[hobokencentral]

Good day to everyone! I love the Power Flow graphic/ info on the touchscreen but am curious as to how accurate it is. I am still on my first tank of gas, so have not had the chance to refill and test the accuracy. When I had my Subaru Impreza 2015, the digital mpg readout was usually 2-3 mpg higher than my personal calculations. Thus, have any of you been able to compare what the touchscreen displays versus your calculation(s) at the pump?

 

[hobokencentral]

Hey fellow Insight owners...quick update. I have noticed with the last couple of fillups that the discrepancy between indicated and actual mpg numbers has gotten closer. The mpg indicator within the car/ infotainment screen is now approx. only .4 mpg less than the actual, manually calculated mpg. During most of the fillups with my car (since late July), the indicator was underestimating by 1.5-2 mpg. I wonder if - eventually - the mpg indicator will permanently swing toward overestimating the mpg number???!!!

 

[hasarad]

Hey fellow Insight owners...quick update. I have noticed with the last couple of fillups that the discrepancy between indicated and actual mpg numbers has gotten closer. The mpg indicator within the car/ infotainment screen is now approx. only .4 mpg less than the actual, manually calculated mpg. During most of the fillups with my car (since late July), the indicator was underestimating by 1.5-2 mpg. I wonder if - eventually - the mpg indicator will permanently swing toward overestimating the mpg number???!!!

I have nearly the same observation. I've been keeping a spreadsheet. I believe, since the gas tank is on the smaller side, the amount put in varies greater in terms of percentage of over/under-fill. After 5K miles, I'm within about a half a MPG. Don't mind the colors, I just formatted it to show me the outliers (purple= greater than 65mpg). There are two tanks, one at 55mpg and one at 74mpg. This was due to a very slow gas pump which put in more fuel than normal (resulting in 55mpg) and the subsequent tank which made up the difference by using the excess fuel (74mpg). IMO, the on-board MPG indicator is close enough for government work.

 

[hobokencentral]

vehicle mpg accuracy???

Am wondering about the experiences of you all related to the following issue: When I purchased the vehicle back in July, the car displayed a mpg estimate that was approximately 1.5 mpg HIGHER than the actual amount that I calculated when fuelling up (to full). Since the summertime, the mpg estimate and actual amounts have gotten closer to even. At my most recent filling up several days ago, the car displayed a mpg estimate that was approximately .5 mpg LOWER than the actual amount that I calculated. I am now surprised that the trend is reversing. For those of you keeping track, are you seeing a similar situation?

 

[mgldan]

It doesn't take that much to change your MPG calculation by 0.5 MPG. I just filled up on my way home. I had driven 352 miles, and the pump stopped at 8.1 gallons of gas. That's 43.5 MPG. But then the gas station guy did one quick squeeze, and I paid for 8.2 gallons. That's 42.9 MPG, or a 0.6 MPG difference.

The gas pump stops when a certain vapor pressure is reached, and I'm sure's some safe tolerance built in around that so you don't overfill. So the tank definitely has different volumes even when it's "full".

 

[hobokencentral]

It doesn't take that much to change your MPG calculation by 0.5 MPG. I just filled up on my way home. I had driven 352 miles, and the pump stopped at 8.1 gallons of gas. That's 43.5 MPG. But then the gas station guy did one quick squeeze, and I paid for 8.2 gallons. That's 42.9 MPG, or a 0.6 MPG difference.

The gas pump stops when a certain vapor pressure is reached, and I'm sure's some safe tolerance built in around that so you don't overfill. So the tank definitely has different volumes even when it's "full".

That's some really good "insight" mgldan. Since I have bought the car (and live in NJ), I have been lucky enough to go to the same gas station and have attendants who never add that extra squeeze of gas at the end. Thus, it has me thinking of whether something else is manipulating the car's computer (calculations). I normally fill up with three or four - digital - bars left in the gas tank. I always fill it to the top. Not sure what else it could be?

 

[hasarad]

With so little gas (relatively) going into the tank at fill-up, a tenth of a gallon makes a big difference. The only true way to review the on-board mpg indicator is over several tanks. Over the last 7K miles, it's within a half a mpg of actual mileage for me.

I once visited a VERY slow gas pump which put in almost an extra gallon of gas (over what I had expected). That resulted in an actual 54 mpg tank followed by an actual 74 mpg tank (unrealistic). The indicated average was (correctly) right around 64 mpg for both tanks. Things such as fill speed, pump sensitivity and an extra squeeze by the attendant (for those of us in NJ and OR) can make a significant difference.

Since my actual and indicated are only a half mpg apart, I'd say the on-board indicated mpg numbers are about as close to correct as you can get.

 

[Min Pin]

One friend of mine who is in the oil industry told me one time that temperature of fuel makes a big difference in volume pumped. He says to always go to a gas station in the morning when the ground is coldest and get the best volume for the money.

https://www.consumerwatchdog.org/resources/DPReportHotFuelUSAJune07.pdf

 

[hasarad]

One friend of mine who is in the oil industry told me one time that temperature of fuel makes a big difference in volume pumped. He says to always go to a gas station in the morning when the ground is coldest and get the best volume for the money.

https://www.consumerwatchdog.org/resources/DPReportHotFuelUSAJune07.pdf

Due to the depth underground that fuel is stored, the temperature is relatively constant.

 

[dr_glenn]

I too record my fillups and calculate MPG for the last tank. It's close enough (within 1 MPG) to the numbers calculated by the car (I usually use the B tripmeter for each tank, and reset A whenever I feel like it).

I've got a puzzle about the in-car calculations. When you reset a tripmeter, it calculates MPG just for that meter. When you start the car, the center console power flow display resets and then displays MPG for "Current Drive". So, if you start your car and immediately reset trip A, then the two MPG numbers should be the same, correct? For me, they're usually with 0.2 of each other in that circumstance.

This morning I reset trip A after I had traveled about 200 feet (downhill). I then drove 6 miles and stopped for coffee. At that point tripmeter A indicated 51.2 MPG, but the power flow current drive indicated 48.7 MPG.
I can't make sense of this! Tripmeter missed the first 200 feet only, and that was downhill, so any difference should have been minuscule, and A should have actually been less.

 

[hasarad]

I too record my fillups and calculate MPG for the last tank. It's close enough (within 1 MPG) to the numbers calculated by the car (I usually use the B tripmeter for each tank, and reset A whenever I feel like it).

I've got a puzzle about the in-car calculations. When you reset a tripmeter, it calculates MPG just for that meter. When you start the car, the center console power flow display resets and then displays MPG for "Current Drive". So, if you start your car and immediately reset trip A, then the two MPG numbers should be the same, correct? For me, they're usually with 0.2 of each other in that circumstance.

This morning I reset trip A after I had traveled about 200 feet (downhill). I then drove 6 miles and stopped for coffee. At that point tripmeter A indicated 51.2 MPG, but the power flow current drive indicated 48.7 MPG.
I can't make sense of this! Tripmeter missed the first 200 feet only, and that was downhill, so any difference should have been minuscule, and A should have actually been less.

I have my B meter reset for each tank, and my A meter for each drive. So far, A has always matched the current drive. Don't forget, the trip calculates how much fuel was used regardless of distance. If you reset the A meter after 200 feet, the engine may had been running that long. Also factor in any idling before the drive that was removed when you reset the meter (back to zero). Try setting the A meter to reset for each drive. Your numbers should jive then.

 

[hobokencentral]

I have my B meter reset for each tank, and my A meter for each drive. So far, A has always matched the current drive. Don't forget, the trip calculates how much fuel was used regardless of distance. If you reset the A meter after 200 feet, the engine may had been running that long. Also factor in any idling before the drive that was removed when you reset the meter (back to zero). Try setting the A meter to reset for each drive. Your numbers should jive then.

Hasarad, thanks for the advice. I do travel about 80-100 feet away from the pump before I park and reset my trip computer. I will have to think about using both the trip A and B meters rather than just alternating between the two. With my last fillup the other day, the computer is now overestimating the actual mpg by nearly 1 mpg.

 

[Moviemike]

For my gen2 Insight, the trip computer was routinely 3mpg ABOVE the gas pump/odometer mpg numbers. Here in Or. the extra gas above the auto turn-off, or less gas due to placement of the nozzle, or a shift from less gas to extra gas, makes a huge difference. As little as 1.5 mpg above, to as much as 4.5mpg above. This leads to a sine wave pattern on the fuelly.com graph of many fill ups. A series of fill ups very close to exactly the same fillup point, leads to a relatively flat line with relatively small changes due to changing conditions, driving style adjustments, etc. Also, as the car got older the spread between those numbers got worse. Around 1.5 mpg above when new, to around 3 mpg as the odometer passed around 20k.


For my current Civic Hybrid. The spread was 1 mpg when new, but currently its been 0 to 2.2 mpg. Currently 33,815 on the odometer.

 

[hasarad]

Hasarad, thanks for the advice. I do travel about 80-100 feet away from the pump before I park and reset my trip computer. I will have to think about using both the trip A and B meters rather than just alternating between the two. With my last fillup the other day, the computer is now overestimating the actual mpg by nearly 1 mpg.

It all boils down to how much fuel is put in the tank at fill-up. Since we rarely put in more than 7-8 gallons, even a small amount would cause the indicated number to be off quite a bit. I use the indicated number only to show me how well I'm driving effectively. I shoot for a 60-mpg average on my round trip to/from work (100 miles). Garaging the car in winter has helped me to get close to this goal.

 

[Wolverine51]

"Avg MPG" shown on dashboard

When I'm looking at Trip A on my dashboard, at the Avg Fuel mpg number, I don't understand why that number can sometimes change so much in a small amount of time. In order for the "average" to change, it seems to me that it should take more time. Is my question clear?

 

[sEXzNsite]

When I'm looking at Trip A on my dashboard, at the Avg Fuel mpg number, I don't understand why that number can sometimes change so much in a small amount of time. In order for the "average" to change, it seems to me that it should take more time. Is my question clear?

My thought is since the TRIP mileage is cumulative it will take whatever the "Current Drive" numbers are and recalculate them into the average. I'm just wondering if the computer is basing all its calculations on ACTUAL FUEL USED against TOTAL MILES DRIVEN. If one is able to drive their car in EV a good amount it will certainly boost the MPG and its average. Basically racking miles in EV is simply ADDITIONAL MILES WITH NO FUEL USED. That's just my hyporthetical analysis :wink:

 

[mgldan]

When I'm looking at Trip A on my dashboard, at the Avg Fuel mpg number, I don't understand why that number can sometimes change so much in a small amount of time. In order for the "average" to change, it seems to me that it should take more time. Is my question clear?

The average should change quickly when you're early in the trip gauge (say, within the first 5 miles) and change slowly when you're deep into it (say, 400 miles in, when you're close to needing to fill up).

Personally, I use the Trip A meter to track my current day (manually reset, since I may turn the car off and on several times a day) and the Trip B meter to track my current tank (which can auto reset through a setting on the Display Audio).

 

[kasparguy]

trip computer accuracy

Has anyone else noticed the trip computer consistently under rating the mpg? I've been topping off the tank around every hundred miles (give or take a few) and the mpg I get calculating the miles on the trip meter divided by the number of gallons it take to o top off is usually a couple mpg higher than what the trip computer says. I've been consistently 49.something where the computer says 47. or at best 48.


I should probably not top off the tank after so few miles. But right now, being summer, I'm not driving nearly as much as I do/will during the school year. And if I waited until my tank was significantly lower I'd forget how to use a gas station! :grin:

 

[insightfully]

Has anyone else noticed the trip computer consistently under rating the mpg? I've been topping off the tank around every hundred miles (give or take a few) and the mpg I get calculating the miles on the trip meter divided by the number of gallons it take to o top off is usually a couple mpg higher than what the trip computer says. I've been consistently 49.something where the computer says 47. or at best 48.

I should probably not top off the tank after so few miles. But right now, being summer, I'm not driving nearly as much as I do/will during the school year. And if I waited until my tank was significantly lower I'd forget how to use a gas station! :grin:

...added your question to this existing thread on "Vehicle MPG Accuracy" as there are some related comments/discussion that may help answer your question.

There are varying reports of the calculation being over/under actual (posts 1, 7, 11). Pump variability can also factor into mpg calculation differences (posts 2, 4, 12), amplified due to the relatively 'small' volume held in the Insight's gas tank.

 

[kitguyy]

MPG discrepancy

Just logged my first fuelly and the MPG came out to be much better than what the car is reporting 57 vs 50. I've tracked it since the last fuel up and fueled up half a tank which should suffice for a good estimate. Is this a common or a known thing?
Thanks!