Dash calculated fuel consumption average vs hand calculated average

[TRAMPLINEMAN]

I was wondering if any of you compare the two on your trucks and if they're close or a long way off. I've never filled the truck from a station pump so I can't get an accurate gallon count.

 

[garrettg84]

My dash calculated is actually pretty good. The only problem is that it is averaging over a shorter timespan than my tank of gas. If we we could simply 'reset' the calc every time we fill up and force it to simply display the number of miles driven divided by gallons used, it would be a perfect hand calculated measurement every time. But for some stupid reason the engineers thought it necessary to do this measurement over some arbitrary shorter timespan. Really, wtf engineers?

Basically, if your driving habits are consistent and the terrain/load is consistent over the life of a tank, then your mileage calc will be accurate. If you do a lot of spirited driving or driving loaded in a city up front, then pop out on a highway for the last bit of a tank, your mpg calc will register much higher because it is calculating over the more recent time span. If you do it the other way around with better mpg highway and finish a tank driving loaded in a city with traffic, your mpg calc will actually register lower than hand calc.

Basically, the truck computer is perfect. But it is only perfect over the arbitrary number of miles that are stored in it's memory. People who say it is inaccurate either don't understand the technology or their truck is severely broken.

The test - if you want to know for sure. Fill up your tank, reset your mpg meter in your dash. Drive for 50 or so miles round trip(I don't think it averages over less than 50 miles but am not convinced it does much more than this). Refill your tank. Hand calc it, compare.

 

[Sikos]

Tramplineman,
I track all my fill ups. I built an excel spreadsheet that tracks total mileage, trip mileage, cost of fuel, truck computer mpg and actual mpg.
Both the 2011 Ram & the 2015 Ram are close. Usually less than 1/2 mpg difference where as our 2013 GMC Terrain is approximately 2 mpg different.
Joe

 

[RikDavis]

Tramplineman,
I track all my fill ups. I built an excel spreadsheet that tracks total mileage, trip mileage, cost of fuel, truck computer mpg and actual mpg.
Both the 2011 Ram & the 2015 Ram are close. Usually less than 1/2 mpg difference where as our 2013 GMC Terrain is approximately 2 mpg different.
Joe

I also track mine in excel spreadsheets. I find the EVIC is consistently 1 to 4 miles higher than the actual use. I am a gentle driver and I have always assumed this was tracking from the time I reset. If it does it in smaller chunks perhaps that would explain the difference. The error is noticeable worse when I have a mix of towing and not towing.

I have a feeling the " travel distance left" is either optimistic or I am not brave enough to push it to the limit.
Not at all unhappy with my fuel mileage, but wish the dash indicator was a bit closer

 

[TRAMPLINEMAN]

Thanks a lot for all the info. I was hoping it was close and it sounds like it is. I really can't track my gallons used to fill cause I always fill the truck thru my dual filtered bulk tank and I don't have a gallon counter on it.

 

[Ram4Sam]

After each fill up, I reset the "trip A" and then do a hand calc at the next fill up. The EVIC on my truck consistently shows 1 mpg more than my hand calc figures...... I wish it was the other way around......

Sam

 

[photowrite]

I also track mine in excel spreadsheets. I find the EVIC is consistently 1 to 4 miles higher than the actual use. I am a gentle driver and I have always assumed this was tracking from the time I reset. If it does it in smaller chunks perhaps that would explain the difference. The error is noticeable worse when I have a mix of towing and not towing.

This is very similar to my experience. At every fill-up I reset both the fuel-economy and Trip A meters, and always hand calculate the consumption, including any odometer error for different tires I may have installed. The closest the EVIC MPG reading has been was within a few tenths, but generally it's optimistic enough (1-3 mpg) that I'd call it inaccurate.

I have a feeling the " travel distance left" is either optimistic or I am not brave enough to push it to the limit.
Not at all unhappy with my fuel mileage, but wish the dash indicator was a bit closer.

It seems to be as optimistic as the EVIC/ECM readings... If your EVIC is close for your current driving and tank, then it is likely fairly accurate. But when the two reading diverge the distance-to-empty can be wildly inaccurate. Having run my tank down to where the light comes on a couple times then immediately filling, I know how much fuel remains when the tank is low, as well as my current driving and probable consumption. I use this knowledge and experience to figure my 'final' distance to empty instead of what the ECM/EVIC says.

 

[TRAMPLINEMAN]

The EVIC on my truck consistently shows 1 mpg more than my hand calc figures...... I wish it was the other way around......

Sam

What does your truck and your hand calc usually show? I'd like to compare it to mine.

 

[photowrite]

My dash calculated is actually pretty good. The only problem is that it is averaging over a shorter timespan than my tank of gas. If we we could simply 'reset' the calc every time we fill up and force it to simply display the number of miles driven divided by gallons used, it would be a perfect hand calculated measurement every time. But for some stupid reason the engineers thought it necessary to do this measurement over some arbitrary shorter timespan. Really, wtf engineers?.

I agree with the WTF comment... Every other vehicle I've owned that had some type of ECM MPG readout seemed to calculate for the total period since the last reset. I think the ECM/EVIC might not only sometimes calculate over a shorter timespan, but sometimes a longer timespan using recent past mpg data.

I recently did some back-to-back mpg tests over a 130 miles distance, all freeway. The more 'normal' driving after these test had the EVIC MPG average, as well as the distance to empty (way off!) very optimistic. Instead of using the current usage since the recent reset, the ECM seems to be using the past average which was not even close.

 

[Ram4Sam]

What does your truck and your hand calc usually show? I'd like to compare it to mine.

My usual tank of fuel is roughly 80/20, city/freeway miles, with a short freeway commute. Summer months the evic is usually in the 15.6 to 15.8 mpg range, during the so cal winters, the evic shows in the 14.4 to 14.8 range. My hand calcs are pretty much 1 mpg less........again..... Because of some serious health issues (the wife) I have yet to do any towing of any distance or even a full tank of freeway miles. I'm quite curious of my towing mileage and empty trip mileage but that's going to have to wait a bit.....

Sam

 

[jus2shy]

Over the life of my truck, my EVIC's error from hand-calculation is only 0.61 mpg optimistic. Pretty darn good for any electronic system. I keep everything in an excel sheet like the others, where I also note where the fuel came from in case I ever have a fueling issue.

 

[seafish]

I really can't track my gallons used to fill cause I always fill the truck thru my dual filtered bulk tank and I don't have a gallon counter on it.

COurse if you want to, you could always get one of these…I have used it for several years now on my farm tank with no problems.

https://excel-equipment.com/farm/meters/fuel-meters/fill-rite-in-line-digital-meter.html

 

[Cummins12V98]

Mine is consistently .4 high.

 

[gsbrockman]

Basically, the truck computer is perfect. But it is only perfect over the arbitrary number of miles that are stored in it's memory. People who say it is inaccurate either don't understand the technology or their truck is severely broken.

:-laf Really ????

It's all about miles traveled and gallons consumed.....period.

That's hilarious. As others have mentioned....the EVIC is optimistic a good percentage of the time, and overly optimistic a larger percentage of the time. I've tracked over 4,069 gallons and $15,003 worth of #2 through my 2014 RAM 3500 Crew Cab 4x4 the last 11 months, and the EVIC is way off from hand calculated.

 

[garrettg84]

:-laf Really ????
It's all about miles traveled and gallons consumed.....period.

You glossed right over and didn't bold the actual part of the statement that mattered 'perfect over the arbitrary number of miles that are stored in it's memory.'

It may only be averaging over the last 10 miles. I'm not sure what the arbitrary mileage it is keeping track of over. I can tell you when I'm on the highway on cruise tank to tank, it is spot on (because there is no variation in driving). When I go from half driving in city to half driving on highway (evic shows higher than hand calc) or half highway to half city (evic shows LOWER than hand calc), the latter is the direction my EVIC is weighted as compared to my hand calc. Maybe you don't understand moving averages?

I'd assume most people are refuelling while unloaded between pulling other than the rare stop while hooked up towing across country. You unhook, drive without any load, and on the way to your fuel up, your MPG ratings on your EVIC skyrocket as compared to towing MPG. Then you complain, '[omg] the EVIC is optimistic a good percentage of the time, and overly optimistic a larger percentage of the time.'

Here's some basic reading so you'll understand why it makes a difference:
http://en.wikipedia.org/wiki/Moving_average
http://en.wikipedia.org/wiki/Exponential_smoothing

 

[RikDavis]

I agree with gsbrockman. I believe it is averaging since last reset. One only has to compare how fast the average changes when going up hill or down hill 10 miles after reset as compared to how slowly the average changes after several hundred miles from reset on the same hills .
I have never seen the evic read lower than the hand calculated mileage. I have seen it close a few times but usually off by 2 or more miles per gallon (high). The only real use for this display is to let you know fuel is moving through the system. On my truck it is not accurate enough to take seriously.
I usually use the A odometer when I buy fuel and the B odometer for the whole trip

 

[gsbrockman]

I'd assume most people are refuelling while unloaded between pulling other than the rare stop while hooked up towing across country. You unhook, drive without any load, and on the way to your fuel up, your MPG ratings on your EVIC skyrocket as compared to towing MPG. Then you complain, '[omg] the EVIC is optimistic a good percentage of the time, and overly optimistic a larger percentage of the time.'

All I can add is "assume" = "***" out of "u" and "me"....

Click on my fuelly link. If you hover over each "note" in my 143 fuel ups, you'll most likely find I note ET (elapsed time), average miles per hour, and the overly optimistic EVIC calculated MPG figure for that tank......per "Trip A" and it's reset every fill up. Based on my findings of using "Trip B" over x number of fuel ups on a hauling route (say----5 or 6 fuel ups without resetting Trip B) I can safely say that Trip B is just about a dead on average of the last three Trip A EVIC readings.

http://www.fuelly.com/car/ram/3500/2014/gsbrockman/298756

But......what do I know.....I've only done this for the last 11 months and 60k miles.

MOPAR EVIC's have......and always will be....overly optimistic.

 

[garrettg84]

I agree with gsbrockman. I believe it is averaging since last reset. One only has to compare how fast the average changes when going up hill or down hill 10 miles after reset as compared to how slowly the average changes after several hundred miles from reset on the same hills .
I have never seen the evic read lower than the hand calculated mileage. I have seen it close a few times but usually off by 2 or more miles per gallon (high). The only real use for this display is to let you know fuel is moving through the system. On my truck it is not accurate enough to take seriously.
I usually use the A odometer when I buy fuel and the B odometer for the whole trip

All I can add is "assume" = "***" out of "u" and "me"....

Click on my fuelly link. If you hover over each "note" in my 143 fuel ups, you'll most likely find I note ET (elapsed time), average miles per hour, and the overly optimistic EVIC calculated MPG figure for that tank......per "Trip A" and it's reset every fill up. Based on my findings of using "Trip B" over x number of fuel ups on a hauling route (say----5 or 6 fuel ups without resetting Trip B) I can safely say that Trip B is just about a dead on average of the last three Trip A EVIC readings.

http://www.fuelly.com/car/ram/3500/2014/gsbrockman/298756

But......what do I know.....I've only done this for the last 11 months and 60k miles.

MOPAR EVIC's have......and always will be....overly optimistic.

Absolutely zero chance of it averaging since the last reset. I reset mine about 3000 miles ago and a 5mile trip has the capability of affecting my mileage more than .3 or .4 mpg. Statistical impossibility unless I was actually getting negative mileage or mileage in the hundreds of MPG.

People look for patterns. They often find them in places where there are none.

Correlation != Causation.

100% of shark attacks occur within 1 mile of sand. Sand is clearly the common denominator and causes shark attacks. I guess I should be looking out for sharks in the desert too.

Explain why my EVIC reads LOWER (11.1 MPG, which going to be accurate for my next fuel up - shorter time period) than hand calculated fuelly mileage (12.5) over the last reset period. And no, I've never missed a fill up.

You don't have to be a jackass.

 

[gsbrockman]

Absolutely zero chance of it averaging since the last reset.

I suppose you have access to the computer code that RAM uses for this wonderful EVIC calculation???

You don't have to be a jackass.

Perhaps you should heed your own advice......as I stated before---miles traveled and gallons consumed, folks.

 

[garrettg84]

I suppose you have access to the computer code that RAM uses for this wonderful EVIC calculation???


Perhaps you should heed your own advice......as I stated before---miles traveled and gallons consumed, folks.

No, I can do basic math. Here's the weighted arithmetic to show you why I'm right and you are an idiot. I can go up or down .5mpg in my ~6mi trip to the office.

3000mi at 12.5mpg = 37500
6mi at 80mpg = 480
total 37980 / 3006 = 12.635


Even if I managed to get an impossible 80mpg for the 6 mile trip to work, I only bring the average over 3000miles to 12.6mpg. Now the fact that I can raise and drop my mpg by half a mile per gallon over the distance of 3000 miles within a 6 mile time span means I am right and you are an idiot.

Based on the weight of my 6 miles doing +- .5mpg difference, I'd estimate that the EVIC is averaging over about 35-50 miles worth of a trip. I can't get an exact estimate as my instantaneous mpg varies and my driving habits vary a bit more. See the math below that would confirm why my EVIC can jump up .3-.5mpg in a 6 mile trip.

50mi at 12.5mpg = 625
6mi at 16mpg = 96
total 721/56 = 12.8mpg

30mi at 12.5 = 375
6mi at 16mpg = 96
total 471 = 13mpg

School folks. It makes a difference.