Dic Or Gas Pumps

cghbuilder86 · February 25, 2011

Some may think this is a dumb question but it's been on my mind a lot so here it goes. My DIC average MPG usually shows from .7 to 1.0 MPG better than what my hand calculated numbers show over a tank of gas. I'm wondering which is more accurate? I used to think the hand calculated was more accurate hands down. But then I started thinking about it more. Wouldn't the computer system in todays vehicles be pretty advanced for measuring gas used? When I filled up today The pump showed that my truck held 19 gallons where the DIC showed that I had only used 18 gallons since the last fill up. They should be the same. So is it the gas pumps that are off or my DIC? Probably the DIC I guess. Hard to believe that the gas pump could be off by as much as 1 gallon out of a 20 gallon fill.

Just thought I would get some input on it. I tried to do some research on gas pump accuracy. It does look like they can be inaccurate because of expansion and contraction and all...probably not off by this much though. I couldn't find any numbers on how much they can actually be off though. Anybody?

cghbuilder86 · February 25, 2011

I guess that would make each gallon off by about .052 Is that possible?

old-chevy-dude · February 25, 2011

check the sticker on the pumps. They are supposed to be calibrated by the Dept of Weights and Measures yearly.. I've seen some that have 3 year old stickers on them, no new calibrations.. I refuse to buy gas there.

our local news station just did a huge report on this last week, they followed along with a Dept of Weights and Measures tester to 40 gas stations and found that over 70% of the pumps were off by 5% or more, meaning that you are being charged for a gallon of gas but actually only getting 95% of a gallon, the diesel pumps were the worst being off by as much as 25%

cghbuilder86 · February 26, 2011

where would this sticker be?

old-chevy-dude · February 26, 2011

on the pumps.. usually the Dept. of Weights and Measures is a sub division of the local county Dept. of Food and Agriculture. But the sticker should be on the pump in a place you can easily find it.

MikeNH · February 26, 2011

Every vehicle I've owned that had a trip computer the vehicle read a bit higher than the hand calculations. I always went with the calculated numbers.

Stevens03 · February 26, 2011

I've noticed a local station amount of fuel used was consistently higher than what the truck reported. I started going to another station which seemed to be much closer to what the DIC reported. I think as mentioned above, the pumps calibration could be off. What angers me is most times it's in "their" favor and not yours when things are wrong.

Either way, hand calc should be most accurate since it's basically mileage driven against gallons used.

tanked_darren · February 26, 2011

My truck is consistently about 4-5 liters off when I fill up, (according to liters used) DIC

That works out to about your 1 gallon your missing between fillups. I would like to think the pump method is more accurate but who knows, I have no idea how a vehicle computer works in the way of measuring fuel used.

EDIT: Gas pumps can be unaccurate they're supposed to have certification stickers but I've seen em out of date, once in awhile the news reports inaccuracys in gas pumps usually during gas price spikes.

SparkySparks · February 26, 2011

I think both the DIC and the pump can be off a little, depending on how well the pump is maintained. I use the DIC calculations and I do it by hand also using the pump and then average the two.