OK....I filled up my tank and reset the trip computer including the mpg calculation. A week later, I refill the tank with 12.28 gallons. I had driven 227.9 miles. The car said that was 20 mpg. BUT....227.9 divided by 12.28 equals 18.56 mpg.

Any ideas???

 

20-18.56 = 1.44

With rounding in play, I would say round 18.56 to 19, and you are off by 1mpg.

I think that it's accurate enough, but does it really matter if you actually took the time and did the math and figured out it was 18.56mpg in reality? You could just say okay take car MID mpg and subtract by one and call it good.

Just a thought.

 

Valid point. I guess with all of the features on these cars (tire pressure to the exact PSI, etc), I was thinking it would be dead accurate. Not a big deal, but it did surprise me.

 

I have found the MID very accurate. There are lots of variables with the biggest being the gas pump and when it clicks off. I go to the same gas station most times and I'm within .5MPG of actual most of the time. The mid will usually be just a tad high because of the rounding.

 

Well, I have refilled only 5-6 times till now, but travel abt 330-350 miles with 12.3-12.5 gal every time . I am surprised by that. Getting off BMW with 16-18 mpg mixed driving (highway mostly) to 27-28 mpg (same driving habits) . Also the math is correct by what the board comp reads and the hand calcs shows.

 

Did you fill up at the same station both times? One station's pump stopping at "full" might be less full than another station. Just a thought.

 

MPG various tremendously by gas throttle. I guarantee that if you use cruise control more often you will get a better MPG. MPG for any car is based upon grandma driving the car and taking off very slow and barley using the gas. Also over 55 MPH, you actually start to kill your MPG.

 

Everyone's experience is different.
I agree 100% about a soft foot on throttle being absolutely necessary to get the best milage...not too sure about your comment about 55 mph
I almost always get over 32 miles per gallon on road trips travelling at 72-83 miles an hour with a 3.2 TL.
The key is, if you encounter any uphill slopes, take it off cruise control as cruise will hammer the throttle in an attempt to get back to the set speed as fast as possible.

Just came back from a trip to and from Flagstaff Arizona(486 miles each way) and the fuel "low" light never even came on..used about 14.5 gallons each way.
By the way the Arizona speed limit is 75 mph, so you know I was exceeding that but at least 7-10 mph.

I actually think my car gets worse mileage at 60-70 mph than 70-85 mph.!!lol

 

MPG is determined by average mph more than any other factor. This has been gone over time and time again. Average mph is more important than driving style.

Cruise control can match a good driver on flat ground but it will kill mpg on hilly terrain.