During the late summer of 2019, I purchased a 2014 Prius V Three. First and far most, it was purchased for the economy with a rating of 40/45. And, in that I am nearly seventy-six inches in height, it is roomy, the perfect sized compact for a "bigger" than normal person. I leave the fuel efficiency display set on "range". When the car was first purchased, this always registered well-over 450 miles per full-tank of gasoline. After a few months, this was only registering about 375 when filling up. I had been by a local dealer for regular oil services and used the synthetic blend that Toyota recommends. The dealer has recommended a tune-up in less than 10K, but it seem that this range loss was rather drastic. And, I was hoping that it could be improved without spending $500.00 for a tune-up anytime the fuel efficiency drops. In that I am very frugal, I was purchasing the "best" priced fuel in town from a smaller national chain which is known for its "well-priced" gasoline. This filling station was consistently between a nickel and a dime less than the average for a gallon in the city. And, what was best, a station is only about five blocks from my home. However, I found that I was getting what I paid for. I thought that the problem could be the quality of the fuel that I was buying. So, I tried another national chain, that is somewhat larger and offers a "guarantee" on their gasoline. But, it is a mile or so from home. I did not feel that they would reimburse me if the fuel efficiency kept declining, but thought that they must have a pretty good product if they stand behind their gasoline with a warranty covering any engine damage done by "bad gas". This is the third fill-up at that station and the range now reads nearly "400" versus "375" on a fill-up. This was not instantaneous. The first fill-up with half a tank of the new fuel and half of the old produced "378" on the gauge when it first registered. The next one produced "384". And, the last one read "396". The last couple of fill-ups were mostly the "quality" fuel and occurred when about "50" miles were left on the range gauge. I am not much for on-line forums and "web-chatting", but I went searching on-line for a potential simple solution when the range of my Prius V Three started dropping. I found this PriusChat. So, when I sorted out this one potential solution, I thought that I would share it for other owners. NuevoArchitect SIDE NOTE (on future fuel efficiency): I have taught computing part-time at colleges and universities since 1999. I have a pair of post-baccalaureates. One is in computer science and the other is in software engineering. I have a mixture of STEM skills and started out as a physics major in the late-1980s at Vanderbilt University as a NCAA Division-I student-athlete. Some records that I have from Vanderbilt stated that I scored among the top-50 high-school students in the country on the 1988 Advanced Placement physics exam. In other words, I am "book-smart". Women, especially, and humans, in general, leave me rather confused. Algorithms and equations are my friends. These are highly predictable, disciplined, and regimented. My original goals upon leaving high school were earning a doctorate in physics and studying energy efficiency models. I was hoping that I could help this world end its dependence on fossil fuels. The academics were quite manageable. But, life's situations derailed me, and I ended up pursuing computing. Making this protracted story as short as possible. I am a "non-traditional" researcher who works in scientific theory since it only requires a paper, pencil, and possibly a computer. Grant funding is not needed, and I freely disseminate the valuable ideas which arise. While studying at Vanderbilt, one of my professors mentioned the Carnot cycle which describes heat engines during a lecture on thermodynamics. He said that Carnot's theory predicts that nearly seventy-percent of the energy in a tank of fuel is lost through the radiator of an internal combustion engine. Within the past couple of decades, I have written automotive manufacturers asking if they could design an engine which recovers a significant portion of this lost "heat" energy. I am not sure if this is feasible. I do not have a background in automotive engineering; I only have a couple of years of college physics and its theories. I am just sharing this idea. If the "energy" conscious portion of the automotive community starts a "letter-writing" campaign requesting such a future engine enhancement, it might materialize if it is feasible. The (ORNL) Oak Ridge National Laboratories in Tennessee is responsible for leading the national research effort in energy efficiency.
Summer vs. Winter gasoline formulation. Just a WAG as your profile omits your location. Welcome to Prius Chat.
For starters: Why Mileage Gets Worse in the Winter | PriusChat Efficiency improvements have been a very big deal for a very long time, with tons of research happening since essentially forever. And with considerable success so far, and numerous visible paths forward. I'm not sure how this proposed letter writing campaign would help. Rather, consumers should vote with their wallets among the many higher efficiency choices already on the market. Not just on motor vehicles, but also on home appliances and climate control too.
Too much irrelevant information in the original post. There are a TON of possible causes for a reduction in gas mileage. Driving habits is right up there near the top. BUT......like the "ratings", the Distance to Empty is just an estimate and isn't intended to be terribly accurate. If you really want to track your fuel usage, you MUST record the miles traveled and the fuel used over multiple fill ups and do the math. A small difference from one tankful to the next is to be expected. Even a large difference occasionally is not necessarily an indication of a problem........if the nozzle shuts off early for example.
I believe what your prof was describing was thermal efficiency. The 75% waste heat is partly lost as exhaust gasses and partly lost in cooling the engine. The Prius uses an Atkinson cycle engine rather than the typical Otto cycle. The Prius engine approaches a 40% thermal efficiency so only 60% of the thermal energy is lost. A standard Otto cycle engine draws in one cylinder volume of air/fuel, both valves close and then the piston compresses it. As the piston reaches the top of the cylinder, the mixture is ignited. The burning fuel/air pushes the piston down during the power stroke. The piston then moves back up during the exhaust stroke and pushes the hot gasses out of the cylinder. There is still a lot of energy left in the expanded hot gasses when the piston reaches the top of the exhaust stroke. The remaining hot gasses are pushed out through the the exhaust system. This cycle results in optimum power but at a lower thermal efficiency. An atkinson cycle draws in one cylinder volume of air/fuel but the intake valve remains open for about 25% of the compression stroke. The piston traveling upward on it's compression stroke pushes some of the fuel/air mixture back into the intake manifold. The intake valve eventually closes and as the piston reaches the top of the cylinder the smaller fuel/air is ignited. The burning fuel/air pushes the piston down as it expands during the power stroke but due to the smaller fuel/air charge, there is less excess heat/pressure to be vented at the end of the exhaust stroke so the engine is more efficient. This cycle uses less fuel, results in less power but yields higher thermal efficiency. For a hybrid, optimum power is not as important as efficiency since it's engine shares propulsion duties with an electric motor. Hope this helps.
If you think back to the thermodynamics section of whichever physics sequence you took, that's exactly it. A heat engine is an ideal engine that turns heat energy into work, and a Carnot engine is a particular type of heat engine first proposed by Nicolas Carnot in 1824--one consisting of four phases, two isothermal and two adiabatic. The efficiency of a Carnot engine is equal to 1 - (low temperature)/(high temperature). But...that is an ideal engine; it depends on such unrealistic assumptions as the existence of a perfect insulator. Real engines are much more complex. Writing to automotive manufacturers to ask them to make their engines more efficient strikes me as redundant. This is exactly what they've been trying to do--and paying armies of engineers to do--over the last several decades.
