Thursday, September 18, 2008

How to Maximize Your Prius Fuel Economy - By Rick Kearney

If you own a Toyota Prius, one of the most important issues on your mind is most likely, “Why am I getting less miles per gallon than the car is rated for?”

The answer is actually quite complex. The solution is not.

The first point to remember is that the EPA mileage estimates are derived using pure gasoline. Consumer gasoline (that which is available on the open market for general use) contains up to 10% Ethanol. You can do nothing about this. EPA estimates are also done on a test track, not in “real world” driving situations. They do not take into account traffic, trains, weather, other drivers or the countless other factors we encounter in daily life.

Here are some tips to help maximize fuel economy. They are geared primarily for the Prius, but most work just as well on other cars.

Tip #1. Inflate your tires. Low tire pressure causes increased resistance and wastes fuel. Low tire pressure also causes excessive edge wear on your tires, shortening their life.

This sticker is located on the driver’s door opening. Note the recommended pressure is 35 front and 33 rear. This is the MINIMUM pressure that should be in your tires. On the sidewall of the tire is another number, 44 psi. This is the MAXIMUM pressure that should be in your tire. A tire with less pressure rides softer and uses more fuel. A tire with more pressure rides slightly harder and uses less fuel. Set your tires at 40 psi and watch your mileage increase!

Tip #2 Air Conditioning. Prius air conditioning uses electricity to turn the compressor, while conventional cars use a belt on the engine. When the compressor is running, it uses power. Power that comes from gasoline. Automatic air conditioning means the ECU (the computer) can turn the compressor off when less cooling is needed. Set your A/C to a level you find comfortable. 76 degrees is comfortable for most people. “Lo” temp setting runs the compressor much more and uses more power. Remember, everything that uses electricity uses more gasoline. The power has to come from somewhere! The gasoline engine supplies the electricity for everything on both Hybrids and Conventional cars. Headlights, radios, blower fans, all want their share of power.

Tip #3 Slow Down and Smell the Roses. Excessive speed uses more gasoline than anything else. “Jackrabbit” starts and hard acceleration combined with hard braking wastes fuel. Prius is designed to get the best economy in the city. Slow, easy acceleration means the car needs less electricity to get up to speed and therefore less gasoline. Coasting allows the gasoline engine to turn off and not use any fuel at all! Sitting at traffic lights, the gasoline engine will also shut off and save fuel. Driving at steady speeds between 30 and 40 mph allow Prius to opportunity to make use of the electric motors and not use the gasoline engine for additional power.

Tip #4 Avoid little trips. Some people tend to drive only 1-2 miles to the store then the car sits for an hour or more. Then they drive 1-2 miles home again and again the car sits. These trips do not allow the gasoline engine to be run to operating temperature. Therefore, the engine is never shut off during the travel times! Plan your trips to make them in one big circle. Make the best use of Prius’ capabilities.

Tip #5 Lighten the Load. The more weight you carry in the car, the more gasoline needed to move it down the road. Do you really need those golf clubs every day? What about that bag of clothes you will take to the Goodwill someday soon? Every little bit helps.

Tip #6 Oil Changes. Dirt doesn’t weigh very much. Dirty oil, however, weighs more than you think. Old oil has collected dirt from your engine and holds most of the small particles in suspension. Changing your oil can improve your fuel economy. Regular maintenance is important.

Try these tips and track your fuel mileage the proper way. Fill your tank and record the mileage on the odometer. Drive until empty then refill and record the mileage again. Calculate how many miles driven divided by the number of gallons of gasoline pumped. That is your proper mileage. Get 6-8 readings and find the average. Remember to always stop pumping fuel when the pump clicks off. Do not top it up. Be consistent.
And always remember to drive safely!

-Rick Kearney is one of three Toyota Certified Master Diagnostic Technicians at Earl Stewart Toyota and the dealerships Resident Hybrid Genius. Rick travels with Earl regularly on the Lecture Circuit dispensing advice and answering questions for Florida consumers about their vehicles. Rick is now in the process of training Palm Becah County first responders about hybrid vehicles so they may safely conduct their rescue operations.


  1. Are you truly telling people to overinflate their tires, above the vehicle manufacturers recommendations? Just because a tire is rated for 44 psi doesnt mean it should be filled to that level. Overinflation reduces road grip and traction, as a greater portion of the tread is not in contact with the road. How can you mention "rides harder" but not mention decreased traction?

    I would like to hear Toyota's official stance to a Certified Master Diagnostic Technician telling customers to inflate their tires above their recommended pressures.

    And this is appearing on consumer guru Earl Stewarts blog?

    1. The air pressure numbers on the door of your car is to give you maximum comfort during your ride. No you should never inflate your tires to the max pressure because as your tires warm up air expands, however my tires on my prius are rated max 51psi and putting just 30 in them is essentially running them nearly halfway deflated

  2. Dear anonymous skeptical of inflating tires over manufacturers' recommendations,

    Yes, indeed, we do recommend inflating tires above manufacturers's recommendations to improve fuel efficiency...Prius tires as well as all other tires.

    The manufacturers' recommendation that is usually posted on the driver's door jamb is the MINIMUM PRESSURE for your tires. If you look on your actual tires, you will see another PSI number by the tire manufacturer. This is the MAXIMUM tire pressure.

    I believe that manufacturers recommend the minimum pressure because it gives a smoother ride. With gas prices at historic highs, sacrificing a little smoothness that can give you 5% better gas mileage is a good trade off. You don't have to inflate your tires to the maximum [never inflate them above], but 3-5 pounds over the minimum will save you a lot of money in fuel costs.

    If you would like to ask Toyota what their opinion is please do so, my guess is that they agree 100% with me. You can call them on their toll free number, 800 331-4331.

  3. Hull-Dobbs is Dead, Heard is out, My father started selling cars in 1955 bought his first dealership in 1965, I was 5 and grew up in the dealership and I was good at it. Saw your article in automotive news and relate to your sons outlook. Things have changed, but the dealers and factories don't want to. I ussually buy my vehicles through friends I have known for ever, but sometimes I stop at dealerships just to get a chuckle from car salesmen that still believe the public is ignorant, by the way I bought a camry hybrid from a friend of mine (mainly to run some miles on and for resale)If ford and GM were smart they buy some of these and figure it out, 35 mpg all the time and as high as 42 and squeel the wheels all the time. If you watch the news you know things change quick so keep listening to your Kids they probably are on the right track, repeat and word of mouth is where it is at. Maybe wallstreet will figure that out

  4. Dear "Hull Dobbs is dead",

    Amen...may God rest his soul.

    Thanks very much for your support. I agree that Hull Dobbs is dead but his ghost still hunts the showrooms of too many car dealerships.

    Few people realize that a major factor in the demise of Bill Heard's Chevy empire were his slimy sales tactics and advertising. I don't know this, but I suspect that his deception extended to the way he did business with GMAC and Chevrolet which why GMAC pulled the plug. As you probably know, GM named him the "GM Dealer of the Year" in 2004. How's that for hipocracy and it just goes to show that volume trumps ethics in Detroit.

    It's not too far a stretch to compare Bill Heard Chevrolet to Lehman Bros and AIG. Wall Street applauded these behemoths for years because of their huge profits, not caring to find out how these profits were being made.

    I'm afraid we're going to see lots of "Bill Heards" go down before this thing shakes out.

  5. My father sold his dealership right before he pasted away about two years ago, we thought hard about keeping it and I could of purchased it, but thought things might get worse before better, called that one right. I surmise that your no document fee aproach is going to appeal to a more informed and also more affluent buyer who in these times will be able to get credit or will pay cash.
    a couple of my fathers quotes sticks in my head "you can sell anything if you have financing" and "all factory cares about is moving iron"

  6. Should have been named "How To Maximize Your Fuel Economy And Risk Loss Of Traction Leading To Serious If Not Fatal Accidents!" Yea, great suggestions! And allow me to correct your ignorant understanding. Allow me to correct your "Lead Master Diagnostic Moron"!

    Because tires are designed to be used on more than one type of vehicle, tire manufacturers list the "maximum permissible inflation pressure" on the tire sidewall. This number is the greatest amount of air pressure that should ever be put in the tire under normal driving conditions.
    The recommended tire inflation pressure that vehicle manufacturers provide reflects the proper psi when a tire is cold. The term cold does not relate to the outside temperature. Rather, a cold tire is one that has not been driven on for at least three hours. When you drive, your tires get warmer, causing the air pressure within them to increase. Therefore, to get an accurate tire pressure reading, you must measure tire pressure when the tires are cold or compensate for the extra pressure in warm tires. Manufacturers of passenger vehicles and light trucks determine this number based on the vehicle's design load limit, that is, the greatest amount of weight a vehicle can safely carry and the vehicle's tire size. In other words; Manufacturers recommend this number because they know what they're doing.
    Now, if Earl and his little pet Rick want to argue over the DOT and NHTSA (National Highway Traffic Safety Admin.) I wouldn't recommend doing so publicly. What you SHOULD be doing is educating and informing customer's properly in regards to safety. Not how another jew-bagel can pinch-a-penny! In my opinion safety supersedes gas mileage.

  7. Dear "anonymous anti-Semite",

    I won't bother to respond to your completely inaccurate comments about tire pressure and manufacturers's standards.

    I thought you might be uninformed when you began your comments by calling Rick Kearney, a Toyota Certified Master Diagnostic Technician, a "moron". His training and knowledge rank him in the top 1% of all Toyota technicians in the USA. I wonder what qualifications you have. Did you make it through elementary school?

    You fulfilled my suspicions that you were totally ignorant when, at the end of your rant, you revealed that you hate people of the Jewish faith.

    Now I see why you want to remain anonymous... most anti-Semites prefer to cloak their hateful ignorance.

  8. Section was a pretty good article. I just found your blog and really enjoyed reading your blog posts. Any way I will be subscribing to your feed and I hope you post again soon.

  9. After 40,200+ miles, I am about to replace thed original tires on my 2012 Prius which has consistently averaged 56 MPG @ 40 PSI.

    I have researched several brands and styles and am between Michelin Defender and Michelin Primacy MXV4 tires as my choice.

    The question I have for anyone interested is this: Will a different size 15" tire possibly increase my MPG even further? And if so, what size (width?) do you recommend?

    Thank you in advance.

  10. Dear Prius Pal, You should stick with a LRR (Low Rolling Resistance) tires. Some good brands and models are the Goodyear Fuelmax, Bridgestone EP422, Toyo Versado Eco and the Cooper CS5, the Michelin Energy Mxv and the Energy. You should give them up to 1,000 miles to "break in" before you will be getting your maximum fuel economy.

  11. Hi Earl, the winter tires for my Prius C are rated 40psi max. I've set them 38/36. What is your recommendation?


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