Originally Posted by Tekrep
I have a spreadsheet containing every fill up I have ever done, with calculated MPG. The lie-o-meter is usually 1-2.5 MPG off, consistently. After disconnecting the battery, it got worse. My driving is not consistent, but then I'm not sure if that matters. I only use it as a rough gauge. Last time I filled up, it said 18.0 and I calculated just over 16. Granted- I have slightly larger tires, so the error is closer to 1 MPG than 2 on that tank of gas.
I have also found that the the lie-o-meter is optimistic (by 1~2 mpg). I top off every tank, and reset the computer every tank. On my spreadsheet, I added a column that shows what the computer showed as my mpg vs. my actual hand-calculated mpg. Seems relatively consistent in terms of how much it is off from tank to tank. My truck is stock.