# DIC v/s The Math



## XtremeRevolution (Jan 19, 2012)

Simply put, the DIC is consistently too optimistic. The occasions where people exceed the fuel economy reported by the DIC are rare. Every tank of gas I've pumped for the last 29k miles has been 10% too optimistic. Not a single exception. 

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## 70AARCUDA (Nov 14, 2010)

...our DIC numbers average about *7%* too optimistic versus pump & pencil numbers about *95%* of the time...which includes variables such as: different gas stations, different people, different towns, etc..


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## cruze01 (Mar 25, 2011)

Same here but mine has seemed to gradually go south. For the first 3-4 months that I had my new 2013 it was right on the money 99% of the time. Now however its off by 2-3 MPG 99% of the time! I don't know what went wrong.....


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## giantsnation (Oct 11, 2012)

70AARCUDA said:


> ...our DIC numbers average about *7%* too optimistic versus pump & pencil numbers about *95%* of the time...which includes variables such as: different gas stations, different people, different towns, etc..


Took the words out of my mouth! Mine is ~7% too optimistic but it has gotten been as I drive it (13K miles currently).


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## rescueswimmer (Mar 28, 2013)

Not sure how the rest of the D's are running, but I'm about 1-2% off the DIC with Pen and paper with the first or second click when pumping. This has been pretty accurate over the last 6500k.


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## Blue Angel (Feb 18, 2011)

70AARCUDA said:


> ...our DIC numbers average about *7%* too optimistic versus pump & pencil numbers about *95%* of the time...which includes variables such as: different gas stations, different people, different towns, etc..


Put me in this club as well. I use 7% to correct mine as well. It varies a little here and there, but 7% is a good average so far.

I personally think the fuel pressure regulator keeps fuel at a slightly higher pressure than the DIC was programmed for. AFAIK, the fuel economy is calculated based on injector pulse width, so if the fuel pressure runs a little high the car will consume more fuel than the DIC thinks it will.


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## 2013Cruze (Aug 4, 2012)

DIC might be a little optimistic but it's good enough for me.

Not worth my time to figure my mpg exactly.


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## hawkeye (Mar 31, 2012)

Put me in the camp of an accurate DIC. Over 90% of the time it is accurate. All of my other vehicles have been the same way, and I ALWAYS hand calculate and compare to the DIC. I have a niece with a 2011 1LT and it is consistently accurate, too.


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## McLoki (Apr 28, 2013)

If you click on the fully sig, I have the dic mileage listed in the comments for each fillup. Usually optimistic, but not always.

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## Patman (May 7, 2011)

hawkeye said:


> Put me in the camp of an accurate DIC. Over 90% of the time it is accurate. All of my other vehicles have been the same way, and I ALWAYS hand calculate and compare to the DIC. I have a niece with a 2011 1LT and it is consistently accurate, too.



I have an educated answer for this. The 2011 car is old enough and driven enough probably by the same driver/drivers that the onboard computer that does the calculation has learned your driving habits. The DIC is particularly overly optimistic during the first year or @ 20000 - 25000 miles that it is still learning how the driver drives to make an accurate calculation. I noticed my 2012 Eco is getting "closer" with only 10000 miles on it but the longer I drive the car, it will get more accurate. and my 2011 LS with 30000 miles was about accurate. Now that I tuned, it was like a reset for the calculation and it is back to being a bit optimistic esp since I have more boosting going on. 

Given a consistent set of conditions(driving and tuning) it will become more accurate. I compare it to EPA rating seen on the window sticker. People will see and think my car is supposed to get 42 MPG as per the sticker and end up only seeing mid 30s. Problem here the car is new and they are not driving around a track with no traffic, but it is getting withing the range seen in small print. It is just a calculation and marketing! Pull out your pens and paper


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## 99_XC600 (Feb 24, 2013)

McLoki said:


> If you ckick on the fully sig, I have the dic mileage listed in the comments for eack fillup. Usually optimistic, but not always.
> 
> Sent from AutoGuide.com Free App



That's a good tip. I'll need to do the same. So far the DIC has been accurate to .3 from what Fuelly had indicated. Only 2 fill up's so far though.


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## spacedout (Dec 7, 2010)

Patman said:


> I have an educated answer for this. The 2011 car is old enough and driven enough probably by the same driver/drivers that the onboard computer that does the calculation has learned your driving habits.
> 
> Given a consistent set of conditions(driving and tuning) it will become more accurate.


Not true, though I have heard this before. Mine is just as inaccurate at 30,000 miles as it was new. always 2-6mpg high, twice it read 1MPG low both of those times were 100% highway with cruise set at 68-70mph. Mine averages 2.5-3.5mpg high, though lately I have had a few more 6mpg high readings. I have kept track of the DIC readings in the notes on fuelly for every fill up for over a year.


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## spacedout (Dec 7, 2010)

McLoki said:


> If you ckick on the fully sig, I have the dic mileage listed in the comments for eack fillup. Usually optimistic, but not always.


Same here, though I only started doing this about a year ago.


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## obermd (Mar 3, 2012)

When I started hypermiling this past April my car became optimistic by somewhere around 15%. It's now back to 2-5% with an occasional tank clicking off before the "fuel consumed" number in the car.


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## Big Tom (Mar 8, 2011)

For everybody that is so impressed with your DIC, next time you fill up and take 11 gallons and DIC says you used 10, just pay the station for 10 and see how that works.


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## nebojsa (Jan 3, 2011)

I just finished today a trip from St.Petersburg,FL to Kitchener,Ont. About 1400 nm. I always stop at the Flying J /Pilot gas stations along I-75.
I have a issue with the handle that you squeeze. Once you get to the first click it is hard to fill it further.I have to keep playing with it to add more fuel. I know there is more room in the tank,sometimes i can add up to 2 more gallons.

It is hard to calculate the MPG manually if you cant fill it properly or close to full.That might explain why my mileage is all over the place.I have heard also some fill up only to the first click and that is how they calculate MPG. That is great as long all the pumps pump at the same flow rate which i don't think that they do.
Now for the good news... my 2013 Cruze ECO 6 MT with almost 10.000km on it is averaging 5.5 or almost 43 MPG 
I have also used 93,92 octane while in U.S. Love those cheap gas prices


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## McLoki (Apr 28, 2013)

nebojsa said:


> I have a issue with the handle that you squeeze. Once you get to the first click it is hard to fill it further.I have to keep playing with it to add more fuel. I know there is more room in the tank,sometimes i can add up to 2 more gallons.
> 
> It is hard to calculate the MPG manually if you cant fill it properly or close to full.


What I do is turn on the pump so it locks on at the first indent in the handle. (so it fills\shuts off automatically but fills the tank at the slowest speed for that station\pump) when it clicks off - its done (don't add more even though you can get more in there). That should increase your fill up to fill up consistancy.

I also use a website called Fuelly to enter all my fillups. This allows you to average multiple fillups together to get a more accurate reading of your true MPG (as well as see trends in your mileage). Its free (they also have a phone app so I can enter in the fillup/mileage information using my phone while I am at the station and thinking about it)

Good Luck, 

Michael


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## diesel (Jun 8, 2013)

I have checked the DIC several times and found it to always be slightly pessimistic. Generally it shows 1/2 to 1MPG worse than manual calculation at the same pump.


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