Toyota Prius vs Jeep Patriot Comparison is Deeply Flawed
by Michael Graham Richard, Gatineau, Canada on 06.12.08
The Old Hybrid vs. Diesel Debate
It's very hard to be completely scientific when doing real-world car tests. There are lots of variables to keep track of, and gathering enough data can take a while (just one drive leaves a big margin of error). But still, if taken with a grain of salt, these tests are generally useful.
But once in a while, you find such a test that has gotten something very wrong, enough to put the whole conclusion in doubt. It's the case with "Toyota Prius vs Jeep Patriot: the great MPG test by Claire Edwards and Jay Nagley" by Clean Green Cars. What were their conclusions and why do we think they're wrong? Read on.
Results of the Toyota Prius Hybrid vs. Jeep Patriot Diesel
The idea is simple: Get the best-selling hybrid car in the world and a SUV that recently was acclaimed for its good fuel economy, and see how they stack up against each other. Right from the start there's a temptation (conscious or not) for journalists to do things in such a way that the final result is counter-intuitive. That helps attract readers and makes for a more punchy article. We can't know if that was a factor here, but Claire Edwards and Jay Nagley (the writers) seem to have done a good job of making the test fair. They drove in both the city and on the highway, they followed speed limits and swapped car in the middle of the test to compensate for driving styles.
Toyota Prius vs. Jeep Patriot: Test Results
So what were the test's results? Well, after 160 miles, the final numbers on the onboard computers were 57 MPG for the Prius and 42 MPG for the Jeep. These are imperial gallons since they are in the UK. In US gallons, that's 47.4 MPG and 34.9 MPG respectively.
But then they went to fill up both cars to see how many gallons that would take so they could re-calculate the MPG numbers to make sure that the onboard computers were not too far off. The numbers they got were very different from the firsts: 38.9 MPG (32.3 MPG US) for the Jeep and 39.9 MPG (33.2 MPG US) for the Prius.
That makes them conclude that the onboard computer of the Prius was 17.1 MPG off, and that the Jeep's numbers were only 3.1 MPG off, and that both vehicles almost burned the same amount of fuel during the test.
Toyota Prius vs. Jeep Patriot: Why is the Test Flawed?
Reddit commenter nomopongo beat us to the punch, so we'll just quote him/her here: "The Prius does not use a conventional fuel tank, and because of this, you can't use the refueling numbers in order to calculate MPG, unless you do it over many fill ups. The Prius uses a resin gas bladder in order to minimize fume-related pollution. The article is wrong."
The Prius hybrid indeed uses a laminated resin fuel bladder inside its gas tank to reduce the amount of gasoline fumes that escape, thus reducing air pollution. Nominally, the gas tank of the Prius can contain 11 US gallons, but owners of the car have reported fill ups from "empty" varying from 8 gallons to over 12 gallons.
Because of that, there is a very good chance that the onboard computer of the Prius was closer to the true fuel economy numbers than the 'fill up' numbers, and so the whole conclusion of the test is thrown in serious doubt.
And if we look at some of the obsessive fuel economy trackers out there, it seems more likely that the Prius got around 47 MPG US than 33 MPG US. For example, John1701a has a lifetime average (over 98k miles) of 47.9 MPG US with his second generation Prius hybrid, and he has used a gasoline/ethanol mix (probably E10) for most of that, which reduces MPG a bit.
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Toyota Prius vs Jeep Patriot: the great MPG test
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I'm getting over 50 MPG in my Prius. Only very short trips in cold weather give results in the 30 MPG.
This New Scientist article shows how badly the journalists are asking the wrong questions.
http://lookleap.com/environment.newscientist.com/a2/look
Obviously, since the real numbers are unknowable, they're closer to what we want to think they are, than what the other guy says.
You have to fill up at the same station at least 2 times to get a accurate reading of the last trip. I own a prius and at my regular station I fill up with 40L and at almost other stations I fill up with 42L. This is ofcource compenstated over 2 trips, one with bad milage and one with extreme good milage.
MPG is only part of the picture. The Prius also emits less CO and CO2, SOX, NOX, and particualates than the Jeep. This is especially important in low speed city traffic.
The Prius is meant for city driving, because if you actually look at the MPG at least in the US, the city mileage is higher than the Highway miles. As for the computer reading incorrectly, that is a problem, but it is something that has been a problem for years, ever since they have added that feature onto cars. I was a technician for seven years and I heard a lot of complaints about that.
To get the best mpg from a Prius you should leave the windows UP and the AC on automatic. As for the fuel bladder, I wonder if UK fuel pumps have the vapor return sleeves that are required in America. If you have a tight fit between the nozzle and the filler neck it might shut the fuel delivery off on one fillup but not the next. I'm assuming they made sure they started out with full tanks for both.
When it comes to getting the best mileage from a diesel, put it in neutral when stopped at traffic lights or when coasting. They use less fuel if they don't have to work against a slush box.
But the worst part of the test was they took them on a road trip, the Prius gets its best mileage IN TOWN AND HEAVY TRAFFIC which is how they are used in America. If you are living in Europe and you only use your car on the weekends for recreation while taking the subway during the week then a diesel will do just as well as a Prius.
I'm shocked that the journalists weren't aware of the Prius' special gas tank...
Obviously, the only way to conduct this test is to use an auxiliary visible gas tank with precise and clearly readable graduations, then use your own odometer that has been calibrated (or maybe a GPS would work). I think this is how Consumer Reports does it. Thus, you can tell exactly how much fuel was consumed and exactly what the distances were and formulate a reasonably accurate MPG. However, I would say the 160 miles just isn't enough distance to really determine much, and there are still a lot of uncontrolled confounds that I didn't see discussed in detail, like state of the cars (new, well broken in, recently tuned, tire pressure), and quality of fuels. But, as the author of this blog said its just a magazine article, and if we are blogging about it, then it was successful whether or not it was accurate.
fyi:
on our prius: if we drive cautiously (MPG wise), we can get consistent MPG at mid 50s. if we drive like a-holes, 90mph from LA to SF, we get mid 40s. the same result with a sleepy baby, parked with a/c on beside driving... yes, US gallons.
our pickup truck, it gets a consistent 13MPG
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My parents bought one of the first Priuses and had to track their mileage in order to qualify for the tax credit. So I know that the first Prius at least gets around 50mpg.
The more I think about it the more I suspect they forgot to top up the Prius before starting out (you can burn through a gallon without the fuel gage moving and if you only put in a couple of gallons sometimes the fuel gage won't reflect the addition). I've been driving a Prius for 4 years and I've generally obtained good agreement between the computer and the fuel pump method. If anything the computer has been pessimistic, when I figure the mileage myself I end up with slightly higher mpg (56 instead of 53, no big deal).
There should be cars out by now with substantially better mileage than both of these!
"There should be cars out by now with substantially better mileage than both of these!"
People buying Prius and other high mileage cars are sending the signal to automakers that these things sell, so make more of them.
Who cares. Just get a bicycle or use transit. No such thing as a green car.
If you really want to send a message to the automotive and oil companies, just stop buying their products. Most people in the world don't buy them. Join the crowd.
John Laumer is correct. Diesel has higher carbon emissions per gallon than gasoline, but the diesel engine is also more efficient (higher compression ratios and no throttling losses, though the throttling losses are less important in a hybrid which can run the gas engine more efficiently). This more than makes up for higher carbon content. My VW Jetta TDI routinely gets between the 40 and 45 mpg (biodiesel usually at 37 mpg, but until it all comes from algae, i swore that off for reasons other than cost). A regular Jetta gets in the mid-twenties. This means my diesel pollutes less (and has more torque!) than a "regular" Jetta. The best of both worlds is obviously a diesel electric hybrid.
John is not correct about the criteria air pollutants a diesel puts out. I am not sure about this car in particular, but the upcoming diesels emit much lower amounts of NOx and PM than earlier models. Not sure what a prius' CO emissions are, but a diesel runs at higher temperatures, so CO isn't usually a problem for diesels. The technology has completely changed since the '80s - computer chips, carbon filters, and a few other high tech gizmos (and new engine designs) make it a superior choice to gasoline engines. Now all we have to do is change our air emissions regulations, the way our refineries are tuned, and grow algal biodiesel! Of course, electric from renewables is the superior option, but this is a good stopgap measure.
Want a plug-in diesel electric hybrid, with solar panels on the top, anyone?
It's always funny when journalists try to measure something or even worse, when they have to do some unit conversions:)
Hey, at least this time they didn't look at the temperature gauge and wondered why the amount of fuel starts to increase when the engine warms up...
We could look a the positive side of this little study verses slamming it and saying how all mighty the Prius is. The plus side is that the Jeep got pretty decent MPT for being a midsize SUV and if someone is going to go the SUV route, this might not be such a bad option. Coming of course from the Green & Clean Mom who yes, drives an SUV!!
I'm glad you pointed this out though because their study was misleading and it is good to know.
Diesel fuel has a much higher energy value per gallon than does gasoline. Ethanol has much less energy value than gasoline.
You would expect a diesel engine to get rather good milage in a comparison with a gasoline/ethanol powered car. If I had a nuclear powered car and could run it for a year while only using a teaspoon of fuel, that would not necessarily mean that it was the more efficient vehicle.
Any comparison test should provide a calculation that converts the relative fuel values so that an accurate comparison can be made. I would recommend BTUs/mile. Otherwise it's really apples to oranges.
The weights of the jeep and Prius are not so far apart, either, which is another major factor in gas milage. Jeep is also a brick compared to the Prius, so extended highway milage at high speeds would suffer greatly.
It would also be useful to consider the lifecycle energy efficiency of the vehicles. The Prius has a lot more materials and manufacturing invested for its electric motor and battery pack. Its milage is perhaps 25% improved over what a car with a modest gasoline engine could provide. Does its improved milage ever really pay back that additional manufacturing energy investment?
The testers were not familiar with the Prius. They admitted not being able to engage drive initially, while waiting at traffic lights, where they officially began the test. I would be flusterred in this situation and in my haste to be ready for the green light would very likely forget to press the reset on the consumption screen. With unfamiliar drivers at the wheel and the mpg figure from a previous more competent journey I would expect the discrepancy which was reported.
The Jeep with the diesel engine is not available on the (USA version) jeep.com website. At least I can't find it. The test was done in the European diesel. Maybe we'll have the option to look at that one next year? They've been bragging about their diesels for a while now.
FYI: The Diesel jeeps in the US have the CDI label on the back of them. CDI = Common rail Deisel Injection.
They are readily available from all jeep dealers.
In addition, Mercedes/Chrysler are introducing a whole line of diesel engines into their fleet under the name of Blu-tech Diesel. The short of it is a 30% increase in fleet mileage. The Blue part of Blu-tech is a chemical reaction used to tremendously reduce hydrocarbon emissions.
Short and sweet= Prius. Auto writers are blind and ignorant when in comes to hybrids in general. Very rarely does one read an article that says much good about the Prius- probably because the writers have not driven one for more than a few minutes or miles and probably because they don't understand the BASIC concept of hybrid.
Eary to get 55mpg regularly(especially during times of peak battery efficiency) and with a little manipulation 60 mpg. There is a joy factor that is totally ignored reference value: watching people at the gast station look at my pump to see; if I were to sell it what I would get;sense of doing the "right thing" for society and even for those who are clueless about energy and one and on,.
First of all, why are we comparing an SUV with a sedan? It would've been more fair to compare the Patriot with a Ford Escape. My only guess is that that article was attempting to get folks to get used to diesel fueled vehicles. Does anyone agree?
Our 4 yo Prius will get well over 50mpgs consistently on the highway, depending on who is driving it. My not so green hubbie took my Prius for his long commutes, and now brags EVERY time he walks in the door that he has improved it yet again! He gets over 55 mpg every tankful now.
It gets 44mpgs by ANYONE, even aggressive drivers, like my son. My daughter, who drives conservatively, but isn't motivated to try to get the best out of the car, she just drives, whatever! She gets 53.
In winter, on short trips on back roads, we usually get 40, but on the highways in winter we get 48 easily.
My next car will have to be a Prius (minivan is a 1994 - hopefully it will last a few more years with low milege driving).
But where are the other choices???? I thought my 2004 Prius would be an interim car, until something even better came along. Geez!
That's not an SUV. It's just a square car with a Jeep emblem. It's the only Jeep that ISN'T "trail rated." There's no sport or utility in it, only brandng. It's an inefficient grocery getter, but when you put the label SUV on it, it becomes best in class.
P.S. How much gas did they waste with this test?
I think they should have begun the comparison at the gas station after topping off the tanks but even so I bet they were shifting the Prius into 'neutral' while coasting or stopped at traffic lights. That trick increases the mpg of my 2002 Ford Focus (gas) by 10% because the engine isn't working against the torque converter and brakes at stop lights and kinetic energy isn't being used to compress air when coasting (compression braking).
IF YOU TRY THIS TRICK with a Prius you completely disable regenerative braking (charging batteries while coasting and braking) and prevent the engine from charging the battery at stop lights (put your foot on the brake, the engine will run to warm up the catalytic converter but will charge the battery at the same time)
Don't try to be more clever than Toyota's engineers!!!
I concur that the prius should have gotten about 47mpg. I've had mine for nearly 40k miles, and receive consistently 47-48mpg in the summer, and 45mpg in the winter. Seems like another test is in order.
Since diesel is (20%?) more expensive than gasoline, since it carries more btus per gallon, for equivalent mileage the Prius could have consumed 20% MORE gallonage and still have been equally efficient.
I have had my prius for almost 1 year. I have ALWAYS gotten at the very least 48 MPG... I dirve up and down the east coast sharing my time between RI in the winter and MD in the fall, out of all the times i have had to fill up only ONCE was it less than 50 mpg, usually is 52.2. Best investment EVER.
The Prius is particularly disadvantaged in this kind of test because there are so many variables which can affect the measurements. The Toyota spokesperson correctly mentioned air pockets which can easily develop if the tank is filled too quickly. Also you must not fill when the power is on and "ready" is showing. This can lead to some big anomalies as the pump cutoff operates far too early in this situation. Then if your next fill is with the power off you think you have used much more fuel than you actually have. This will not confuse the computer however!
I started out wondering why they choose the Jeep Patriot Diesel as the vehicle to use for comparison... I mean, there are dozens of others they could have chosen from - so I looked more into the Jeep Patriot. After finding out that the diesel isn't even available in the US right now made me even more curious. That's when I found out that it has received a couple green awards over in the UK and a couple (John and Helen Taylor) took one through 6 countries on a single tank of diesel (nearly 700 miles on one tank - averaging out to over 67 MPGs US from the stock vehicle). The drive was verified by an independent judging official. I'm not sold on it but now understand why it was chosen to go head to head. It may not be there, yet. but they are heading down a promising course it seems.