What's new
By:
Ram Heavy Duty Forum

Register a free account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members through your own private inbox!

Vehicle MPG gauge

jsalbre said:
Unfortunately it’s not that simple. There are things on cars that are very different from boats (aside from the wheels!). If you really want to know more reasons why, read this Car and Driver article.
Click to expand...

All of those factors apply to every engine, boats, cars, aircraft and aircraft and boat fuel flow and mileage is 100% accurate. Even more so, the surfaces they operate in move. Something that doesn’t happen with a car.

Also, cars are ALWAYS optimistic. That isn’t random.


Sent from my iPhone using Tapatalk
 
RB18C said:
Is anyone else’s MPG gauge always off? I track my MPG on fuelly and my trucks gauge is anywhere from 1-2 mpg off. Think they do this on purpose to make ppl think they are getting better gas mileage? Haha
Click to expand...


Something I noticed yesterday which sort of annoyed me : I keep one odometer for mileage for a "all time" until the day I accidentally reset it. I thought it would be cool to know the average mileage on the vehicle over long periods of time. Currently I have about 5500 miles on the truck and on that odometer. Unless I made a mistake the actual mileage displayed on that long running odometer is completely irrelevant to that goal. It pretty much matches whatever mileage I am registering on fuel economy screen. I would have thought that I could keep a running average, but there appears to be no way to do that. Maintaining that odometer now seems pointless.
 
brucie said:
Something I noticed yesterday which sort of annoyed me : I keep one odometer for mileage for a "all time" until the day I accidentally reset it. I thought it would be cool to know the average mileage on the vehicle over long periods of time. Currently I have about 5500 miles on the truck and on that odometer. Unless I made a mistake the actual mileage displayed on that long running odometer is completely irrelevant to that goal. It pretty much matches whatever mileage I am registering on fuel economy screen. I would have thought that I could keep a running average, but there appears to be no way to do that. Maintaining that odometer now seems pointless.
Click to expand...

The fuel economy screen has its own reset. If it hasn’t been reset for the same time as that second odometer then they will definitely measure the same.

You actually have three separate economy measurements in the display. Two for the trip odometers and one for the fuel economy display.


Sent from my iPhone using Tapatalk
 
Marshfly said:
The fuel economy screen has its own reset. If it hasn’t been reset for the same time as that second odometer then they will definitely measure the same.

You actually have three separate economy measurements in the display. Two for the trip odometers and one for the fuel economy display.


Sent from my iPhone using Tapatalk
Click to expand...

I reset the fuel economy screen every fill. Last night on a 45 mile drive my mileage went up .5 mpg on a trip computer with 5500 miles. That’s mathematically impossible at 15-18 mpg on the trip.


Sent from my iPhone using Tapatalk
 
Last edited:
Marshfly said:
What does that matter? Tank volume doesn’t change.


Sent from my iPhone using Tapatalk
Click to expand...

Plastic tanks actually do expand and contract quite a bit with temperature changes.
 
brucie said:
I reset the fuel economy screen every fill. Last night on a 45 mile drive my mileage went up .5 mpg on a trip computer with 5500 miles. That’s mathematically impossible at 15-18 mpg on the trip.


Sent from my iPhone using Tapatalk
Click to expand...


The MPG systems do not record indefinitely over time, they record some recent chunk of history and automatically replace older data with new. Think of a dash camera that has a 64GB mSD card installed, it may fit the latest 20 hours of driving time on the card, so once that card is populated with data, the oldest data is being re-written with new. That same concept is in play with your MPG screens. Weather you reset manually or not, they are going to eventually catch up to your current driving conditions since they are becoming more current in respect to data as you travel.

The difference between the trip A, trip B and economy display is that each can be manually re-zeroed at your desire. But if all are reset at different times and then ignored for extended time, all 3 will level out to the same data set and results as eventually all will be repopulated with the same historical data.
 
Lary0071 said:
The MPG systems do not record indefinitely over time, they record some recent chunk of history and automatically replace older data with new. Think of a dash camera that has a 64GB mSD card installed, it may fit the latest 20 hours of driving time on the card, so once that card is populated with data, the oldest data is being re-written with new. That same concept is in play with your MPG screens. Weather you reset manually or not, they are going to eventually catch up to your current driving conditions since they are becoming more current in respect to data as you travel.

The difference between the trip A, trip B and economy display is that each can be manually re-zeroed at your desire. But if all are reset at different times and then ignored for extended time, all 3 will level out to the same data set and results as eventually all will be repopulated with the same historical data.
Click to expand...
That's an explanation that makes sense given the observed behavior of the two trip computers. Thanks. It sort of sucks though. How many bits of information does it take to keep a running average? How do you know the info you are getting is accurate when you have no idea how far it goes back. For instance, suppose I take the truck cross country and want a fuel mileage average for the whole trip. You are saying (and I believe you from what I have seen) that that might not be possible. There is no point in measuring anything but miles in those trip computers then.

Edit: Thinking more about your reply, I am still confused. How much historical data do they keep? For my average mileage to go up by .5 mpg over 45 miles, it can't be a heck of a lot. This seems more like a software bug than a lack of capacity to store data.
 
Last edited:
jsalbre said:
Plastic tanks actually do expand and contract quite a bit with temperature changes.
Click to expand...

Quite a bit or negligibly? You aren’t talking about more than a 1% change in actual volume or they wouldn’t fit the mounts. Bulging does not actually change the volume by the way. It just rounds off the corners.


Sent from my iPhone using Tapatalk
 
Let’s look at this from the manufacturers point of view.

Do you really think that they are not going to fudge the display positively to make people feel good about their purchase? They are under no regulation that says it has to be accurate.

All you guys arguing that it is actually somehow accurate but all these other random factors cause the variance are kidding yourself.

Have you ever, in any car, saw it consistently lower than actual? No. That means it’s intentional.


Sent from my iPhone using Tapatalk
 
Marshfly said:
Let’s look at this from the manufacturers point of view.

Do you really think that they are not going to fudge the display positively to make people feel good about their purchase? They are under no regulation that says it has to be accurate.

All you guys arguing that it is actually somehow accurate but all these other random factors cause the variance are kidding yourself.

Have you ever, in any car, saw it consistently lower than actual? No. That means it’s intentional.


Sent from my iPhone using Tapatalk
Click to expand...
My 2500 isn't that far off, but yes you have a point that it is odd that almost every vehicle out there reports better mileage than is being experienced. First thing I did when test driving the 2500 6.4 was reset the mileage and watch the mileage as I drove around in city traffic. Last thing they would want is it reporting worse than reality mileage. I don't think they are so much trying to make people feel good as trying to keep people from feeling bad and making appointments to deal with non-problems of poor mileage.
 
brucie said:
That's an explanation that makes sense given the observed behavior of the two trip computers. Thanks. It sort of sucks though. How many bits of information does it take to keep a running average? How do you know the info you are getting is accurate when you have no idea how far it goes back. For instance, suppose I take the truck cross country and want a fuel mileage average for the whole trip. You are saying (and I believe you from what I have seen) that that might not be possible. There is no point in measuring anything but miles in those trip computers then.

Edit: Thinking more about your reply, I am still confused. How much historical data do they keep? For my average mileage to go up by .5 mpg over 45 miles, it can't be a heck of a lot. This seems more like a software bug than a lack of capacity to store data.
Click to expand...


Looks like a previous 200 mile rolling average.

www.ram1500diesel.com

M.p.g. calculated history average

I have a 15 tradesman ecodiesel. I bought it with 9k and have driven 1500 miles. I see that there is a mpg average for trip 1, trip 2 and on fuel economy setting with miles remaining. How are the mpg averages calculated? Are they each separate values from when the trip meter was reset? How far...
www.ram1500diesel.com www.ram1500diesel.com
 
Lary0071 said:
Looks like a previous 200 mile rolling average.

www.ram1500diesel.com

M.p.g. calculated history average

I have a 15 tradesman ecodiesel. I bought it with 9k and have driven 1500 miles. I see that there is a mpg average for trip 1, trip 2 and on fuel economy setting with miles remaining. How are the mpg averages calculated? Are they each separate values from when the trip meter was reset? How far...
www.ram1500diesel.com www.ram1500diesel.com
Click to expand...
Excellent find, Larry! Thank you, as this was bugging me as well. I was starting to think either it was broken or I was somehow resetting them all.
 
Gondul said:
EPA MPG is generated in a controlled environment under a very specific set of conditions...the likes of which the vast majority of consumers will never experience.
Click to expand...
That statement literally has absolutely nothing to do with the entire conversation going on here.

We're not talking about epa-rated fuel economy at all.

We are talking about the DIC, or driver's information center reported fuel economy based off of the input parameters from the engine management system. So the topic of conversation here is DIC reported fuel economy versus actual hand calculated fuel economy (resetting a trip odometer, and refilling the tank completely full, then driving out the tank and recording both the gallons required refill as well as the total miles driven to have that need of fuel. then taking total miles driven and divided by the amount of gallons that talk to refill gives the actual hand calculated miles per gallon.). besides, there is no such thing as an EPA reported fuel economy for heavy duty trucks in the 3/4 or 1 ton class. That is for 1/2 ton trucks and below it's going all the way down to your tiniest sub compact vehicle or hybrid.

Sent from my SM-N960U using Tapatalk
 
You must log in or register to reply here.
Back
Top