I know I've seen somewhere on the forums about the accuracy of the onboard MPG calculators in cars, but can't locate it right now.
Seems that they have an error of +/- 7% as I remember...is that right?
My '07 Camry has an electronic MPG calculator, and I will be starting a gas log to compare to it. Just wondering if anyone here has had any real world experience as to how close these onboard displays are?
It's definitely worth keeping a gas log, regardless of an onboard MPG display. You get all the data, it gets put on a graph for you, you get to keep other notes (like maintenance), and it becomes easy to track and compare.
Tire size can play a large role in accuracy. Even if the gauge was accurate to start with, a slightly different tire from stock will reduce it's accuracy. In fact, I imagine new deep tread tires to very worn out tires would have an effect.
I like that my gauge can be adjusted manually. (MPGUINO) That's really the only way to get close.
agreed, depends on the car, the method they/you're using to read it, calculate it, and display it. check yours at the pump a few times to figure out the margin for error and how to correct for inaccuracy.
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1990 Toyota Cressida 7M-GE 3.0 I6/5-speed manual
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My guess is that most factory-installed MPG displays cannot be calibrated. My 99 4runner doesn't have one but I put in an Ultra-Gauge (which is similar to the Scangauge in that it gets info from the OBDII port and calculates MPG.) I had to calibrate it a couple of times (first for distance and then for MPG) but now it's dead on, less than 1/10 MPG different from my hand calculations.