 Prius with 108,000 miles and have been only averaging about 36-37 MPG over the last year. Even after an oil change, I have not seen any appreciable changes. I live in South Florida and run my A.C. nearly year round, but even still, this seems like an exceptionally low MPG. Any suggestions?
Answer: Yes, AC will most definitely affect your mileage, but just as you say it shouldn't be that much. You didn't say, but I assume it used to be higher.
Have you changed your little 12V battery? They slowly go bad, just like all batteries, with the result that the Prius tries, hard, to charge it up all the time. That might be something to consider - it is used primarily to click on the big relays to the high voltage battery, but that's about all so it isn't like the battery in other cars that you know is going bad because the starter will barely turn over. I know I saw the same big mileage drop at about the same time you are and replacing that small battery took care of most of it.
Again, you didn't say, but new tires will also hurt although to do so for a full year seems unlikely.
The only other thing is to take it to a shop for a complete check-over. A tune up on the engine (new plugs, air cleaner, etc.) and to look for anything else.
Question: I was wondering whether you had any experience in using the B-mode in a more recent Prius. I just got a 2018 Prius Eco, and I´m not sure under what circumstances the B-mode helps to conserve fuel. Is it only on extended downhill sections, or can it be used as a regular setting for the city or highway?
Answer: I do not. But you should consider that any energy coming out of that battery will be replaced by burning fuel unless it is a plug-in hybrid. Given that, I don't see a battery only mode saving much at all. If you're changing parking spots, or in a slow line getting out of a parking lot, it might help conserve a little.
© 2010 Dan Harmon
Dan Harmon (author) from Boise, Idaho on September 06, 2019:
It is pretty much the same thing; as there is no real transmission in a Prius, the "B" simply re-maps the instructions for what happens when the throttle or brake is applied (or not). It does not shift gears as most cars do.
Some people drive all the time in "B", thinking that the increased regen will improve mileage, but all that does is make you use more gas for longer periods until the throttle is let off.
Nick on September 05, 2019:
B-mode: I have B-mode (2012), together with R and D. B is for engine-brake when you go downhill. I wonder, if this is the same thing,
Dan Harmon (author) from Boise, Idaho on March 18, 2019:
I can't answer that question definitively, but the HV battery is not charged to absolute capacity in normal operation; there is always some capacity left in it. This is done to prolong the battery life.
I would suspect that regen braking would utilize that extra capacity to some extent, with the result that in normal operation the energy is collected and saved. There will obviously be a point where that is not true, but it would be rare to see it. A very long, very steep down grade perhaps.
mgb on March 12, 2019:
Interesting about the 12v battery hurting mileage. For unknown reason even when very careful, my 2006 Prius rarely averaged over 50 mpg, and the dealer could not help. I even avoided using the heater in the winter. Question: After the HV battery shows as full, is regen (and other) energy wasted that otherwise would charge it ? ... and, is there a way to capture it ?
Dan Harmon (author) from Boise, Idaho on August 16, 2018:
Some good thoughts, Ed: thanks. I will point out, though,that using the "braking mode" accomplishes nothing that using the brake pedal doesn't; it simply re-maps the computer response to the brake (and coasting). It IS useful, though, to maintain cruise control down steep hills as simply coasting, without the brake, slows the car more than normal.
Ed Brown on August 10, 2018:
I think the previous question was about "braking Mode", not battery only. Braking mode on the shifter of my 2005 is handy when decelerating to stops and going down steep hills. I have climbed one side of a mountain and drained down to two bars and then totally regenerated a full battery in braking mode going down the other side. You overlooked a couple obvious savings points: oil and air. Make sure the oil is not overfilled (as most lube businesses will do) or it can cause resistance by interfering with the crank and pistons. I found that a change to synthetic oil also gave a small increase in MPG and I believe it is worth the difference in cost. Plus I change the oil at 7000 mile intervals instead of 3000, as instructed by the synthetic oil manufacturer. I also gained a little by installing a higher flow rate air filter (K&N) that is reusable: savings on cost of filters alone paid that one back quickly and I believe there was a small increase in MPG due to decreased air intake resistance. Between 5000 miles and 75000 miles, I was getting 55-62 MPG after the oil and filter upgrades and burning California fuel mix. Now around 90000 miles I am getting 45-50 MPG doing the same highway/city driving. I figure the age of my traction battery is more a factor now and I have had it in some harsh heat and freezing conditions.
Dan Harmon (author) from Boise, Idaho on June 06, 2018:
If done properly, nothing you list as being done will produce a decrease in mileage. I would contact the repair shop for a double check on the work and their recommendations.
Hassan on June 06, 2018:
My prius 2008 was excellant in fuel consumption with 56mpg and then i get it tuned by replacing plugs, cleaning throtle body, and over all cleaning and to my astounishment the fuel consumption increases to 43mpg..what could b the problem?
Peter on May 30, 2018:
Thanks for the answer, Dan. I will check on the 12v battery. To answer a couple of your questions, I changed all four tires around six months ago; and yes, for the first 5-6 years or so, I was getting 45-50 MPG on the HIGHWAY with a 71 mile commute EACH WAY. I am going to do as you suggest and bring it into the shop for a look. Thanks, again!!
Boomer on February 24, 2018:
If you are going to mention Atkinson Cycle and Otto Cycle, why not explain what they are? At least list links for more information on them. What is the point of mentioning them if you aren't going to provide a better explanation of what they are? Your article has good information but could be better.
Boomer on February 24, 2018:
I don't think the car is ugly at all.
Dan Harmon (author) from Boise, Idaho on August 10, 2017:
Sorry, naeem, but I can't help you there. Suggest you visit the toyota website or download a copy of the owners manual. That should give the required maintenance.
naeem on August 10, 2017:
pls guide for 100000km maintance of 'Toyota AQUA' PLEASE.
Dan Harmon (author) from Boise, Idaho on November 24, 2014:
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.
Emilia Riera from Philadelphia, Pennsylvania on November 24, 2014:
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.
phillygal on June 21, 2013:
Thanks for your thoughts. Just found this site - http://www.prius3.com/specs/four-driving-modes -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.
Dan Harmon (author) from Boise, Idaho on June 21, 2013:
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 on June 21, 2013:
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.
Dan Harmon (author) from Boise, Idaho on April 20, 2013:
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.
rah on April 20, 2013:
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.
Dan Harmon (author) from Boise, Idaho on March 31, 2013:
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 on March 31, 2013:
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.
Dan Harmon (author) from Boise, Idaho on June 07, 2011:
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.
Anthony on June 07, 2011:
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