Okay, I know the XZT is a pressure box and the overhead mpg reading will be off. I have had the XZT on my truck since mile 1000 and I have 31000 now. Heres the issue. At first the overhead would see a max of 18.5 mpg without the XZT and 22 mpg MAX with the xzt on the truck. I have hand calculated every single tank of diesel. Combined city/highway is always between 17-18mpg and highway only mileage is close to 20mpg. Could someone explain to me why my overhead mpg has steadily increased over the past 30k mileage yet the mpg has not changed. Right now its showing 26 mpg and getting the same 18 mpg hand calculated. I may have jumbled up my explanation. Long story short...the overhead mileage has steadily increased over the last 30k miles yet hand calculations have not. Is this an indication of a problem?

 

Do you reset it after you fill up?

 

My question also. With my current stack my overhead is between 5-5.5mpg off compared to hand calculated. The variation on my part is how much city/highway mileage. All city it is 5.5mpg off, all highway it is 5 mpg off.

Mine is consistent with this stack. I reset my overhead mpg at every fillup. I can judge very close with my overhead this way.

Of course its too bad it is not the accurate number

 

Turn that overhead crap off, Ive have had my truck for almost 3 years. I havent seen that overhead mileage display since I drove it home from the dealer.
No disrespect intended.

 

my overhead is within .1mpg anytime I have ever done a hand calculation.

 

the overhead mpg computer works on my gran prix...why can't it work on the dodge?

 

Mine is sometimes dead on and sometimes it's 2-2.5 mpg off. That's without the Quad box turned on. It's always at least 1 mpg off with the Quad on. I use it as a measure of my driving style when I'm trying to get better mileage.

 

I reset it with each gas tank. The part I am curious about is how the actual hand calculated MPG can stay the same yet the overhead number can be 25 one week and 26 the next. I hand calculate every single tank and was curious why the correlation isnt close. Like overhead says 25 and hand calculated is 18...giving 7 mpg high. Instead, it said 23 when I first put the XZT on and hand calclulated 18 and now it says 26 and hand calculates 18.

 

I haven't had that big of a difference of 8 but I have had a range from 4-5.5 off from the overhead.