I have a 2500 4 x4 dodge diesel the mpg is like 12.5 dose any one know how to figger out the real milage some one told me to add 3 miles to that anyone know on this subject??? its the millage on the roof of the truck the digital read out..THANKS DUSTY

 

Set your odometer take those miles and divide it by how many gallons on fill up, reset each time, my overhead is not even close.

 

how far do u let the truck go empty when u do the math or does it matter

 

It does not matter how much fuel you have in your tank. Next time you fill up make sure you fill all the way and reset your odometer. When you get gas next time divide the miles you drove by the gallons you refill .

 

put gas in a diesel?

 

Take it easy on me I'm a new diesel owner

 

If you are talking tire size affecting spedo, With 35" I would always add 10 percent. I would watch the odometer and it would show .9 for every one mile I actually went. So easy math would be if you went 400 miles. Take 400 X 1.10 which equals 440 miles divided by gallons eqals mpg. That is how I always done it. Hope this helps

 

Best bet is to use a GPS that tells you your mph and the exact number of miles you have driven. Then put an address in it and drive to that address. The further the better. Next, check the difference in your trip mileage versus your odometer. Does that make sense??
Also, when you fill up you need to top it off until you can't put anymore fuel in. Do this before and after the trip. Divide it into the mileage the GPS shows. That's the best way to tell your true mileage...

 

 

Another thing that needs to be kept in perspective...after all the finger pointing and snickering and calling names is done, is that overhead mileage computer calculates using a fixed set of constants. When you change injectors, or tires, or gears, etc. (like was mentioned above), that constant has now been changed and the calc is in error. The pumps, timing, chips, etc. all contribute to the calculation and changing or modifying any of those will create errors in the readout. i.e. changing injectors resulted in higher MPG's just as going the other way would change the readout the other direction.

Also, the mileage is calculated using miles travelled vs fuel left in the tank...so if you idle at the stop light for 5 minutes, watch the MPG drop. If the "running average" has been over the last 600 miles then it won't drop hardly at all, but if the "running average" has been for the last 10 miles, it'll drop several miles in a very short time.

If you fill up and hit the reset, and don't touch it until the next fill up, you will find it is very accurate, BUT... if you say, "Oh, I'm showing 23 on the overhead and I'm out cruising on the highway and getting 23 and hit the reset it'll be the same"...NO it won't. The previous readout was based on many variations of load, time, miles and fuel consumed and starting the overhead over by hitting the reset will begin a new set of calcs based on the upcoming variables.

If you fill up and hit the reset. Then go thru three stop lights just getting to the freeway and then look up when you get up to 60 mph, it'll probably read in the neighborhood of 10-15 mpg, but if you hit the reset and now measure your mileage over the next 50 miles of freeway, it'll be a more accurate representation of your "on the freeway" cruising MPG (but only under those conditions encountered during that specific trip!). The first MPG of say 12 was based on you travelling say 1/2 to 3/4 of a mile and sitting at the stop light for the 8 minutes or so. That initial 1/2 to 3/4 of a mile will not enter into the overall 50 mile calculation even though your fuel is gone! The bottom line is clarification... If I say I get 26-28 out crusing on the freeway at 55 mph...it means I hit the reset at that speed, allowed it to accumulate over a set mileage distance and without any stops or reasons to use excessive amounts of fuel, like passing someone, or bucking a headwind of 30 mph!, I was able to use fuel in an amount that gave me those mpg figures. It DOES NOT mean my truck gets 26-28 mpg all over town, hammering the throttle when I go thru underpasses to hear the stacks snort! LoL
It is very accurate, but only based on the constants and averages it figures.

So, for the most part. We ALL get lousy mileage 'playing' with our CTD's. That's a fact of life and ego. We also ALL will get better mileage if measured the same way and in the proper manner and realize that our variables are entering into the calculation every time we step on the throttle, either in the positiove or negative direction. So, unless you go into the ECM where the MPG calculation is stored and change the constants to match your situation of changes to the truck, you will never get an accurate mileage figure based on those changes. Keep in mind the result is based on miles travelled, amount of fuel used and the time it takes to get those miles. Less time, more fuel, same miles. More time, less fuel, same miles.
yes, it is really simple math but the playing field and the rules seem to change quite a bit from player to player.



db

 

good post cdenny...I also found that the overhead reading was not the most accurate because of things like idle time at stoplights etc...i do find it to be a good guide of high or low mpg on the realtime setting, say when traveling on the hwy or city and trying to keep RPM in a certain range (like on the hwy between 1400 and 1900 to get optimal mpg balancing around 65mph)