Genesis average mpg indicator very optimistic.

[Disaster]

Has anyone else noticed the average mpg is very optimistic. Ours averages about 22mpg but the gauge reports about 1-1.5mpg better than that. Just took a trip. The gauge reported 27.1mpg (early in the trip it reported 29mpg but that steadily got worse despite the driving being the same...almost all highway.) Refilled it and the actual mileage was 25.3mpg (223.8miles/8.839gallons.) Considering the vehicle speed reads about 4% high, the actual mpg should be likewise 4% lower than that (since the distance traveled is actually less), or 24.3mpg highway. The reported mpg, is a full 10% higher than the actual mpg.

 

[dtreter]

I've been very pleased with the mpg for our Genesis 3.8 sedan. On 300 mile trips from Pittsburgh to Philadelphia and at speed of 75 mpg, we get 28-29 mpg. On the return trips, we get 27-28 mpg. The difference is due to the differences in elevations. These figures were on expressway (turnpike) driving and through the mountains of PA.

Local driving, we get 18-19 mpg. All told, slightly better than the 18-27 estimates that were on the sticker.

 

[dataguy]

This has been pointed out several times in the past. The trip computer not only overstates MPG but keys off of recent driving behavior. Thus, the overstatement can be high if you go from one extreme to another (e.g. highway to city). I've had cases where it showed over a full tank an average of 21+ MPG and it ended up as 18.5 actual.

And while computing average MPG should be done by mileage divided by fuel pumped, technically, you should use the same pump, same station, same time of day, and to the same cutoff point for both fillups for complete accuracy.

In short, it's an estimate, and that's why the DTE display flashes '--' at 30 miles.

 

[dond13]

Has anyone else noticed the average mpg is very optimistic. Ours averages about 22mpg but the gauge reports about 1-1.5mpg better than that. Just took a trip. The gauge reported 27.1mpg (early in the trip it reported 29mpg but that steadily got worse despite the driving being the same...almost all highway.) Refilled it and the actual mileage was 25.3mpg (223.8miles/8.839gallons.) Considering the vehicle speed reads about 4% high, the actual mpg should be likewise 4% lower than that (since the distance traveled is actually less), or 24.3mpg highway. The reported mpg, is a full 10% higher than the actual mpg.

I agree, but it has been the same on every car I have owned that had a MPG display. I have kept track of every tank of gas that I have used through 7000 miles and the best I got on one tank was 25.9. The indicator on the car showed 27.5 for the tank and that is about average for the difference between Quattro Pro calculation and the car computer. What would really be nice is a 'flow meter' that could give a very accurate measurement, but I don't believe any car has that.

Most of my driving is in a semi urban area, but I drive on controlled access quite a bit and the average MPG for 7000 miles is 21.31, which I still think is pretty good for my type of driving and for the size and weight of the car.

 

[Disaster]

And while computing average MPG should be done by mileage divided by fuel pumped, technically, you should use the same pump, same station, same time of day, and to the same cutoff point for both fillups for complete accuracy.

The pump doesn't make a lot of difference, when you consider the difference, from pump to pump might be a couple cups of gas at most....maybe a tenth of a gallon. On a fill up that accounts to about a half percent error.

I agree, but it has been the same on every car I have owned that had a MPG display. I have kept track of every tank of gas that I have used through 7000 miles and the best I got on one tank was 25.9. The indicator on the car showed 27.5 for the tank and that is about average for the difference between Quattro Pro calculation and the car computer. What would really be nice is a 'flow meter' that could give a very accurate measurement, but I don't believe any car has that.

Most of my driving is in a semi urban area, but I drive on controlled access quite a bit and the average MPG for 7000 miles is 21.31, which I still think is pretty good for my type of driving and for the size and weight of the car.

Our Volvo was pretty accurate...within a percent or two...for both speed and mpg. It would read 21.8mpg and we'd get 21.5mpg...or 22.1mpg. It seemed to error both ways.

I wonder if more people think they are getting higher mpg because they go by the gauge, instead of the actual mpg. Your 25.9mpg is just a bit better than ours...but ours were on snow tires which are probably less efficient.

 

[wallymn]

Has anyone else noticed the average mpg is very optimistic. Ours averages about 22mpg but the gauge reports about 1-1.5mpg better than that. Just took a trip. The gauge reported 27.1mpg (early in the trip it reported 29mpg but that steadily got worse despite the driving being the same...almost all highway.) Refilled it and the actual mileage was 25.3mpg (223.8miles/8.839gallons.) Considering the vehicle speed reads about 4% high, the actual mpg should be likewise 4% lower than that (since the distance traveled is actually less), or 24.3mpg highway. The reported mpg, is a full 10% higher than the actual mpg.

Covered in another thread but; the speedo error is by design, The odometer is spot on, so the miles covered (used to compute MPG) is accurate not off like indicated speed.

As for the computer guestimate on MPG, I found mine is off .6 to 1.0 MPG

 

[JamesD]

You would think that with the fuel metering as precise as it is (on virtually every car, these days), the calculated fuel economy would be very, very close to actual. Consider that the engine computer fires the fuel injectors, and sets pulse duration, timing, everything, to maintain emissions...it knows EXACTLY how much fuel it's injected into the engine. Also, a car with nav could use the gps info to track the actual distrance travelled; the car magazines' test gear is now mostly gps-based.

I think the lack of accuracy is simply due to the fact that it isn't really important that the readings be perfect, that they are "close enough" for the intended use. The manufacturers use simple techniques for determining fuel use and distance...in fact, I remember reading that some Fords used a technique for estimating fuel use that didn't involve actually measuring it even indirectly...wish I could remember exactly what it was, but I remember being dumbfounded when I read it.