My Toyota Prius, gas mileage and altitude

I’ve had a fascinating experience with my Toyota Prius in the last few months and am curious whether other Prius or hybrid owners have experienced similar: The Prius gets significantly better mileage in lower altitudes.
Here’s the scoop: I live in Boulder, Colorado, at approximately 5300 feet elevation (just a smidge higher up than Denver, the “mile high city”) and on average, we see about 39MPG driving our Prius around in town and occasionally to Denver or the Denver International Airport. Not too impressive and a far cry from the 60MPG that Toyota claims in its advertising.
I’ve even taken the car in to Toyota for a checkup. They’ve run a full set of diagnostics, checked all the firmware and applied all the latest patches, etc., but there was nothing they could find that indicated anything out of the norm. Their great solution? We were driving it in a way that was adversely impacting our mileage.

However, I have spent most of June and July at the Lake of the Ozarks in mid-Missouri, altitude approximately 900 feet above sea level, and guess what?
We’re seeing approximately 46MPG on average for a tank of gas, even with the hills in Missouri (lots of rolling hills), the greater load than usual (in Boulder its usually a driver-only vehicle, in Missouri we’ve had the kids in the car most of the time), the same two drivers (my wife and I) and roughly similar road conditions.
I thought that perhaps it was the octane level of the gas, because in Colorado we have lower than normal octane because of our higher altitude. That might be a factor: I’m going to experiment with using mid-range gas now that I’m back in Colorado, but I’d be surprised if the octane level would make a difference and I certainly haven’t ever seen anything to that effect when I’ve poked around online.
Therefore, the only other possibility I can imagine is the altitude.
But how can that be? How can a difference of 5000 feet of altitude impact the Prius so much that our mileage drops from 46MPG to 39MPG on average?
Have any of you fellow Prius or hybrid owners heard of anything like this before? Is there something I can do to tweak our 2004 Prius (first year of the second generation design) so that the fuel mix / carb / fuel injection / whatever is optimized for our higher altitude?
I was shocked by the difference, quite frankly, and really wonder whether this doesn’t point to a significant limitation with hybrid vehicles in Colorado and other high-altitude areas too.

47 comments on “My Toyota Prius, gas mileage and altitude

  1. I believe you loose about 3%/1000 ft through altitude so a Prius would loose about 11hp from the petrol engine. Since it’s underpowered to start with, + the octane hit, you’d see the impact in your mileage. Especially if the batteries take a hammering and force more petrol motoring

  2. Hi Dave,
    I guess you don’t fly aeroplanes…
    The higher you go, the less dense the air is, so the less “air” it contains for a given volume. I don’t know much about how fuel injectors work, but I guess Robin is on the right track. Because the air is thinner, you have less power in the petrol engine, so you’re having to work it harder – thereby getting worse economy.
    It’s just that probably not many people measure their mileage regularly, or are observant enough to notice a correlation between mileage and altitude.
    Hey. Aren’t *you* supposed to be the one answering the questions around here?

  3. Gasoline engines lose efficiency as you climb in altitude due to less oxygen in the air. While people have a harder time breathing until they become acclimated, cars can’t adapt (unless you add a turbo or supercharger).
    All naturally aspirated vehicles (non turbo, supercharged) experience a distinct change in both power and efficiency at higher altitudes, even race cars.
    Your Prius actually gives you an advantage, performance wise, as the electric motors and battery don’t suffer at higher elevations. Driving dynamics and performance will remain close to those at sea level, unfortunately the fuel economy doesn’t follow suit.
    Hope that helps…

  4. I would typically recommend adding a small amount of acetone to the gasoline, ( 1oz./4 gals. or 3 ounces for 12 gallons), as this will boost your MPG in most cases by 3-20%, depending on the vehicle.
    However,there would be a problem using acetone with a Prius, as it turns out that the Prius has a bladder lining in the gas tank, which could be damaged over time by the solvent effect of the acetone.
    See more here:
    … where a wiki poster notes the problem with the potential for damage if acetone was used to boost the MPG by stating the following:
    Toyota Prius gas-tank lining issue
    “! ! WARNING ! ! The TOYOTA PRIUS has a synthetic bladder lining to its gas tank. Although I am an big advocate of using acetone in your gas, I’ve heard & read instances of acetone reacting with the bladder. — User:Winnix (June 18, 2006)”
    So, I thought I had a solution for you, but it turns out that it would not work for the Prius.
    I do wonder if a new air intake would help, though. Many Mazda and Isuzu owners add custom aftermarket cold air intakes to increase their HP, and this might be an inexpensive thing to try that could work as a workaround by supplying more intake air to the engine. Not sure if such will fit under the hood of the Prius, as the engine compartment is pretty tight with little room to spare, but it might be worth investigating.
    As for us, my wife drives an 07 Prius in central Florida, at 65 ft. above sea level and we get about 49 MPG pretty consistently.
    Good luck.

  5. Dave –
    Toyota can’t claim 60 MPG now that the EPA has rolled out its revised mileage estimates. The current EPA estimates for the Prius are 48 MPG city, 45 MPG highway, and 46 MPG combined. Alas, you’re a bit more than 10 percent shy of that. It might be the altitude or it might be the route you drive.
    I noticed a biodiesel pump at a service station when I was in Boulder this spring. Maybe it’s time to trade that Prius in on a fuel-sippling clean diesel that runs on domestic juice? Volkswagen will bring its spiffy Jetta SportWagen TDI to the States in six months or so …

  6. The issue may be reformulated gasoline. I have a hybrid Camry and have noticed a very significant difference in mileage between conventional gasoline (which I can get in some rural areas in AZ) vs. the 10 – 15% ethanol or MTBE junk we get in the Phoenix area. The energy content per unit volume of those ‘clean air’ additives is much less than the gasoline that they replace. So, we urban dwellers take a 10% hit on fuel economy right off the bat. Do those additives actually lead to cleaner air? No. They’re oxygen providers which might help with old carburated engines that ran rich, but not with modern computer controlled engines.
    Check your gas pump in Boulder. I’ll bet you’re getting reformulated gas.

  7. Hi
    I purchased a 2007 Prius in March 07.
    My fuel calculations after 6000 miles were 50.2MPG
    That was lifetime gallons of gas consumed.
    between 6000 and 9000 miles, I went on a roadtrip that consisted of 2400 miles of travel in 7 days.
    Between Ohio and West Virginia I got lowest mileage ever with fillup at Sandstone WV. at 35.6MPG. During that portion of the trip there were several 5 and 7% grades that seemed to go on forever.
    Now after 9000 miles my lifetime average dropped to 49.7MPG.
    Wisconsin elevation is 600ft.

  8. Hi! I too want will share the reasons in occasion of Toyota car.
    The first car was toyota corolla, volume of the engine 1.5, good car, but very weak engine.
    Car economy class. Car toyota camry, volume of the engine of 2.0 litres. Excellent car,
    but it would be desirable even more powerfully! Now I go on car toyota Surf, the engine diesel!
    That is necessary for me! 1KZ! COOL!

  9. Our family has had three Priuses over the years (one was totaled and replaced) and after nearly 200k miles in Priuses it seems there are many factors which drastically effect mileage:
    ��The weather (and temperature) is quite important � cold weather, especially when driving short distances ��causes the gas engine to run when starting which will increase fuel consumption.
    � Driving conditions matter too. Yes, the Prius does better than other cars in stop-and-go traffic, but still not terribly well. No cars do particularly well when constantly accelerating and braking (the Prius only recovers some energy when slowing � the rest is lost as heat).
    � But most important is how you drive. Hypermilers have pushed the Prius over 100 mpg. I myself have averaged 70 mpg over 60 miles. The key is that driving fast kills your mileage. Wind resistance is inversely proportionate to the square of the speed, so at 70 mph the wind resistance is about double 50 mph, and most of the energy of the car is put in to overcoming the wind. Most cars are most efficient around 50 mph, but the Prius is actually most efficient at 41 mph, above which the gas engine is spun (even when not in use) to prevent damage. The Prius is also most efficient when driven by “pulsing and gliding,” accelerating at about 2/3 of full throttle and then coasting using only the electric motor.
    But going 38 on the interstate is not practical, is it? To get much better mileage, accelerate smoothly, plan ahead (don’t accelerate down a hill if you know there is a stop sign ahead, rather coast to a stop), learn to use the brakes as little as possible, and, to truly be green, if you don’t need to use your car, don’t! Take a bike, use car sharing (Zipcar, Flexcar, Citycarshare, Phillycarshare, Igo, Hourcar, etc), take transit. It’s not too hard.
    Here are a couple of articles which might interest you on hypermiling:

  10. I have a 1994 toyota surf with a 3 liter turbo diesal, I also have a lancruiser with the same engine. The lancruiser is probably 300kilos heavier, but gets better milage, and I have put a foam air cleaner on the surf, also run a fuel conditioner in both vehicles. It doesn not smoke or lack power, so the injectors are fine. I wonder if it could be the new low sulfer fuel that has been introduced here in NZ

  11. My 1999 Metro gets 41 mpg in city driving and 50+ on the highway. And it only cost me $8000. Too bad they don’t make them anymore. But I guess they don’t have the “I’m better then you” value that you get with a Prius.

  12. My 2007 Prius, I bought in July great gas mileage 50 plus. From KC area. Now that the cold weather hit from some strange reason, besides the heater uses gas, when you turn it on. I am only getting in the 30’s now. What is this about ?

  13. I get better gas mileage between 32-50 mph. Higher speeds are at a lower mileage, if you slow to a stop or coast to a stop,and coast down hills whenever possible you will get better gas mileage where ever you live. Look for Toyota Synergy View

  14. I live in Salt Lake City, Utah at a similar elevation and have been pleased with my average 48 MPG but, I’ve noticed a significant drop since winter arrived. I’ve had my Prius since June 2007 and was consistently getting about 48 MPG. Since winter hit, I’ve dipped down to only 39 MPG. Would the cold make that much of a difference?

  15. I purchased a 2008 Toyota Prius. I live in Wisconsin and it has been very cold. I am at 900 mile and am only getting 20mpg. I have been trying to drive very conservatively for the past 2 weeks and have only gotten it up to about 26mpg. Don’t know if it is just the cold weather or if I should take it in and have it checked. Going uphill I have noticed that the engine works very hard.

  16. Yes, it was cold weather that made my 2007 Prius run 30 something, and not 40’s 50’s gas per mile.
    It’s back to the higher miles per galllon with warm temps.
    By the way Iam looking for the xm install kit for my car. Toyotoa wants 300.00 to install now way in this time I will pay that to install. Plug and go it says.
    Anyone suggest where to buy it ?

  17. My 2008 gets 54 to 60 mpg but I git to drive 56mph and follow 18 wheelers in the draft 300 ft behind them . Don’t git anycloser as they’ll have a fit, I lhave a scanner that gets CB and can hear the truck driver freaking out about if I was an undercover CHP or whatever and slowed down forcing me to pass with a faster truck. When I got around, the truck driver pulled his air horn for two mins and tailgated me until he pulled off on 152 off of 99!
    The lesson is: as soon as the trucker starts to react to your catching the draft, pull back and let him go

  18. I love my 06 Prius and get 44 MPG winter and 49 MPG summer in western Washington, I would like to see it do better so I have been looking into some littlie things to improve performance. As I was checking air filter recently I saw that the filter box had collected some maple seeds and junk from the road this can�t be good, it looks like it draws air from down low, also the air ducting is somewhat constrictive. I think the air management system could be improved.

  19. My 2007 Prius, with gas prices high more people are asking me about my car. I enjoy sharing information about not having a gas guzzler like I had in the past. I have it down to a T. Drive 38 miles per hour from stoplight to stoplight, you will be able to keep the car in electric mode, accomplishing your goal of better gas mileage.For the biggest part I get 50-60 depends on elevation of your area. Take advantage of the hills to regarge.

  20. Are you ready for this ? I have been pushing the limits with my Electric Motor on my 2007 Prius.
    I was able to keep it in total electric mode from the gas pump,to home. I only buy BP not sure if that makes a difference. My gas mileage was 76.3 4miles. Now you tell me are the Toyota people wrong.

  21. It’s been interesting reading this thread because I too am interested in buying a Prius. I’d heard the car did not do well at higher altitude (I too live in Colorado but at 9,000′). Interestingly, my wife’s Honda Pilot AND my Dodge Cummins diesel both get better mpgs at high atitude (both 20 mpg) than down lower. Keep me posted as to other comments on this thread. I’d hate to sell the Pilot that gets 20 mpg and buy a Prius that doesn’t do much better than that. Thanks.

  22. We rented a 2008 Toyota Camry ( not a hybrid) on May 23rd and drove from Albuquerque NM to Denver. The mileage was amazing. 38 and 39 mpg over 1000 miles of driving. The speed limits were 65 and 75 mph and the driving was through some mountains as well. We routinely get 28-30 on our 99 Camry at home in MD.

  23. My wife and I both drive the same car. 2008 model. I can avg. better than 50 mpg while she typically does about 45mpg. It is all related to driving habits and styles. I treat it like a game to see just how good a # I can get, whereas she drives it like a little sports car, rapid acceleration, quick stops, etc. I have found I do better to get the speed I want and then maintain it gently, drive like I have an egg under my foot, and I couldn’t be happier with our car. Makes me feel stupid for driving a big SUV all those years. We were getting about 15-16 mpg in an Expedition so my wife feels her 45 mpg is good enough, I can’t disagree.

  24. I live in downtown Denver and drive to Broomfield daily. Driving conservatively, in June, I’m getting 52 mpg in my 2005 Prius. In the winter I got 42. I get this mileage by driving the speed limit (even on 36!), braking slowly etc. Driving aggressively lowers my mpg lowers my numbers by about 20%, the numbers you’re seeing. I’m surprised that you ignored the suggestion from the dealer that changing a habit could offer an improvement, and you instead looked for an external cause.

  25. I see the exact oposite with my VW Golf (and my privious VW Cabriolet). I have driven to and from California starting and ending in PA, FL and SC. And I always get the best gas mileage in Colorado (I80) and New Mexico (I40) at elevation and driving up and down the rockies. I drive about the same speed accross the country, but always go from averaging 32MPG to about 36MPG in NM and CO(I go down the 30MPG with 10% Ethenol). I just don’t get it. I know my car is working harder getting up into the mountains and expect to get worse mileage, but it always goes up.
    Less friction because of lower air pressure? Higher tire pressure? Less power, but higher milage?
    Got me.

  26. Here is another issue to consider … your gas tank will rarely be full. If you are counting on 40, 45 or 50 MPG and expect you can use say 10 gallons of gas … you would think you can drive 400 miles at a minimum. In cold weather your tank shrinks and maybe you can only get 7 gallons in it … if you are only getting 30 MPG your range would be only about 200 miles with 7 gallons of gas … check the web for Prius problems, Prius gas tank … key words like that … issues with the car have been going on a long time … maybe you want to contact your state’s BBB, attorney generals office, consumer reports, your local news inveestagators, Toyota corporate, NHTSA … this issue is a SAFETY issue … you could be driving one VERY cold dark night and run out of gas … 🙁

  27. I just drove 800 miles in rented Prius through Grand Teton & Yellowstone Parks. On average 7,000-11,000 altitude. I experienced 57.3 mpg in first tankful and 56.5 during second. The rental company said many of their customers can get 60 average. I can’t explain this anomoly if conventional wisdom is the milage should be less at altitude. Fred

  28. Actually, I’ve seen a marked improvement in gas mileage now that it’s the hot summer months. I don’t think I’m driving much differently, but I’m averaging 45-47 MPG across my fillups. Not 60, but still not shabby!

  29. I have seen the exact opposite, and it drives me crazy. I’m driving a ’95 Camry, and I just moved from Utah to Louisiana. In Utah, and on the first leg of the trip out here, I got at least 30 mpg on the highway. Once I started getting through Texas, though, gas mileage dropped like a rock and now I get 20-25. It’s pathetic.

  30. I’ve found just the opposite. We just moved from Chicago to Denver and are seeing an appreciable improvement in our gas mileage for our 2007 Prius. Of note, we also see slightly better mileage in our other car, a Mazda 3. We have been using the 87 octane (mid-range in Denver, but lowest option in Chicago) because that’s what we were used to.

  31. Fuel injectors as opposed to carburators work at high altitude by maintaining an 11 to 1 air/gas ratio (or close to it). It will decrease the amount of fuel as appropriate to the Atmospheric ait pressure. This will decreases the engines power and require more fuel for the same performance. Therefore, it will use a small amount of gas.
    At high altitudes, airplanes weigh less and require less fuel but automobiles maintain the same amount of friction (from the road).
    In cold weather, maintain a full tank (blatter) of gas to keep the blatter expanded AND prevent condensation > water in the fuel tank (blatter).
    Also at higher altitudes than 4000 ft. and in the winter, you can use the lowest octaine (although a medium octaine) and still prevent detonation.

  32. So here’s an even more confusing situation:
    1) I live in Phoenix (low altitude, hot temps) and have consistently been getting between 48 and 53 MPG (just hit 10K mi since buying in April). That said, for the past 1500 miles I’m still getting about 53 MPG, but am only going about 460 miles on a tank before I’m being told that I’m out of gas (as compared to about 550 to a tank before that). However, when I do put gas in, I’m only able to put a little over 9 gallons in (as opposed to a full tank normally of around 11 gallons).
    I took the car in for 10K mi service and asked about this and was told that temperature changes have a “variant” effect on the gas tank bladder. Now it’s only 85 for highs now (as compared to 100s during the summer), but to be told that I’m looking at losing about two gallons of space in my tank and losing about 100 miles per tank (still maintaining the same high gas mileage) seems really strange. Anyone have a similar issue?

  33. I have a Toyota Prius 2007 in Canada, and I found that its actual gas consumption is 5.4L/100km (or 52mile/gallon), which is far above 4.0 to 4.2 L/KM (or lower than 69 to 71 mile/gallon) as they advertised. Who so? Is Toyota misleading its consumers on the mileage?

  34. I was just told yesterday that the reason my Prius is getting in the 30s instead of in the 50s is becasue of reformulated gasoline – would have been nice if I had been told that when I bought the car!

  35. I’ve a 2005 Prius. Almost 76000 miles on it. We have kept track of each tankful from the start. Hit as high as 57 mpg and recently a low as 32 mpg. Had the car in to check on the latter since I’d sen this -low MPG – occurring on the way down to florida from Ohio. In Florida, the auxilairy battery died. OK, 4 years old but I was disappointed. I”ve had 7 yr old batteries. As the battery was dying I saw the little red delta with the Exclamation point warning – Parking Brake something or other. in a situation when the car was on a stable surface.- ie, flat. On the return trip to Ohio, the gas mileage was still in the mid 30’s. Not comparable to previous returns ( 3 times) over the same route / weather/ drivers. (42 to 45 mpg)
    Dealer said there was nothing wrong with the car – computer. I’ll watch and see. New plugs are scheduled- when the dealer gets them in.
    I’ve noticed on this car, as on the others i”ve owned that the brand of gas matters. There are brands I do not use. sunoco, Shell, oddballs, if possible, Marathon. Over the years I’ve seen changes in Shell/Marathon. BP is now OK, Exxon and Mobil are good. In Florida, until the last trip, Race way and Race Track were good.
    Forget Octane. That only controls engine “knock” Has nothing to do with power. In fact, 10% ethanol reduces the power because ethanol has something like 99000 btus and regular gasoline has 126000 BTUs. – translated as driving power.
    Remember the oil companies put oxiginaters in in winter for easier starting. Cuts down on power. They also don’t care if you use more. Witness their profits. Nor do the FEderal gov’t – 18.6 cents per gallon tax and states, anywhere from $.07 to $.30 per gallon tax.
    I know from experience that the car will not get as good a mileage when – with 2 passengr, be loaded to the gills with luggage, painting supplies ( wife) and bags of clothes for the kids from one family to another. But even with the type of driving we do ( 70 mph average) on long trips meaning in excess of 75 mph we had historically made better than 45 mpg. That’s why I’,m concerned over the current mpg. {PS: I have switched from the original come with the car tires ( tire rating 450 to slightly wider tires ( 195 rather than the 185’s) and higher tire pressures – 39 psi front 36 back because the first 2 sets of dealer grade tires wore out in 30000 miles. Typically wear pattern of under inflated. But with 60% front load/40% rear load – driving would put more pressure on the front. New tires are 800-=900 rated tires. Wearing very well.
    Overall, until the recent low PG we’ve liked the car. Very stable, even more so with the new tires, especially in cross winds. Dealers have been helpful. wouldn’t consider the GPS ( disc) system again. came with the car. I ‘d use a garmin or equivalent.
    Good luck ti all with their Prius.

  36. I live in Denver and drive a 2005 Prius. From the beginning I have consistently seen low to mid 50’s in the summer and mid to upper 40’s in the winter. My daily commute is about 20 miles each way. To get 39 an average I’m guessing you would have to take a lot of very short trips.

  37. I have a 2006 Prius. In the start, i was getting 50-54 mgp. Now with the added Ethanol, i only average 30-32 mpg. My driving habits have not change ,so why did i buy a hybrid? My old Corolla got 38 mgp. This was a lesson learned the hard way.

  38. maybe getting a vw TDI diesel with all the torque and fun driving and 40-50mpg average would solve many issues it comes with a turbo and an intercooler so you don’t need to worry about thin air it also drives and corners much nicer.
    I too have a Prius and i hate driving it. its not any better than driving a Toyota echo.
    PS VW is comming with the hibred TDI

  39. I have a 2008 Toyota Prius and live in the San Luis Valley of Colorado. The average altitude in the places I drive is around 8K feet. My mileage does drop considerably in the winter, especially since most of my treks are only about 15 minutes or less. Thus far I have not found a solution to the winter time mileage drop. I am seriously considering turning my Prius into a pluging electric vehicle. With all the tax credits in Colorado and the feds, the out of pocket expense will be small. That way I can minimize the impact of the crummy gas engine.

  40. It doesn’t have anything to do with altitude, it’s the outside temp and the blend of gas you put in which is dependent on the time of year. I have a 2006 Prius and live in Westminster, CO. I get on average about 55 mpg in the summer and about 45 in the winter. Your gas mileage will go down in the winter because the battery operates less efficiently at colder temps. There’s also the “winter blend” of gas that we get. It has a higher level of butane, which burns faster leading to lower gas mileage. Butane has a higher vapor pressure too, combine that with the Prius’s gas bladder which allows for an expandable air gap over the fuel for fuel evaporation, and aggressive driving habits and you can kill your average mileage. Here’s a link to the differences between the seasonal gas blends.
    Hopefully since this was posted a couple of years ago you’ve since figured it all out, and started to get great mileage out of your Prius. They truly are fantastic cars. Hopefully this will help out any future Prius owners who stumble upon this blog like I did!

  41. 2 interesting observations. I just got back from vacation in Colorado driving a 10 year old 4 cyl manual Saturn L series. When driving on the interstate highway, I was driving between 75-80 MPH. I got around 30 MPG at that speed. When I was driving at high altitude(2400 to 3600 meters) with lots of climbing, I got 36 mpg on one tank, and 40 mpg on the other. The car had weak power though (non-turbo).
    The other observation, was that with the lack of power, going up a steep climb, I got passed by a Prius. I am guessing the electric motor adds to the gas engine’s power and allows it to not degrade as much as a normally aspirated gasoline engine does.
    The explanation..”Fuel injectors as opposed to carburators work at high altitude by maintaining an 11 to 1 air/gas ratio (or close to it). It will decrease the amount of fuel as appropriate to the Atmospheric ait pressure. This will decreases the engines power and require more fuel for the same performance. Therefore, it will use a small amount of gas.”
    seems like the best reason for the increased mileage I saw. Maybe along with lower air resistance from less dense air.

  42. Ok, I don’t own a Prius, I have a Honda Fit. When I lived in Colorado and drove up and down the pass to almost 9000′ I was getting an average of 35 mpg. I moved to Texas a month ago and am now only averaging 25 mpg. Help! Anyone know why and whether there is anything I can do? I called the Honda service center and he was clueless.

  43. We have a 2009 Prius. Used it 18 months in and around Fort Collins, CO. Regularly averaged 50 mpg including a few trips each year up Poudre Canyon and to Estes park, and at Interstate speeds (to Denver International airport, Nebraska or Wyoming). Moved to Fairfax, VA in November 2010. Since then we have not not yet achieved more than 48 mpg, usually getting 46-48 mpg. I am disappointed that I no longer average 50. I think the higher elevation helped us get better mpg. Someone has suggested the humidity (markedly higher in VA than in CO) might be a factor. Interesting that our experiences are so varied. This might make a nice research for an aspiring young statistician.

  44. Dave, if it’s altitude, that’s not supposed to happen. It must be a problem with the computer or sensor or something like that. I have driven at high altitudes out west and mileage did not change significantly from what I get in Arkansas, ie, about 48 mpg with my 2006 Prius.
    But I just finished driving to Colorado and back for skiing and the mileage dropped to 37-38 even before we got our of Arkansas. It stayed that way all the way to Colorado, no warning lights ON. The Toyota dealer I talked to in Denver said it could be a 100 things but there was nothing they could do if the check engine light was not on. The only thing *I* could do was fill up with high octane gas (90). When I did, the mileage immediately went up to normal. As long as I kept using premium, the mileage stayed up. On the drive home, I tried mid-range octane and guess what? Mileage dropped to midrange between premium and “unleaded.” I am clearly getting mileage in proportion to octane. Which should not be. I suspect something like a computer malfunction but have not yet taken it to the local dealer.

  45. I live at 10 feet above sea level. I have a 2007 Prius. I just had a tune up (had the air filter changed, and got new spark plugs); have low rolling tires. My current MPG is 29 local driving; long distance about 40. Before the tune up and new air filter, my mpg around town was 34 and my long distance about 50. I drive the speed limit, and don’t do “jack rabbit” starts. At mid night tonight I’m, going to be at the same place I would be anyway, so why be in a rush. I use Chevron (and Texaco) gas. I think Chevron bought Texaco out as they both use Techron in the gas. There are a few places around here I could get the “real regular gas”–no ethonol, but of course it cost more. I would like to know if I went to non ethonol gas how many mpg would it increase, if any. Has anybody tried it? To make it worthwhile, you would have to gain 20mpg or more. I used Premimum (ehonol) one time and it made no difference in my mpg. What experience have other people had?

  46. I was getting lifetime average of 48.2 mpg on my 2006 Prius. I just got a tune-up, new 12 volt battery & tire rotation. With the battery change, my lifetime mpg was reset. Now I am getting 26-33 mpg. Cold here in WI but nothing new. I routinely turn off my heat to facilitate mpg in winter. I have not changed my driving habits and tires are inflated. Any ideas as to why the HUGE drop in mpg?

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