Does anyone else's car computer lie about MPG?

"Chairman Kaga" (mike-mckinnon) 03/26/2014 at 10:10 • Filed to: None

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My 2008 CRV consistently tells me I'm getting 1.5-2 MPG better than actual calculations done in Gas Cubby report. I polled the CRV boards (and my God is that the saddest place on the Interwebs or what... shudder) but so few people consistently track their fuel economy or do it correctly I didn't get a good sense.

Why/how would it do that? I use consistent methodology for tracking mine. Same station and even pump as often as possible, my weekly routes are usually more or less the same, my driving habits are regular. I dunno.

FYI - car computer tells me 22.8 MPG, Gas Cubby says 20.7.

StoneCold > Chairman Kaga 03/26/2014 at 10:15

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To paraphrase a bmw e39/38 forum comment:
"At least the odometer is more trustworthy than that lying pirate hooker of an MPG calculator."

Party-vi > Chairman Kaga 03/26/2014 at 10:15

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The computer in my 330Ci is a tad optimistic about my MPG.

RazoE > Chairman Kaga 03/26/2014 at 10:16

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The IS300 mileage gauge is useless. It shoots up to 80 mpg anytime you're off the gas and coasting, but it won't return anything better than 16 mpg.

Patrick Nichols > Chairman Kaga 03/26/2014 at 10:16

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I wish my last car was lying but it was sadly telling the truth... (2000 Volvo S80 2.9L averaging less than 15 mpg)

Yowen - not necessarily not spaghetti and meatballs > Chairman Kaga 03/26/2014 at 10:17

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I reset my MPG counter every tank and it is almost always within .5mpg of my hand calculated average. I drive a 2010 Taurus SHO. Can't wait for it to warm up, my mpg's have just been plummeting, haha.

If you are curious:
https://www.fuelly.com/driver/yowen/t…

Jeff-God-of-Biscuits > Chairman Kaga 03/26/2014 at 10:17

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I wonder if it only calculates while the car is in motion? Do you spend a lot of time at idle, parking lots, that sort of thing?

MR2_FTW - Group J's resident Stig > Chairman Kaga 03/26/2014 at 10:18

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Fuelly would be a good place to look for real-world fuel economy statistics

http://www.fuelly.com/car/honda/cr-v…

ttyymmnn > RazoE 03/26/2014 at 10:19

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Interesting cluster. Looks like a wristwatch.

Slave2anMG > Chairman Kaga 03/26/2014 at 10:20

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All five of the VWs I've had with a gas mileage computer was about 1.5-2 mph optimistic...these were all company cars so I did a lot of miles in them.

StoneCold > RazoE 03/26/2014 at 10:21

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I loved doing that in my 02 Grand Cherokee. Get up to 65 mph or so, then coast down a hill and watch the instantaneous digital counter hit 100 :D

davesaddiction @ opposite-lock.com > Chairman Kaga 03/26/2014 at 10:22

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Pretty sure they all are. There may be a way to alter the correction the computer uses (there is a way in my car, but I haven't taken the time). At least your actual is ~20, not ~15, like my '08. I'd wager I get more smiles per mile, though...

Hermann > RazoE 03/26/2014 at 10:22

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These indicators measure instant consumption. And rely on what's currently happening. So, as you said, it's useless. Of course when you're on the throttle it'll indicate 2mpg and when you're lifting (you pussy) it'll shoot to 80, but it's useless for a real gauge of what's your actual consumption. I don't understand what they actually mean by putting it there.

On the other hand, I consider it a very addictive game.

RazoE > Hermann 03/26/2014 at 10:27

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It also shoots up while I engine brake. Love that exhaust burble!

davedave1111 > Chairman Kaga 03/26/2014 at 10:28

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Fuel leak? :)

jariten1781 > Chairman Kaga 03/26/2014 at 10:38

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On the FiST it's dead-nuts accurate. GTI not so much, but close. Altima Hybrid I rented read high by 4 mpg consistently over 3 tanks. It's a crap shoot.

The WB > Chairman Kaga 03/26/2014 at 10:43

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Most of these gauges are just a vacuum/load gauge. The actual numbers are not calibrated.

I track every tank by filled volume vs. mileage. Thats less accurate, though easier than mass/mileage because I don't want to weigh out my fuel every time, but it's eons better than a computer estimation. I don't even know why those gauges exist, I have never looked at them or treated them as truth.

Hermann > RazoE 03/26/2014 at 10:43

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Yeah. ECUs "sense" that the engine is revving, but is not "applying power" to do so when engine braking, then it kind of cuts the fuel injection and you basically drive while not using fuel. Pretty awesome.

I remember the first time I saw an onboard computer on my dad's friend Chevy Omega when I was a kid. We went downhill and it went straight to 99.9km/l, I said "whoa, that's an economical car!". They all laughed. I only later found out that Omegas had the ancient 4.1 Liter straight six engine adapted to ECU, so... not economical.

Party-vi > RazoE 03/26/2014 at 10:46

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Less of an MPG gauge and more of a manifold vacuum gauge.

Also, dat chronograph cluster. *drool*

Agrajag > Chairman Kaga 03/26/2014 at 10:48

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I've only tested it over single trips, but it was pretty accurate, only being off by tenth each time.

2009 GTI

efme > RazoE 03/26/2014 at 11:07

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its likely accurate. I can't tell if you know that you get like 3mpg when you accelerate ;)

efme > Chairman Kaga 03/26/2014 at 11:08

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One variable is pumps aren't always accurate. I recall reading that they can be up to 10% inaccurate and still be approved for use

quarterlifecrisis > Chairman Kaga 03/26/2014 at 11:10

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My C6's display is consistently off, my actual calculations (every tank is always a full fill up and tracked in excel, and I try to park on level surfaces and only fill until the auto shut off on the pump kicks on to eliminate inconsistensies there as well) show me returning usually 1-3 mpg better than what's displayed.

Yowen - not necessarily not spaghetti and meatballs > jariten1781 03/26/2014 at 11:24

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Interesting, my Ford is very accurate as well...

Chairman Kaga > quarterlifecrisis 03/26/2014 at 12:56

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I'd rather have your problem.

Chairman Kaga > Jeff-God-of-Biscuits 03/26/2014 at 13:06

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Nope to both questions. I spend a lot of time moving veeeeeeery slowly, thanks to Austin Traffic. It's always calculating though.

Chairman Kaga > MR2_FTW - Group J's resident Stig 03/26/2014 at 13:07

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And I'm right int he majority range, too. This thing gets horribly disappointing fuel economy. My wife's '14 Highlander, which has a 277 hp V6 and weight almost twice as much gets the same numbers, more or less.

StoneCold > StoneCold 03/26/2014 at 13:21

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Found it:

http://forums.bimmerforums.com/forum/showthre…

Boxer_4 > Hermann 03/26/2014 at 23:30

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Our Outback has a similar setup. From what I gather, the purpose of this style gauge is to make you more aware of your driving behavior in relation to fuel economy, and to help you improve both. Basically, it's there to get you to accelerate more gently, drive more gently, etc. The gauge is there to help you keep your instantaneous mpg up, which translates to a higher average mpg. I have used that gauge in this way, and it does work for improving fuel economy. However, the Outback's 3.6L flat-6 makes improving mpg hard to stick with ;)

JoelA237 > Chairman Kaga 03/27/2014 at 05:01

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My 2010 forester always read low. It would say 28 avg and I would be pulling in around 30-31 (90% highway)

Hermann > Boxer_4 03/27/2014 at 07:02

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This setup is more interesting. It's not a number, it's a + and a -. And it makes much more sense.