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Instantaneous/Current Fuel Mileage Indicator

Old 01-06-2019, 10:09 PM
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Join Date: Feb 2011
Posts: 7
Default Instantaneous/Current Fuel Mileage Indicator


Anybody ever wonder what the real fuel mileage is when you are driving your hybrid down the road and the gas engine is running???

The meter on the dash says that much of the time I'm getting 50 MPG. Silly me, I believed it - for a long time. But being the curious type, I grabbed a free Android OBDII code reader app and my bluetooth OBDII dongle and spent the last couple of days monitoring what the car is doing and it was a bit of an eye opener.

Folks, Hyundai is lying to the tune of greater than 100% over statement of the actual fuel mileage when the gas engine is running. I'm a little peeved.

I have no complaints about the end result, which is, the average fuel mileage reported varies between 42 and 52 MPG. I have 3.5 years of records where I've verified the fuel mileage of every tank of gas and what I've found is the reported average fuel mileage is approximately 6 - 8% higher than what I calculate. Of course I'm assuming that the odometer and fuel station pumps are "accurate". At fill up today my reported tank average was 46.1 MPG. All in all, not too shabby.

But back to the instantaneous/current fuel mileage. I'm really unhappy to see 22 - 25 MPG reported by the engine ECU showing on my phone while at the same time, the dash display is merrily telling me my car is so incredibly efficient by pegging the meter at 50 MPG.

I always wondered why I would be driving along with the instantaneous/current fuel mileage indicating 50 MPG and see the reported average fuel mileage drop down a tenth of a MPG - while going downhill!!!. Now I know. Hyundai is "massaging" the data they display in favor of leading owners to believe they are getting better fuel economy than they really are.

I understand that the number is lower because the battery is also being recharged when the gas engine is propelling the car but I don't see any real reason to not report what's going on honestly/accurately.
Old 03-17-2019, 02:56 PM
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Join Date: Sep 2016
Posts: 13

I did once read about the measures used by these Android/OBD2 apps, they use some of the sensors of the car, but most likely not all of them and not in the correct equation. I would rather trust the car's computer vs an OBD2 app

As for the average mpg, we had the exact opposite problem with our 2015 Sonata 2.4 Limited. The average fuel consumption on the car computer is pretty high, around 15 mpg (yes, that high, with mostly city driving) but we recently compared this just the same way you did - with the gas bills and miles done for about 2 years (these gas bills are used for income tax refund as the car is also used for business trips). To our surprise, the actual average mpg for 2 years, from the gas bills, was rather 22 mpg! So basically the car's computer did show a much worse fuel consumption than the real one. Not sure what to think about this (besides being happy the car has reasonable real mpg for city driving), we had two sensor issues, VPM and a knock sensor, not sure if these would have confused the car's computer mpg calculations.
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