Since I have always maintained a fuel mileage log as long as I can remember on all my cars this comes as a surprise to me. So far, I have only fueled the "TessX" 3 times and have noticed each time the mileage indicated by the trip computer is about 2-4 mpg higher than what I calculate. At first I thought it was an anomaly, but after 3 times I have to wonder?

Since this hasn't been posted before, I can ASSume that no one else has challenged the accuracy of the trip computer and has taken it at face value as being correct?

By my calculations at fillup today I was getting 21.6mpg, the trip computer indicates 23.6mpg?

Can anyone else with a Navi verify this?

 

I've discovered the same thing. At first, I thought it was just a difference in how much gas was put in the tank (topping off). But after several tanks the trip computer is consistently high.

 

i don't think its very accurate. the range seems to change pretty often... ie, i started the car and the range said 280, and after i got to my destination 15 miles later, the range still said 280.

also, after the first 100 miles, i'll have averaged ~24 mpg. and the estimated range will be ~400 miles. but even if my average goes up to ~25-25.5 mpg, i can't get to 400 miles. usually have to fill up at ~360 miles.

 

The mpgs computed by the trip computer average about 1 mpg higher than what I calculate myself.

The "Range" number seems relatively useless.

 

That's just a "feel good" number for the lead-footed you.

 

This is precisely my point, is the system this inaccurate or is it possible it computes data differently than we do.

If I record miles traveled and divide by gallons consumed at fillup, I expect to calculate miles per gallon. To my way of thinking, this is an average since the last fillup?

When the trip comp indicates average miles per gallon, could it be using different data to calculate this than we are, if so is it more accurate?

 

This probably explains why some people are getting very high mileage figures. Figures that are too high to be true.

 

Dunno -- I've found mine to be accurate within about 1 mpg.

About the "range": I think it's useful, if you understand how it works. A couple of things:

(1) Just like Honda's/Acura's fuel gauges, it's very "conservative." As we've said before, it's not really "miles to empty" but "miles until you'll have only about 3 gallons left." I do find that at least somewhat useful, although I'd prefer "about 1 gallon left."

(2) The "range" keeps recalculating itself according to what kind of MPG you're getting lately -- not from second to second, but apparently it does use some kind of "moving average" (Wall Street phrase).

Actually I'd be interested to know what kind of "moving average" gets used. Anybody know? (I imagine it would be something like, "Average MPH during your last [fill in some amount of time or number of miles].")

 

Let me say first that I have no idea how this is calculated....

But if I had to do it, I'd use the instantaneous MPG data together with your total miles traveled during the sample time (recoreded by your digital odometer) to get an "instantaneous gallons used" number. The data points can be integrated (summed) over time to get a total number of gallons used so far. This can be compared to miles travelled to get the "moving average" MPG you spoke about. Then you can speculate about range based on this "total MPG" and the availible fuel in the tank. Make sense?

 

The problem with that is you'd get ridiculous figures for a while after each time that the "digital odometer" gets reset.
BTW I can't tell if you're referrring to the one on the dash -- i.e. the "usual" one -- or the one on the trip computer. They're completely independent. I imagine probably the usual one.

 

By "sample time" I meant the amount of time between recalculations of MPG, not time between fill-ups. So it doesn't matter which odo you use or whether the trip meter(s) was/were reset. The distance recorded between those two points should be the same on all three things. Sorry it was unclear.

 

And actually, doing it this way would account for the "fuel tank is bigger than advertised" thing. If the navi is making calculations based on a given size fuel tank and it's actually bigger (as people have shown), then range calculated by navi should go to zero long before you run out of gas. Right?

 

That thing about not knowing which odometer you meant was just a side issue.
Main thing was that there would be times when the figure would be ridiculous.

And, still a problem the way you re-define it, actually more so, isn't it?
Because, MPG gets recalculated CONTINUOUSLY (and besides, BTW, it starts all over again every time you reset the odometer on the Trip Computer, not just with each fill-up).

Maybe not too many people knew those things, in which case they qualify as Easter Eggs (or maybe lumps of coal).

 

Nothing digital is TRULY continuous. It might be calculated a million times per second, but that's still not continuous. You can do the process I proposed a million times a second, too.

Now THAT, I didn't know. I guess I just don't know enough about how the navi does its thing to answer this for real. I'll just give it up.

Edit: Does the navi have it's own separate owners' manual? or would this be a service manual question?

 

Yeah, my bad -- It's not continuous, just every millionth of a second. Good point.

No, Clutch -- we need you!!

Yes. Pretty big one.

 

Ah. So it just tells you how to do stuff and now how stuff works. That won't help.

Man, with all the "easter eggs" in the Navi, I'm kinda wishing that I'd gotten one. I'd probably never use the map, but things like adjusting the odometer for different tire sizes is very cool.