Prius MPG
I thought I’d ramble a bit on Prius mileage. I have a 2005 model (called the Prius II by some). I have been using the built-in mileage computer to track my tanks. I like to be above 50 mpg when I go for my next fill-up, and manage that the majority of the time.
I’ve been playing a new game though, which is to reset the computer each day that I drive. Prius owners know, but perhaps other folks don’t, that the Prius mpg is a little complicated. There is a computer controlling when the gasoline engine is turned on, and when the electric motor is used (or charged). One obvious decision the computer makes is to run the engine for a while when you first start out – just to warm everything up. The engine has to be warm for its own health, and the catalytic converter has to be hot to do its job.
So I find that I get about 20 mpg in the first mile out from my house, about 30 by the second mile, and then it climbs according to the traffic and speed mix. The most brutal thing I can do is a 1.5 mile drive to breakfast, and then a 1.0 mile drive to the market, and then a 1.5 mile drive home. The worst I’ve done is to get 35.6 mpg over an 8 mile “day out.” On the other hand, if I go any distance (25, 30, 40 mile days) I do get home with better than 50 mpg.
On top of all the other factors, maybe this is a reason, that if you are really going to do low mile days, to get an efficient non-hybrid. You aren’t really going to see it shine unless you run it farther once it has warmed up.
(I haven’t been typing much because I crashed my mountain bike and got 7 stitches in my left pinky. Feeling better now, and stitches come out Tuesday.)
May 7th, 2006 at 6:32 pm
Hope you and the bike wind up fully repaired soon.
I finished reading “A Thousand Barrels A Second” but I forgot to make detailed notes. I’ve got to go through it again now. Oh, the horror. ;-)
May 8th, 2006 at 3:24 am
I hope you found it useful. Did you like the ending?
May 8th, 2006 at 10:03 am
We see similar results – except we’re lucky to end above 50, since the vast majority of our trips are sub-mile. The problem with the conclusion, though, is that it apparently rests on the theory that non-hybrid cars don’t suffer a large warm-up penalty themselves (but they do – we just don’t know how much proportional difference there is).
IE, when I drove my wife’s old Civic hatchback, had I had a fuel readout, I might have noticed that although my “tank mileage” was 38 at its peak, that meant that the one-mile trip to the highway was 20 mpg and the remaining 9 highway miles to work were 40 mpg. (Maybe the city mileage would have improved to 30 or 35 for the second mile, too).
Everybody claims that gas engines do better after being warmed up, but relatively few have the on-screen readout to actually tell you how MUCH better. I’m sure the Prius’ gap is larger than most, but I’m also sure I get better mileage on that one-mile grocery run than I did in the tiny Civic Hatch.
May 8th, 2006 at 10:28 am
My Vespa gets consistent 50mpg, and almost all my trips are under a mile.
May 8th, 2006 at 11:01 am
Yeah, I know M1EK, lots of assumptions in this ramble. Maybe someone with a conventional car and a trip computer will fill in some details.
Aleks, I can’t believe you because the Vespa doesn’t have a computer! (juat kidding, i like scooters too).
May 8th, 2006 at 12:34 pm
Aleks,
I like scooters too, but you ought to recognize that moving a Vespa (up to 45 or whatever your max effective speed is) and moving a car the size of the Prius, and effectively getting the same mileage, says a lot about how much ass the Prius has kicked.
May 8th, 2006 at 12:53 pm
Gasoline engines pay a fuel economy penalty when cold, but apparently not to the same extent. My car’s computer readout shows maybe a 15% penalty over the first five miles, with most of the damage done in the first mile.
May 8th, 2006 at 12:58 pm
After 15 months with a Prius, I’m convinced that trip length is THE single most important factor in mpg – much more meaningful than the traditional city/highway breakdown. It’s no great feat to average 50 mpg in a Prius if you drive it for 30 minutes at a time, whether it’s in slow-and-go traffic or on the highway. But, as you say, getting 50 mpg on the first 5 minutes of the day is well-nigh impossible.
May 8th, 2006 at 1:21 pm
Seems like these sub-mile trips are where a plug-in hybrid would shine–then the gas engine wouldn’t have to be started at all. Of course, it might help if there were a way to inform the car in advance that the trip would be short.
May 8th, 2006 at 3:02 pm
It almost seems to me that a software change, even without the plug-in, would improve things. Let the car go for a ways, at low speed, and only start up when you really need it …
but then maybe they’ve already thought of that, and want the engine to be warm before you try to hit any real speed. for me, as i go slowly 1/2 mile through my condominium complex, i’m wasting gas … but on average maybe it’s a good bet.
i’m a special case anyway, as i live at the bottom of a hill and have to climb out every morning. on the other hand, i get to do the last 1/2 mile (if the engine has warmed up on a long trip) battery only.
May 8th, 2006 at 3:06 pm
Re ATBAS, I think the ending was unrealistically optimistic. If we can pull off anything that good, I’ll be ecstatic.
May 8th, 2006 at 4:40 pm
;-), yeah. my interpretation was that Tertzakian was trying to thow a chaser of hope after all the previous gloom …
May 8th, 2006 at 7:07 pm
Makes me wonder what effect a block heater would have, on a timer.. set an hour or something before departure….weather would factor in too. This would go for any car I suppose. Probably some benefits in lowering pollution too.
May 9th, 2006 at 4:56 am
Pretty much concur with your comments on Prius mileage (and ‘regular’ cars) being less during warm up. One thing I’ve discovered is that the computer calculated mileage isn’t necessarily accurate. Ours fairly consistently overstates the MPG by about 5% – I do the math at every fill-up. To get great insight into the parameters that affect mileage, look here: http://privatenrg.com/ For a look at the maximum potential of pulse and glide driving, look here: http://hybridcars.about.com/od/news/a/100mpgrecord.htm
Regarding electric only mode on demand for short trips – my understanding is that Toyota includes a switch to provide this in Japan & Europe, but not to us dumb Americans. Not sure why. I’ve read on-line about DIYers installing an aftermarket switch. Bottom line is if you drive pulse and glide as much as possible (traffic dependent), we find that the mid-50’s are well possible. Ambient temp has a big impact. We averaged 52 last summer, 53 in the fall, 48 through the winter, 53 early this spring, getting 55+ the last couple of tanks, as P&G becomes more internalized, and as the weather warms – at least until AC is needed (we’re in NC).
May 9th, 2006 at 5:33 am
I’ve just got an Echo, so I don’t get a fancy computer to do the calculations for me, and I only know my mileage over a much broader time period. But I note that if I run some errands on the weekend, trips to the library and more separate trips than I would like to admit to, this hardly hurts my gas mileage. What takes me from a 19.5kpl (46 mpg) fill up to a 17 kpl (40 mpg) are when I lose my zen multiple times commuting to/from work. It’s an echo; it’s not meant to speed around someone. When I keep my zen, I get amazing (to me) mileage. When I lose my zen, I just get good mileage.
May 9th, 2006 at 7:12 am
I have a 2003 Prius with about 54K miles on it. I have made many long trips in it, coast-to-coast, in winter (ice, snow) and summer (100F on Gulf Coast), and at 11500 feet in the Rockies. It is a good solid machine, well designed and well built. It has not yet had any mechanical work. The one place where Toyota engineers made a mistake was in the choice of the OEM tires, which have a life of only about 30K miles.
The 2001-2003 Prius model has the same warmup low-mpg problem that the 2004+ Prius has, but even more significant, because it does not have the hot water thermos bottle that the 3rd-generation[1] Prius has. My Prius takes about 10min to fully warm up. I live in a small city, and can drive to the other side of town in less than 10min, so I typically get 30-35mpg around town, compared to 40-45mpg on the highway under good conditions.
Why is this? I am fairly sure that it is due to a policy decision by Toyota management. They decided that their highest priority was low emissions, and gave that order to the engineers. As a result, the software runs the engine with a rich mixture at cold start so that the catalytic converter will have to burn up the excess fuel and will reach full operating temperature as quickly as possible. If highest possible MPG had been the goal, the car would emit additional hydrocarbons while the converter is warming more slowly, but would still be a very clean car. Because I live in a small city, I wish that Toyota would offer a replacement chip with different software to implement a Max-MPG policy instead of a Minimum-Emissions policy.
-Don
[1] Re ‘3rd-gen’: many Prius owners do not know that Toyota sold their 1st-gen Prius model only in Japan during 1997-2000; although the 2004-2006 Prius may be called version ‘II’, it is really the 3rd generation. Toyota has 10yr of production experience with hybrid technology, with three whole design cycles, and a fourth cycle almost ready, while some US manufacturers have *zero* production experience. Sigh…
May 9th, 2006 at 6:20 pm
coffee17: I think lots of people could use a more Zen approach to driving. I frequently see people in large SUV’s who respond to a red light ahead by accelerating toward the stopped traffic ahead, even as I’m in neutral coasting along. They get to come to a full stop, whereas I may achieve Nirvana by coasting just to the proper following distance of the car ahead as it achieves my speed.
My Zen coasting is often ruined by people who cut in, fail to pay attention and move when the traffic ahead moves, or (worst) both.
May 10th, 2006 at 1:20 am
I’m curious how many barrels of oil were used to produce the Prius. It seems to be a false economy on so many points, and completely sours me to the whole hybrid concept.
Fundamental physics tells me it is impossible to convert thermal energy to kinetic energy to electrical energy and back to kinetic energy without significant losses at each transition. While regenerative braking does recoup some of those losses, it still doesn’t make sense from a pure physics perspective. We’re still throwing away 2/3 the fuel’s potential to the cooling system and the exhaust at the very first phase.
It seems some of the thermodynamics of internal combustion engines are missing in this discussion. Yes, a block heater would improve the start up efficiency, but the energy used to heat the block would have to be recovered. Does this exceed the losses experienced by cold cycle running? Only Toyota knows. Maybe they missed on this one?
Any internal combustion engine has to reach thermal balance (full operating temperature) in the cylinder head(s) and piston(s) before it will operate at peak efficiency. Until the materials are fully heat soaked, energy from the combustion process is being diverted from driving the piston into heating the head(s) and piston(s). Again, it’s fundamental physics of our current engine technology. This is the cause of the poor mileage you’ve all noted.
If Toyota truly had efficiency in mind, the Prius would have a Miller Cycle diesel, not a gasoline powered engine. Large diesel ship engines run at 50%+ thermal efficiency, a far cry from the best gasoline engines, and a similar deployment in an automobile, if optimised for operation in a narrow range of rpm, would yield similar efficiencies. Why didn’t they do this? Unacceptable noise? Particulate emissions? Consumer resistance?
I am still trying to grasp the whole battery production and recycling effort and the energy costs surrounding it. Mining the metals, refining the metals, producing all the plastics (from petroleum stocks), dealing with the toxic elements, and finally who pays the bill to recycle the thing when it is used up? While it only makes sense to recycle the batteries, there is a cost associated with this activity, both monetary and human. The metals in the batteries are highly toxic, and so are the reagents. Eventually the Chinese will no longer tolerate their factory’s abominable environmental conditions. At what cost will these batteries be recycled? How many more barrels of oil to reuse the materials and sufficiently protect the workers while they perform their task?
The pro-hybrid arguments remind me of the nuclear energy arguments when I was younger. Nothing could produce electricity as cheaply as nuclear power, and Westinghouse had the numbers to prove it. Except, they never factored the real disposal cost into the total cost of generation. They figured by the time the intial batch of reactors started dying off, they’d have new technology, and breeder reactors would be common to make sure the fuel waste didn’t become too great a burden. We know how well that strategy worked now.
I can only imagine a future with more false economies pushed on us by marketing geniuses, until we really do run out of economically sensible energy.
May 10th, 2006 at 3:19 am
there are competing numbers being thrown around for total lifecycle energy in a prius. that’s sad, but i guess it is human, as it becomes another area of marketing and contention.
while i look forward to good numbers, i don’t really see a motor/generator and a battery pack as a tremendously large increased energy expense over the car itself. especially not when averaged over a 200K mile toyota life.
as far as other technologies, i welcome them. i bought the prius because it was the best i could get in california, in 2005. if any other automakers can beat that (and california will legaliize them) more power to them.
May 10th, 2006 at 8:49 am
Toyota could not get permission
To use the compression ignition
The problem is real
Diesel’s Achilles’ Heel
is pollutants; it goes to perdition.
May 10th, 2006 at 9:29 am
:-)
May 10th, 2006 at 2:18 pm
Well said. I guess the Europeans have embraced diesel particulates as not so important to their overall air quality.
June 2nd, 2006 at 9:59 am
In response to Don in VA. I can tell you’re not an automotive technician, or engineer. Transient Analysis is the phrase we use to determine the correct air/fuel calibration required for cold start drivability. Toyota doesn’t aimlessly waste engineering resources on frivolous requirements, just to irritate customers. The Prius is no different in having to meet the same stringent U. S. standards required by all other vehicles in its class. The next time one is irritated with their hybrid cold start characteristics, try starting a small engine with the choke off and let me know how that works out for you? Secondly, if an engine were to dump raw hydrocarbons on a catalyst brick as mentioned, it will soon melt down like Chernobyl’s reactor and someone will be visiting the repair shop. R.D. Dearborn, MI
August 15th, 2006 at 12:52 am
re Push Button Prius:
- apparently the problem in the US is regulatory, to with the calculation of emissions. Hence no ‘electric only’ setting
- what Toyota has yet to introduce is a Prius that ‘plugs in’– there is a hack to do this, but (to me) it is unclear why you cannot plug in your Prius at a power point
(those who live in places like Alberta and Minnesota will know that every parking garage has plug in points for the engine block heater– the infrastructure exists)
A related problem here in the UK is that you can’t legally string a power cord from your house to your car on the street. Here in London, where all-electric cars are mushrooming, this is a real problem: most people don’t have car garages at home, and park on the street.
These simple regulatory barriers are as much an obstacle to adoption as any technology issue.
On diesel, once clean diesel is availabe (2008 EPA mandate) diesel cars will be feasible in the US. Given the quality issues with the 1970s GM diesel cars, plus the absence of universal filling infrastructure, it remains to be seen how popular they will be.
Here in Western Europe about half of new cars sold are diesel (aggregating across countries).