MPG gauge accuracy

[GR_CoB]

Recently got a rental 2015 Nissan Sentra for a family trip. Along with the Sentra took the 2010 Civic from my signature. Filled both cars at the same gas station and the same pump. Sentra had two passengers, roughly 450lb combined, and Civic had four passengers, roughly 850-900lb combined. Both cars were on the same exact route, same exact gas, same exact weather conditions, different loads though. Round-trip was 500 miles. My Civic does not have an MPG readout, but the Sentra showed 42.3 MPG. I got pretty excited with those numbers and when we got to the next gas station I was really anxious to do the math and see how close the cars are in MPG. Again filled up at the same pump. Well, surprisingly for me - both cars came out to a 37.0 MPG... Even though the Civic was much more loaded... I knew the MPG gauge in Sentra is optimistic, but 5.3 MPG?!? The MPG gauge in my Scion xB is always within .5 MPG from the actual math results. The Highlander always manages to be within .5-1.0 MPG. Just out of curiosity - how accurate are the MPG gauges in your vehicles?

 

[racer12306]

I've seen mine be
I don't really understand why they aren't more accurate, they know the pulse width and the miles driven.

 

[Quattro Pete]

Mine is within 1 mpg of hand calculated value. I do have the ability to adjust its accuracy if need be.

 

[bioburner]

My Transit seems pretty close and 2012 Xb is pretty good too. Now things are messed up with changing(Xb) to a bit better and larger tires but can live with better mileage and just have to adjust manually.

 

[ARCOgraphite]

you would need to average your fillups over maybe 7 tanks to get any good data. One data point point could be way off given the variability in filling to same volume. I don't believe the 42 MPG.

How did you like the sentra driving experience. BMW 3 series like?

 

[OneEyeJack]

When I drive the company Prius and check after filling up I'm usually within one or two tenths of a mile per gallon. I'm surprised at how accurate the read out is.

 

[GR_CoB]

I have no problem with doing 7 tanks for data purpose. As long as I get a sponsor for gas and rental.

 

[GR_CoB]

Originally Posted By: ARCOgraphite
BMW 3 series like?

Hah I wish. The rear seats are hard and uncomfortable. But sound insulation is better than the Civic.

 

[supton]

14% error, pretty significant. If it was a car that you actually owned you could "train" your eye to read the fuel gauge, look at the elapsed miles, and be in that level of accuracy.

 

[horse123]

Hand calc is significantly less accurate than the MPG readout in most cars. Pumps shut off at different times, different gas blends foam slightly differently and cause different shut off times as well.


Originally Posted By: ARCOgraphite


How did you like the sentra driving experience. BMW 3 series like?


LOL THAT'S FREAKING HILARIOUS. GOOD JOKE BUDDY.

 

[Tman220]

My 2012 Regal GS is always stays within a .4 MPG swing, its spends equal amounts of time either .2 mpg optimistic or .2 mpg short of hand calculated. I've never owned or seen a car that remains this accurate and consistent. Most computer readouts seem to read varying degrees of too optimistic.

I've never seen one as far off as that sentra though wow.

 

[tomcat27]

I've put 31k on my Sentra, and certainly the car is about 4 mpg optimistic. I get 33 in mixed driving; and anywhere from 37 to 40 depending on the speed limit. (staying in the 65-70 range renders 40) My jeep used to be about 2 mpg optimistic.

 

[mclasser]

My cars are optimistic by 1-2 MPG. I always track my mileage by hand.

 

[SonofJoe]

Over 18,500 miles, driving my little Kia Picanto, the trip computer said I'd averaged 58.3 mpg but in reality, it was closer to about 55.1 mpg.
Over 4,000-ish miles, our little Suzuki Celerio's trip computer says the car has averaged 73.1 mpg but in reality, it's done 70.0.

 

[Ohle_Manezzini]

It's average calc or was setup to zero before the trip?

 

[Nick1994]

Originally Posted By: SonofJoe
Over 18,500 miles, driving my little Kia Picanto, the trip computer said I'd averaged 58.3 mpg but in reality, it was closer to about 55.1 mpg.
Over 4,000-ish miles, our little Suzuki Celerio's trip computer says the car has averaged 73.1 mpg but in reality, it's done 70.0.
Imperial gallons?

 

[horse123]

Originally Posted By: Nick1994
Originally Posted By: SonofJoe
Over 18,500 miles, driving my little Kia Picanto, the trip computer said I'd averaged 58.3 mpg but in reality, it was closer to about 55.1 mpg.
Over 4,000-ish miles, our little Suzuki Celerio's trip computer says the car has averaged 73.1 mpg but in reality, it's done 70.0.
Imperial gallons?


Almost certainly, also remember, in Europe, they have tiny little feather-light cars that have like 1.2L engines in the mid range. In fact that Kia is a few CC under a liter.

 

[barryh]

My cars displayed mpg is very accurate. It's no more than 2% optimistic which I think is impressive.

The other thing which impresses me is the speedo. After 45 years of driving cars with mechanical speedo's that were deliberately designed to grossly over read, my current car is absolutely spot on. It makes driving through speed cameras a more precise affair.

 

[SonofJoe]

Originally Posted By: Nick1994
Originally Posted By: SonofJoe
Over 18,500 miles, driving my little Kia Picanto, the trip computer said I'd averaged 58.3 mpg but in reality, it was closer to about 55.1 mpg.
Over 4,000-ish miles, our little Suzuki Celerio's trip computer says the car has averaged 73.1 mpg but in reality, it's done 70.0.
Imperial gallons?


Yes, sorry, imperial gallons (even though we no longer have an empire!)

Both the Picanto and Celerio have 1.0L, 3 cylinder, normally aspirated petrol engines. Considering the similarity of the two cars, I was amazed at the difference in fuel economy I saw but it's sort of logical. The Suzuki is lighter (kerb weight 840 kg), has a higher VI compression ratio engine (11:1) and uses 0W20 oil as standard. Interestingly it's also an automatic (albeit the robotised manual sort).

I've been so impressed by the wife's Celerio that I've just traded the Kia in to buy myself a one.

 

[yesthatsteve]

The one in my LaCrosse has been pretty accurate in the month I've had it. 4 fill-ups, each time within 2%.