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Old 09-04-2012, 01:30 PM
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Exclamation EVIC MPG estimate - How accurate is it?

I have a 2012 Laredo V6 4x4, Laredo E, OR1, Security and Convenience
Jeep says Est 16 City est 22 highway

I did a 1 tank study to see the accuracy of the EVIC's estimated MPG usage.

Aug. 27 at 5:31 AM I filled up with 21.984 gallons (brought it to full) Odometer reading was at 14,095 miles. Reset the evic MPG display.

Drove normally for 1 week.

This morning when I pulled up to fill up the next tank of gas. I noticed that when I pulled in my MPG estimate was at 22.3 MPG
I put in 21.162 gallons of fuel. Mileage was at 14,538.

If I do the manual calculation 14,538-14,095 = miles driven on this tank = 443 miles.

443 miles/21.162 gallons = 20.933 MPG

So MPG estimate is off 22.3 - 20.933 = 1.367 MPG or a little more than 6%

Has anyone else tried doing a comparison?

I will continue to do this over a more extended period of time and post results to this thread. Feel free to add your data.
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Old 09-04-2012, 02:19 PM
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Re: EVIC MPG estimate - How accurate is it?

Here's the problem, and I think a lot of people ignore this when claiming the EVIC is inaccurate.

You're counting on the pump shutting off at the exact same fuel level in the tank every time. That's just not going to happen. Even if you go to the same pump at the same gas station I bet it varies by more than several %. Now if you go to a different pump, or even worse, a different gas station then the fuel level in the tank when the pump shuts off will be off by even more.

I suspect the fuel level could easily vary by 1/2 gallon or more from fill up to fill up. I've often had the pump shut off when it was several gallons short of being full and didn't realize it until I was driving and noticed the gauge was showing 1/8th less than full.
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Old 09-04-2012, 02:27 PM
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Re: EVIC MPG estimate - How accurate is it?

The other thing to keep in mind is that the EVIC display only considers the last 100-200 miles or so, not since reset and not over an entire tank. Thats a bit different than other vehicles I've owned. If you drive consistently (say highway) throughout the tank, the EVIC and your manual calculation will be closer. That being said, most here think the EVIC is a tad optimistic.
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Old 09-04-2012, 02:35 PM
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Re: EVIC MPG estimate - How accurate is it?

Quote:
Originally Posted by ColdCase View Post
The other thing to keep in mind is that the EVIC display only considers the last 100-200 miles or so, not since reset and not over an entire tank. Thats a bit different than other vehicles I've owned. If you drive consistently (say highway) throughout the tank, the EVIC and your manual calculation will be closer. That being said, most here think the EVIC is a tad optimistic.
Huh? The EVIC calculates your mileage average from the last time you reset it. Why do you believe it's a 100-200 mile rolling average?
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Old 09-04-2012, 04:05 PM
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Re: EVIC MPG estimate - How accurate is it?

I have to agree with Doc d.

It is DTE that uses a weighted average.

Distance To Empty (DTE)

Shows the estimated distance that can be traveled with
the fuel remaining in the tank. This estimated distance is
determined by a weighted average of the instantaneous
and average fuel economy, according to the current fuel
tank level.
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Old 09-04-2012, 06:12 PM
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Re: EVIC MPG estimate - How accurate is it?

This has been covered a bunch and the EVIC is usually 1 to 3 mpg's off. This is common on most vehicles with mpg averages. My motorcycle is usually 2 mpgs off as well and I fill it up to the same spot everytime.
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Old 09-04-2012, 06:26 PM
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Re: EVIC MPG estimate - How accurate is it?

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Originally Posted by tnjeep View Post
This has been covered a bunch and the EVIC is usually 1 to 3 mpg's off. This is common on most vehicles with mpg averages. My motorcycle is usually 2 mpgs off as well and I fill it up to the same spot everytime.
I don't know how you could possibly know the EVIC is inaccurate with no good way to verify you are filling the tank to the same level every time.

I'm not saying it's not inaccurate. I'm saying that no one I've seen has proven it to be inaccurate because they are using an extremely inaccurate method of determing how much fuel they burned between fill-ups.

For all we know the EVIC is underestimating the mileage.
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Old 09-04-2012, 06:58 PM
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Re: EVIC MPG estimate - How accurate is it?

Mine thinks I average about 24.9. See the chart for my LTD mileage calculations. Yes, I know that I may not get the exact same fill every time, but this will average out over time. The computer is a bit optimistic.

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Old 09-04-2012, 07:12 PM
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Re: EVIC MPG estimate - How accurate is it?

Quote:
Originally Posted by Doc_d View Post
You're counting on the pump shutting off at the exact same fuel level in the tank every time. That's just not going to happen. Even if you go to the same pump at the same gas station I bet it varies by more than several %. Now if you go to a different pump, or even worse, a different gas station then the fuel level in the tank when the pump shuts off will be off by even more.

I suspect the fuel level could easily vary by 1/2 gallon or more from fill up to fill up. I've often had the pump shut off when it was several gallons short of being full and didn't realize it until I was driving and noticed the gauge was showing 1/8th less than full.
That averages out if you log the mileage every fill up (or use an app). I do and it has only 1 time been where I got 1-2 mpg higher than the EVIC (thus I had a partial fill that fill up and would expect to be low mpg the next fill up). EVIC is always 1-2 mpg higher than hand calculation. So over almost 2 years it only happened once that the EVIC was lower, they software is programmed to error on the optimistic side.

I have even tried this over about a 1 year period of not resetting the mpg thinking that it was being effected by the multiple resets (my BMW average was much better if you didn't reset, but worse for that tank). Over a 1 year period they 1 year average was about a perfect match. EVIC 1-2 mpg high.
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Old 09-05-2012, 05:56 AM
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Re: EVIC MPG estimate - How accurate is it?

Doc, I take the same 350 mile round trip twice a week that is 90% interstate. I use a few different stations near my home and always fill up right before I get back home. The Jeep almost always takes 15.25 gallons to fill it back up (23mpgs). I know both methods (hand calcl and computer) are not perfect but for the evic to be right the gas station would have to short me over a gallon of fuel everytime to get the 25 mpgs that the EVIC is saying (350 miles/14gallons = 25mpg)
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Old 09-05-2012, 06:49 AM
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Re: EVIC MPG estimate - How accurate is it?

Mine is spot on. Never more than a couple tenths off what I calculate.
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Old 09-05-2012, 07:58 AM
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Re: EVIC MPG estimate - How accurate is it?

Yeah the topic was discussed a lot near two years ago, and thats just how it works. The Jeep displays long term mpg differently than other vehicles. It drops aged data regardless.

The computer that calculates and displays mpg knows exactly how much fuel it asked the fuel injectors to squirt and just how much distance the distance sensors tell it the vehicle has travelled. There are no sensors for exactly how much fuel is being used as a double check. The computer has no idea if one or more of the injectors are squirting a few more drops than requested, or if the tires are worn, or the speed sensor is a little off today, or fuel is evaporating (or leaking), or if its volume is expanding/contracting due to temperature, or if your neighbor is syphoning off some fuel.. you are not going to get the same readings or calculations as the manual method. What you are seeing in this thread is vehicle to vehicle variations in tolerances. Typically the EVIC will be a little optimistic, I don't know of a vehicle thats is not a bit optimistic. It is intended as a tool that pushes you drive the vehicle with optimum fuel efficiency. Look how often mpg is discussed here

So to answer the question of just how the EVIC mpg compares to manual methods of determining mpg, it varies from vehicle to vehicle. Some see spot on, some see 2 mpg difference, the EVIC being optimistic. Tracking mpg is good, however, as an advanced indicator of issues. A sudden drop or rise in mpg should be investigated.
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