We're going to be saying good bye to our long term 2007 Saturn Aura XR test car soon so I was given the keys to arrange it's sale. When I climbed in I checked the fuel economy on the onboard computer and it read 16.6 mpg from a recent variety of drivers. I zeroed out the meter for my 31-mile commute home which has a lot of stop and go traffic. When I got home it was reading 22 mpg. It's lifetime average is 19.9 mpg.
The next morning I zeroed it out again for my morning commute. I set the cruise control and kept pace with traffic (no hypermiling here). A block from the office I took this picture reading 30.2 mpg.
So, if I owned this car, for this commute, I could make it to my office on about one gallon of gas at a current cost of $3.50 one way.
It's interesting how many cars are capable of a huge range of different fuel economy levels depending on the conditions (city vs. highway) and driving styles (calm vs. aggressive). You can't do a lot about the traffic (except leave earlier or change your route) but you can change your driving style.
By the way, the Edmunds.com Used Car Appraiser puts the current value of the Aura at $17,923 for a private party and $15,938 as a trade-in. A year and a half ago we paid $26,794 for it.
Philip Reed, Senior Consumer Advice Editor @ 21,504 miles
carmizvi says:
10:21 AM, 10/ 6/08
I'm going to miss the Aura. What else is there in the fleet that merits a good old-fashioned bash fest?
Oh yeah, the Flex.
(Kidding! Curiously, I like 'em both for different reasons. A fridge...c'mon, folks!)
joefrompa says:
10:32 AM, 10/ 6/08
Philip - The real question is: how accurate is the gauge vs. reality?
No offense meant - My 08 Legacy GT reads about 2-3 mpg high. My wife is getting ~27mpg on her steady 32 mile commute (which is mostly back roads and accelerating to 50 before coming back down). But in reality, she's getting about 24mpg (still great for the car).
Joe
jahfakin says:
11:06 AM, 10/ 6/08
my one way commute to work is 45-50 miles (depending on the route). But because of people's bad driving habits (i.e. drivers with no lane discipline), I cannot use cruise control on 1/2 of my commute. I just wanna drive at 75mph (65mph speed limit) with cruise control on, but for some that's too slow, and others it's too fast.
joefrompa,
I always trust the computer when it comes to MPG. I think the data is computed by how much fuel is pumped through the injectors. If I recall correctly, this is how MythBusters measure the mileage in their "Great Gas Conspiracy" episode.
If you use the gas pump method....then the data is more like to be inaccurate. On hot days, you are actually getting less fuel than what the pumps says, and on cold days, you can be getting slightly more fuel....assuming the gas pump is calibrated correctly. I believe most gas pumps are calibrated to 60 degrees Fahrenheit. (but this can differ depending on region/state).
If the car is equipped with a bladder gas tank, like the Prius....then there is now real way to calculate the actual mileage...you must use the on board computer. Since the "net" capacity of a a bladder gas tank will vary depending on the temperature.
jahfakin says:
11:16 AM, 10/ 6/08
Correction (no edit feature):
I noted the wrong Myth Busters episode....the correct one is "Drafting a big rig saves fuel", which was confirmed.
http://kwc.org/mythbusters/2007/06/episode_80_big_rig_myths.html
"....Andrew Smith, test engineer, who helped them hook up a computer to the fuel injection system to accurately measure the fuel consumption."
dougtheeng says:
11:41 AM, 10/ 6/08
That depreciation isn't too bad, and the car may be a decent used pick up for someone.
Those gauges are hideous though.
ahightower says:
11:57 AM, 10/ 6/08
Even if it's off by 1-2 mpg (as in my GMC), that's not bad for a decent sized car with a fairly powerful V6.
allenychung says:
12:08 PM, 10/ 6/08
We had one of these gauge vs reality discussions a while back, I'm in the camp of not trusting the gauge, while others were saying they trusted the gauge more because they couldn't trust if they can fill up their tanks to full everytime.
Been resetting the gauge on my Mazda 3 the past three fill ups, and it's fluctuated between 2 to 3 MPG lower than my own calculations, been going to the same gas station and using the same pump, and I trust in my fill up skills.
joefrompa says:
12:18 PM, 10/ 6/08
I'm calculating 34% depreciation with a private party sale over less than 2 years. I don't think that's acceptable, but I just bought a car with about the same depreciation :)
I did not mean to impugn the gas mileage if I did...I find it completely reasonable that this car would get 30mpg. But I do impugn on-board fuel economy estimators.
Jahfakin - Supposedly, a ScanGauge or similar OBDII fuel economy estimator can be spot on because it measures actual fuel used by mileage driven. I have no idea why so many cars trip meters are not as accurate. But most are not accurate.
You raise valid points about testing fuel economy via the "top off and divide" method. For me, I don't top off (I stop at the click) and I tend to fuel up at near identical temperatures week to week (I'm either filling up at 7am or 7pm, usually within about 10 degrees fahrenheit). From what I understand, the variability is not that great. Maybe a tenth of a gallon?
Regarding the Prius - Same thing. You are using gas used vs. mileage driven. If the prius is filled up at a near-identical temperature, then how much variation in filling a capacity is there?
Joe
bepperb says:
01:55 PM, 10/ 6/08
Sure, for one tank I can see how you might be off.
But over a series of tanks, you'll never get more accuracy than the "how much gas did I put in" divided by "how many miles have I driven" and to say otherwise is ridiculous. If I've driven 20,000 miles since I bought my car, and I've used xxx gallons of gas, no computer is going to be more accurate than that. And I assume Edmunds keeps this tight of numbers...
The ScanGauge has to be setup to a particular vehicle, then fine tuned. They are close, but most people are one or two tenths off. I assume most car comptuers are that far off as well.
brn says:
01:59 PM, 10/ 6/08
I'm with bepperb. I get my gas at the same place (not the same pump) every time. Sometimes it's a little higher than expected, sometimes a little lower. However, the average over multiple fills is pretty darned reliable.
The only potential for significant error is if the speedo is incorrect. That would also be a problem with the onboard computer or a scangauge.
joefrompa says:
02:18 PM, 10/ 6/08
Yeah, I plan on oversizing my tires in my Legacy GT (225/45/17 instead of 215/45/17) which will make me read about 4% low on the speedometer. Outside of that, it's a pretty safe bet :)
Joe
jahfakin says:
03:40 PM, 10/ 6/08
joefrompa,
I really don't know how much variation in filling capacity there is on the Toyota Prius. I don't own one. But since I'm interested in getting a Hybrid, I'll be looking into this.
It turns out that the Nissan GTR uses a similar bladder tank...they call it "a saddle-bag design" (see link below).
http://blogs.edmunds.com/roadtests/2008/09/2009-nissan-gt-r-fixed-againagain.html#more
Also, you can confirm how much your speedo/odometer is off by using a GPS. it should read the true speed and distance.
bimmerjay says:
05:08 PM, 10/ 6/08
"Those gauges are hideous though."
Haha, yes... yes they are. So is the corrugated cardboard-looking IP face.
the_big_al says:
06:04 PM, 10/ 6/08
I have never had a gauge meter in any of my cars and so the only method I have ever used was the fill-up method. Everytime I have done (I check my mileage almost every time in my van), I get pretty close to accurate results. My van sees about the same type of driving every day as does my truck and so I usually average about the same MPG. Sometimes a little more or less, but usually not by more than 1 GPM.
It also helps that I always try and use the same station to fill up and the same pump at that station as well. If I am lucky, the same attendant also fills the tank as well (in OR you can't pump your own gas grrrr).
opfreakx says:
06:36 PM, 10/ 6/08
most car mpg gauges, dont read off injectors. alot work off the mass flow sensor, which is not as accurate
brn says:
05:41 AM, 10/ 7/08
"Also, you can confirm how much your speedo/odometer is off by using a GPS. it should read the true speed and distance."
Better yet, use the mile markers on the side of the road. Old tech is great.
1487 says:
07:32 AM, 10/ 7/08
I have found the trip computer to be pretty accurate. The few times I calculated mileage myself it was very close.
What we need to know is how this depreciation compares to import cars in the fleet. We keep hearing about the superior resale value of the imports so I want to know how the numbers stack up. What were the residuals on the Camry and Altima?
misterfusion says:
08:49 AM, 10/ 7/08
So now the gauges are hideous? One of Edmunds' first posts on this car was entitled "Cool Gauges". I can see how the style of the corrugated strakes behind the cluster might turn some people off, but I think the actual gauges themselves are quite attractive. And I usully don't like pod-style gauges!
Even if you think it's ugly, come on -- at least they're not Ford gauges.
bimmerjay says:
09:30 AM, 10/ 7/08
"Even if you think it's ugly, come on -- at least they're not Ford gauges."
I'll give you that. :-)
brn says:
10:22 AM, 10/ 7/08
misterfusion, it depends on who was driving it and what their mood was. That's the problem. It's all very subjective.
joefrompa says:
11:42 AM, 10/ 7/08
1487 - Good point, the Camry and Altima would be great comparators. Along with their resale, post the months they were bought and sold in.... (buying a 2007 model in July 2007 typically means it's resale is lower than if it was bought in September 2006 as a 2007 model and sold one year later).
Joe
misterfusion says:
12:19 PM, 10/ 7/08
brn: I agree with you in principle. But it reminds me of a quote by Mark Twain, who said, "Styling is subjective, but the Accord is ugly."
Of course, I could be misquoting that...
bimmerjay says:
12:33 PM, 10/ 7/08
"That's the problem. It's all very subjective."
It's not a problem, it's reality. Every editor is entitled to their own opinion, and since this is a BLOG, we read it to see them raw, individual and unfiltered.
If you don't like that you should stop reading now and stick to the LT intro and wrap-up articles, since those generally lack individual opinions and capture the overall impressions.
brn says:
05:23 AM, 10/ 8/08
bimmerjay, the problem is that it gets stated (and accepted) as fact. Otherwise, you're correct.
dougtheeng says:
05:46 AM, 10/ 8/08
"bimmerjay, the problem is that it gets stated (and accepted) as fact. Otherwise, you're correct."
Anyone who considers an opinion regarding styling as "fact" needs a knock on the head. There have been so many instances on these comments where people state in their arguments that a vehicle is better looking, or best looking in class, etc. It makes me laugh. We all have opinions, and its not surprising they don't always jive. Thats what keeps things interesting.
1487 says:
05:59 AM, 10/ 8/08
the gauges in this car look better than the cheap looking units in the Accord. And the entire cluster is backlit like Honda used to do on the Accord. I find it interesting that BMW fans would be criticizing the gauges on any other brand of car. BMWs have some of the dullest gauges on the market and they are totally unbefitting of an expensive car.