EVIC AverageMPG.... how the heck is this calculated!?

[colsar]

I reset my average MPG on the EVIC, drove to Florida and Back (about 1500 miles). My average was just about 24 mpg.

I am on my second tank of gas since getting home, so that is probably about 400 miles. I am down to 18MPG. Before the trip I was getting 16-17 average with my normal driving routes and patterns.

How the heck could it have dropped so fast! If I normally get 16, I would figure that after 1500 miles of driving around home my average mpg should still be about 20mpg (average of 24 and 16). How can I be down to 18 after just 400 miles when I have 1500 miles in the calculation at 24mpg!!!

I must be getting about 2mpg if that's correct!!! It seems like it is giving me a more current average mpg. Does it only calculate it based on the last fill up? last 500 miles? last 1000 miles? I assumed it would be from when you reset, but it doesn't look like it!

[moparknighthawk]

I am not sure. Try calculating the mileage yourself using the tripometer. (you should have two). Fill up then, miles/gallons used at next fillup. Compare that the the EVIC. Mine has been averaging between 18 and 23 MPG overall in the last 14 months and 14,000 miles. Recently my average has been 21 to 23.

[colsar]

I have my receipts, I should pull the ones starting on the day of the trip. I know the miles for the trip and could come real close to estimating the miles driven since returning home.

[bigkevin20]

I think it only works for the last few minutes. That damn thing so temperamental she never can make up her mine. Sounds like my chic. lol... Well as soon as I get off the high way it drops dramatically. I can reset while Im going 70 on the highway and stay above 22 mpg take the nxt exit go around the block and stop at 711 and I'm down to 14-17. Or if Im on the highway and I floor it a quick 80 to 100 burst and down she goes takes a while to come back. I guess thats what you would expect though, big engine high output.

[KWhale]

Colsar - A lot of people make the same assumption that you did. The MPG display on the EVIC is not an average fuel consumption since you last hit reset. The computer is just calculating how much fuel you have burned in the last minute or so, takes how far you've driven during that time, and calculates the MPG for that time frame. While it's probably pretty accurate at what it does, it has nothing to do with the long term MPG you are getting.

Jotting down the miles traveled and gallons used is the only accurate way to figure out your mileage. It's actually even better if you can do the MPG calculation on 2 or 3 tanks of gas, rather than just 1. One reason is when you fill up, you don't always fill it to the exact same level as the previous tank. If you average over a few tanks, this error is mostly averaged out. Another reason is that gas is volatile and the temperature outside when you fill up actually makes a small difference on the actual volume of fuel you are getting. A gallon is not always a gallon lol.

[bigkevin20]

So I was rite.

[colsar]

Larry,

Thanks for clearing that up. My wife's Pacifica seems to keep long term MPG and this one wasn't making any sense!

[moparknighthawk]

On my EVIC, it never varies that much at all between city and highway driving. Maybe mine is a little more accurate, or I just have a light foot.

[Super T]

On my EVIC, it never varies that much at all between city and highway driving. Maybe mine is a little more accurate, or I just have a light foot.

You have a light foot. I went a few thousand miles on my RT w/ no resets and it'd still swing 3 mpg when I took roadtrips.

[PaCharger]

just checked map

Remember, if you were going to Florida you were going downhill and coming back uphill.

[MikeEast]

On a somewhat related note, when I'm in the gas-mileage screen and do a reset, 'reset all' shows up - what exactly does 'all' imply?

What's interesting is that if I go to the gas mileage screen and start the car, reset it (goes to 0) and slowly drive off, it goes to '9.5' mpg and will only show 9.5 until it warms up (some). I haven't correlated any exact temperature, but I'm only seeing 9.5 all the way out of my subdivision.

I've noticed that the gas mileage readout is approximately realtime for 30-45 seconds or so, which I don't care for - I'd like to see it be a constant realtime one like Chevy uses. At least the 2003 MonteCarlo SS does anyway.

Mike

[KWhale]

MikeE - that reset to 0 and then getting 9.5 mpg readout is not a temperature thing. The computer just doesn't have enough data to give you an accurate readout, since you just reset it, and just started the car. It takes a minute or two to read tank level, distance traveled, etc before it can give you an accurate reading of your current mpg.
It's the same when you restart your car without resetting it to 0. The number you see displayed is just the same number you had when you shut the car off last time. In a minute or so, it will have enough new data to update that number.

[magnum lover]

I thought it would average mileage over like the last 10 or so miles driven. Drive smooth or constant and it'll go up but stomp on it a few times or stop and go city driving and you'd see it start going down.

[colsar]

On a somewhat related note, when I'm in the gas-mileage screen and do a reset, 'reset all' shows up - what exactly does 'all' imply?...snip Mike

I've wondered that too!

[KWhale]

Magnum lover and colsar - You may be right about the 10 minutes or so thinking. There is no detailed description of exactly how many minutes the average is for. I've looked high and low to try and find exactly what parameters are being sampled, and how often but so far---nothing. It may be using the data for 5 mins, 10 mins, 30 mins. I do know that it does not calculate the long term MPG you've gotten since the last reset.

Basically the MPG display is a pretty cool thing to see in our cars, but it's not doing what a lot of people think it is, and it's definitely NOT an accurate measure of long term MPG.