First Prius highway trip, horrible MPG

Discussion in 'Fuel Economy' started by swineone, May 16, 2015.

  1. swineone

    swineone Well-Known Member

    Hello everyone,

    Today I took our Prius to the highway for the first time, and I have to report that I'm highly disappointed in its MPG.

    It was a 62 mile trip, with at most 10 of these miles driving in the city. According to the display that shows in place of the HSI when the car was turned off, trip time was 1h39min, although I estimate I spent somewhere around 20-25 minutes in city driving conditions. Hence I estimate my average speed was 42 mph or so -- it was nearly midnight and the road was as close to empty as they come so it was perfectly safe to drive that slowly. Again according to the end of trip display, trip fuel consumption was 3.9 l/100 km which works out to about 60 mpg. This was a deep disappointment for me -- before leaving I was pretty sure 70 mpg was guaranteed with these driving conditions, and my honest expectation was 80 mpg or more.

    For context, outside temperature was 18ºC (64ºF), all windows were closed, and no air conditioning/heating (only sporadically and just for a few seconds each time for defogging the windshield). Since the trip was fairly short, it's worth noting that the car was semi-warm at the start of the trip -- it went into Stage 4 after driving less than a mile. Tires were at 40 psi front/36 psi rear, just had them pumped yesterday. Cargo weight was about 500 pounds (myself, my wife and a bit of luggage). For instrumentation I have an OBD-II WiFi dongle with the EngineLink app for iPhone. I was mostly monitoring RPM. Driving technique was pulse and warp stealth, trying to keep the pulses within the ECO area (1400 RPM-1800 RPM), only rarely going up to 2200-2400 RPM at the steepest inclines. When EV mode was available I tried avoiding it. Also, when going down hills, rather than regen braking I just let the car coast in warp stealth mode, even sometimes exceeding the speed limit (to avoid the losses associated with conversion to electrical energy). In short, I think I went by the hypermiling book and was frankly expecting much better mileage. I just have no idea what I could have done better here.

    For the return trip I will just set the cruise control at the same 42 mph (conditions permitting) and will see how it does, just in case there's something seriously wrong with my driving technique.

    My best hypothesis for the crappy mileage is the sorry excuse for fuel that is available here in Brazil: regular gas with 27% ethanol content. Going purely by energy content, it's about 10% less than pure gas, but still, that'd mean someone doing the same trip, at the same speeds, using the same technique, would be getting 66 mpg or so -- whereas, from what I've read here, under the driving conditions outlined above, something like 90 mpg should be doable, if not even more. I'm pretty sure the ECU maps are pretty screwed up due to the insane amount of ethanol in our fuel, burning fuel in a way that's much less efficient than the 10% energy content difference would suggest. Either that or there's something seriously wrong with my car.

    I intend to let this tank drop to nearly empty and then fill up with premium gas for the next few tanks to see if it makes any difference. I'm aware it shouldn't, yet maybe the fact that our premium gas has "only" 25% ethanol, versus 27% ethanol in regular gas, might help a little bit.

    I appreciate any thoughts, suggestions or hypotheses anyone may have regarding this situation.
  2. EdwinTheMagnificent

    EdwinTheMagnificent Legend In His Mind

    And I've been moaning about our 10% ethanol content ! At 55 MPH , and driving with load , in 65 deg F temps , I can get about 60MPG highway on our E10. But I've never actually re-set a trip-meter after getting up to highway speeds. For instance , my commute to work is about 7.5 miles suburban roads , 23 miles of highway , and another 3.5 miles of suburban roads. Today it was 66.9 MPG. The real enemy here is the government ( yours AND ours ) who have determined ( in their infinite wisdom) that ethanol is a good fuel for motor vehicles.
  3. brick

    brick Answers to "that guy."

    Brazil doesn't do ethanol the same way the US does it. Their use of sugar cane is much more efficient than our use of corn. Despite the apparent FE disadvantage it makes some sense as a transportation fuel.

    On the original question, 60mpg seems like a reasonable result for that kind of trip. Crazy high Prius numbers come from lower speed P&G cycles.
  4. swineone

    swineone Well-Known Member

    Well I won't go into a lengthy tirade here about ethanol, but I will say this: the vast majority of new cars here are flex fuel and have been so for the most of the last 10 years or so; in fact it's getting harder and harder to find a decent, non-flex-fuel car (and they'll have my lifeless head on a platter before I buy one of these pieces of crap, who all have truly awful mileage -- I've always made a point of buying gasoline-only cars).

    The point is, there's no shortage of flex fuel vehicles on the roads to use ethanol if it made economic sense. Never mind that there's a significant chunk of people are not literate enough to do the math and decide between gasoline and ethanol taking into account the lower energy content of the latter, they might just go for ethanol all the time because the price/liter is cheaper, regardless of the awful MPG. Yet the government finds itself compelled to raise the amount of ethanol in gasoline all the time in order to help the ethanol business, forcing this awful excuse for a fuel down our throats.

    In fact, until recently, by law the maximum ethanol content in gasoline was supposed to be 25%, but they actually went in and changed the law to allow 27%. This entailed a bunch of tests on cars to make sure the engines wouldn't blow up with it. These tests were only done with regular gasoline and not premium, which then stayed with "only" 25% ethanol content. In the end, as I recall, the government went ahead with 27% but recommends that all owners of gasoline-only cars fill up with premium fuel, at our expense of course, because premium kept at 25% ethanol content (now of course that's BS, everyone kept using regular gas as usual, although if anything does happen to the engine, they're screwed). In other words, the new gasoline with 27% ethanol is meant for use only in flex fuel vehicles where you could mix any amount of gasoline with any amount of ethanol anyway, no need for government regulations punishing owners of gasoline-only vehicles. This is such a load of BS and it raises my blood pressure so much that I will cut this already too long tirade short.

    Back to the subject, I may have been mistaken about the expected MPG in this situation, but still, I was thinking of the following graph taken from PriusChat user bwilson4web:


    Looks like somewhere between 75-80 mpg should be doable, again with pure gas, no? I recall reading on Hobbit's web site that a rule of thumb for Prius highway driving is 60 mpg @ 60 mph, although you could do better with proper techniques, yet here I am getting 60 mpg @ 42 mph.

    I just wanted to make really sure there's nothing wrong with my technique or my car (well nothing that I have control over, considering the ethanol content in the gasoline).
  5. I'd pump up the tires a lot more (depending on max psi on sidewall)
  6. ALS

    ALS Super Moderator Staff Member

    It's that 27% ethanol blend that killed your fuel mileage. I would be thrilled with 60 mpg U.S. with that weasel piss gas in my tank.

    If you had U.S. 10% ethanol content in the tank I would have expected 3.6L to maybe 3.7 at worse per 100 km or 63 to 65 mpg U.S..

    Pure gasoline, no ethanol at all 3.35 L/per 100 Km or 70 mpg U.S. could have been done on that trip.

    Even at 10% ethanol I lose anywhere between 8% and 10% in fuel mileage in both my cars over straight gas.
  7. EdwinTheMagnificent

    EdwinTheMagnificent Legend In His Mind

    Sounded like a lengthy tirade to me. :)

    The Stepchild is right. More air. At least up to the sidewall max.

    Hobbit's rule of thumb was based on a Gen 2 Prius 1.5 L engine , I believe.

    Weasel piss ! That's a good one. I usually just call it "corn squeezin's".
  8. swineone

    swineone Well-Known Member

    Well I did try 42 psi front/38 psi rear in my tires, but the car felt like a go-kart with no suspension. You just can't overestimate how crappy Brazilian roads are. I'm afraid this might even mean an early suspension job for this car. 40 psi front/36 psi rear feels like a good tradeoff between fuel economy and comfort.
  9. I spent 6 weeks there. Got to drive around Sao Paulo in a car and motor cycle. About went to jail too because the police had never seen an international drivers license and I don't speak Portuguese. Haha. Oops
  10. Mendel Leisk

    Mendel Leisk 2010 Prius (CAN Touring) Staff Member

    What year is your Prius? Is it the LXL? Or?

    If you look at Prius fuel economy ratings, it gets better mileage around town, lower speeds.
  11. 08EscapeHybrid

    08EscapeHybrid Moderator

    That mileage seems reasonable to me considering the high ethanol content.
  12. swineone

    swineone Well-Known Member

    My Prius is the 2013 model year. As for the trim level, no idea -- apparently it's sold in a single trim level over here, and I'd wager it's the simplest one available, or at most the next.

    I'm aware the Prius really shines in city not highway driving, but still, my highway driving scenario is rather low speed. Driving under the same conditions with my old Fit, I could easily get the same 60 mpg, and with some effort, even 70 mpg. I was just expecting more from the Prius, but since everyone else is telling me this isn't far from what I should expect, then that's that. I'll just see how the car does tomorrow under cruise control, to make sure there's nothing wrong with my technique.
  13. 08EscapeHybrid

    08EscapeHybrid Moderator

    The Fit is a smaller, lighter car, and its setup better for highway. The Prius is made to shine in low speed city traffic. You can pull impressive highway numbers in a Prius, but it requires some aggressive hypermiling techniques.
  14. EdwinTheMagnificent

    EdwinTheMagnificent Legend In His Mind

    Today , 67.4 MPG , but my 34.5 mile commute does have about eleven miles of non-highway suburban roads. For me , maybe 60MPG on the highway(so far).
  15. swineone

    swineone Well-Known Member

    So I made the return trip yesterday using cruise control, set at 50 mph -- a bit above my calculated speed in the initial post, but trip time as measured by the trip computer was basically the same, so I guess the actual average speed on the highway was 50 mph indeed. This time a little A/C was needed, but also, it was a daytime trip so headlights were off. All in all both trips should be fairly comparable. The result with cruise control was 4.5 l/100 km (52 mpg), in fact a bit better than I was expecting (I would have guessed closer to 5.0 l/100 km or 47 mpg).

    So, while I did beat cruise control, it wasn't by a considerable margin. I conclude that my technique could use some improvement. Part of it, I guess, is a lack of discipline for keeping speeds near the trip average -- I should stick to a specific starting and ending speed for my P&G cycle, only making allowances for the terrain. I'll try this next time and see if things improve.

    Anyway, thanks everyone for helping out.
  16. EdwinTheMagnificent

    EdwinTheMagnificent Legend In His Mind

    swineone , you are doing remarkably well for the E27 swill , I mean fuel , you are forced to use. I'm still not sure how the Fit was able to be so efficient on that fuel.
  17. ALS

    ALS Super Moderator Staff Member

    I have no idea the terrain you're driving through but if it was repetitively flat at 50 mph that is terrible fuel mileage for a Prius even with your high ethanol content. At 65 mph with cruise control and AC, I average around 52-53 miles per gallon or 4.4 - 4.5 liters per 100 KM. That is crossing from the western part of Pennsylvania to Philadelphia and back including some hilly terrain along the way. At 50 mph I would easily be north of 60 mpg with 10% ethanol fuel, cruise control and AC on.

    Even with E-85 I would expect to see at least 4.4 -4.5l per 100 km at 50 mph.

    Try a few tanks of gas with a high quality fuel cleaner. If your Toyota dealer or other car dealers in the area carry BG products run a can or two of their K44 through the fuel system. The BG K44 is the best fuel system cleaner I have found in my travels.

    As far as over the counter at your local auto parts store goes, Techron Concentrate Plus is the best.
  18. swineone

    swineone Well-Known Member

    Finally someone agrees with me this is awful mileage. The terrain on this trip is very hilly, in fact at one point during the trip (with cruise control) the battery fully charged to 80% SoC and cruise control engaged B mode automatically. One day I will try to find a long stretch of flat road, reset the trip counter and engage cruise control to see what kind of mileage I can get.

    Are you sure 4.5 l/100 km at 50 mph is doable with E85? The back-of-napkin calculation everyone with flex fuel cars does here, when comparing the cost of E100 and gasohol at the pump, is that mileage is 30% worse on E100 compared to gasohol.

    In fact I just had a look at our the Brazilian equivalent of EPA mileage for 2015 model year cars, tested using the same EPA highway cycle as the US, and the very best fuel ethanol highway fuel consumption, across every single car tested, is 9.35 l/100 km (the same car gets 6.33 l/100 km with gasohol) -- and that's a small car, probably less than 1 ton, with a 1.0l engine. Sure none of these are hybrids, but still, I find these E85 figures wildly optimistic.

    Neither of the products you suggested is available here, but I'll have a look at what fuel system cleaners are available, and I will try one of these.
  19. ALS

    ALS Super Moderator Staff Member

    You're probably right on the E85. I was going by the fake numbers the Gov. uses, saying you should get 85% of pure gas. Hilly terrain will also hurt your mileage pretty severely.
  20. phoebeisis

    phoebeisis Well-Known Member

    Once you are at recommended tire pressure
    More tire pressure won't give a big RETURNS
    I forget the exact numbers-but the difference between 36 psi and 46 psi-is maybe 1.5% better FE- maybe 1 mpg better
    But on crummy roads-New Orleans and Brazil apparently-
    You will lose your fillings

    60 mpg 27% and 42 mph-some slowing since 10 miles were city-
    is ABOUT RIGHT- as others said
    Our 2006 gets about 53-55 mpg at 60-65 mph- 10% ethanol

Share This Page