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Discussion Starter · #1 ·
Now for starters, this is strictly an OPINION and I open the floor for debate so let's hear some other opinions!

OK so I have a theory on why your DIC may be more accurate than you think, and maybe more accurate than hand calculations at the pump. My basis for this is, as always, margin of error. with a car that gets such good MPG being off just a little on your calculations can skew numbers quite a bit. I am assuming most of you reset the DIC at each tankful, like I used to. I have noticed the longer you let it go the more accurate it becomes when compared to calculating by hand, which makes sense because the margin of error by hand will tend to "average out" over longer periods of time.

My 2 biggest concerns with hand calculation are that when you go to fill the tank you have no idea how much fuel is in there before you fill up, so that means at the end of that tank you really have no idea how much fuel you used. Throw in the addition of even if you use the same pump and fill to 1 click the odds are pretty good that there is a different amount of fuel in the tank than the precious fill up. So realistically, if you drained the tank completely, pumped in a known quantity of fuel, drove it, then emptied the tank again to see what was left you would be spot on. But for giggles here is an example, lets say you pump in exactly 10 gallons of gas and went 400 miles, piece of cake 40 MPG. Now if you figure that maybe between not knowing what is in the tank and margin of error at the pump that you used just 1 more gallon of fuel. That drops your MPG to 36 and change, so just one gallon of fuel off gives you a margin of error of almost 4 MPG. Now if you average that over say, 5000 miles, the variances over and under will roughly average out.

Now to the DIC, which, with the exception of variances in tire diameter due to air pressure, etc, knows exactly how much fuel it has used over what distance. Runs a very simple math equation and spits out the number. I'm willing to bet over any meaningful period of time the DIC is gonna give you closer to real world mileage than calculating by hand.

Thoughts?
 

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that makes no sense.

you drive x number of miles. you put y number of gallons in to fill it up. your mileage is x/y. sure it might vary a little from fill to fill but over time it is going to be extremely accurate.
 

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...refill the tank to the same point every time (ie: ONE-click) and you have the quantity of fuel consumed, the gallons you put INTO the tank.

...also, LONG-term "averages" (many miles and multiple gallons) tend to be more accurate than SHORT-term "averages" accumulated between fuel pulse injections.
 

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It will be pretty close. Though the DIC may overestimate at times simply because it is not 100% accurate in calculating the amount of fuel you use under high load conditions. I notice that even over really long tanks, the more highway driving I do under cruise control, the more accurate the reading is. It is also more and more accurate in fair weather.. meaning in winter my DIC was no where in the ball park and now it seems spot on because temps are 60ish.
 

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Discussion Starter · #6 ·
What I am saying is how do you know it is the same point every time? Do you assume that 1 click is exactly the same point every time? Only takes about 1 second to pump an extra 1/4 gallon into the tank. My point is the only "known" quantity you have is what you pumped in. If you burned EXACTLY what you pumped in than yes it is accurate, but I highly doubt you fill the tank to the same spot every time
 

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Would fuel being in the fuel lines pump and filter wouldnt that make a change too or not.

h3llion
 

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Discussion Starter · #9 ·

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I'm getting a headache,,, put fuel in, drive, and be happy it don't cost you as much as your last car did. :th_coolio: J/K

I to, wonder how accurate the DIC can be,,,but as long as I'm getting over 30,,, I'm saving $120 a month @ $4 per gallon.

Fuelly will help where the DIC lacks or over guesstimates.
 

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You really want me to do some math after a hard day at work, don't you? I'd probably do it, but my wife took the Cruze, and it has all my gas receipts in it. I'll have to ask if she likes it better than her Equinox when she gets back. :th_coolio:
Let us know.:eek:fftopic:
 

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I havent' checked my Cruze's DIC, but if it's like my Montana's, the only time it will be even close is during long open road trips. Accelerating from stop lights and signs seems to be the biggest culprit for the DIC's underestimation of fuel used.
 

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What I am saying is how do you know it is the same point every time? Do you assume that 1 click is exactly the same point every time? Only takes about 1 second to pump an extra 1/4 gallon into the tank. My point is the only "known" quantity you have is what you pumped in. If you burned EXACTLY what you pumped in than yes it is accurate, but I highly doubt you fill the tank to the same spot every time
there is no doubt that one tank can be off quite a bit but it will average itself out over a few tanks. it's not like you can put an extra 1/2 gallon in there every tank.
 

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I'm with NBrehm. I am not saying the DIC is 100% dead on accurate. There are going to be a lot more variables that can affect one's calculations than there are going to be for the DIC.

Another variable that I think could affect your calculations is the temp outside when you top off your tank. During this time of the year in WI it is not completely out of the ordinary for it to be in the 70's one day and in the 30's the next. Lets say you top off your tank on a 70 degree day and then the next time you top off your tank it is 30 degrees. The gas left in the tank is going to take up less space than it would on another 70 degree day causing you to put in more gas. The more gas left in the tank the more of an effect it will have. Might not be a large difference but still a difference.

Also like UpstateNYBill said, if the pavement at the pump is not perfectly level it will alter when the pump will click. You are not going to be able to park your car in the exact same spot. Might not be a large difference but little variations can start to add up.

Just my two cents
 

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I have been using an app called fuel log on my phone. When you fill up, you enter the price you bought the fuel for, the exact number of gallons you put in the tank and the current odometer reading. The app then calculates the MPG for that particular tank and logs it. I reset the DIC every time I fill up and find it is always about 2-4 MPG higher than the actual MPG. Maybe I will let it roll for a couple tanks and see if it gets any closer.

Check out the app (I have android and am not sure if it is available for apple as I absolutely despise ANYTHING apple. No offense to anybody). It does a lot of neat things like calculating your average fuel cost per day, month, year. It has a calculator function to determine the fuel cost of a road trip based on your average MPG, average fuel cost and trip distance. Definitely a cool app and worth a look. There are free and paid versions.
 

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Discussion Starter · #18 · (Edited)
there is no doubt that one tank can be off quite a bit but it will average itself out over a few tanks. it's not like you can put an extra 1/2 gallon in there every tank.
You could, although not likely. Statistically there will be tanks where you put in less fuel also. But if you keep resetting the DIC you eliminate the old data set and start a new one, which will make it more inaccurate. I agree that the longer you go the more accurate your readings will be both ways. If I do a single tank I normally get around 41MPG on the DIC and roughly 39 by hand. I went and added 10 tanks worth of receipts and let the DIC run for 10 tanks and ended up with 38.2 on the DIC and 38.6 by hand, which makes me fairly sure my combined MPG is about 38. The other thing that happens alot tank by tank if you aren't meticulous is rounding. If you round say, round 38.23 to 38.2 it will add up also
 

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this seems pretty simple to me. there is no way that computer is going to "estimate" your mileage better than hand calculations based on miles traveled and fuel used.

i think the issue here is people are looking at the possibility of putting in a little more or a little less gas on one fill up and thinking that can have a cumulative effect over time when it is really just the opposite. looking at the average of several tanks is going to reduce any filling variances.

gas pumps are temperature compensated. i dont really know how all of that works but i think the reported fuel pumped is pretty accurate.
 

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What kind of difference is everyone seeing on Gallons used? Mine has never been more than 2/10 off compared to the pump. I have actually had quite a few tanks be an exact match. I wish the DIC also had a lifetime mileage like the onstar app does.
 
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