The last 3 times I have filled up with Premium 93 Octance gas the actual mileage and the computer read out have been off by at least 1 mpg.

323 Miles 18.25 gal 17.70mpg Computer 18.9

317 Miles 18.10 gal 17.51mpg Computer 18.7

333 Miles 18.85 gal 17.67mpg Computer 18.9

Does any know why the discrepancy between the 2?

I drive 50% highway and 50% stop and go. When I fill up I make sure that not another drop can enter the gas tank before I stop pumping.

Is anyone else having this happen to them? Is this something that needs to be checked out?

The vehicle is a 2008 RX350 with 11,500 miles.

Thanks for your feedback.

We have found that our computer readout v. the calculated method to be very close, within less than .25/gal. computed over 45k miles. Ours is an 05 RX 330.

My 04 RX consistently overcalculates between .7 & 1 mpg

Same experience with my '09 RX350 as well as with my previous '06 GS300. Computer consistently gives higher mpg.

That's perfectly normal. The computer is only an estimate of actual fuel mileage. It should never be relied upon for actual fuel consumption.

That is all I want anyways, otherwise if we were going for high MPG would buy a smaller car with a 4 cylinder gas savings engine.
WE BOUGHT A LEXUS. Premium fuel & not the best MPG but Oh what a ride.

We have a premium user!!!!!

Didn't use Premium on our '04 RX but with the gas prices down & with the '09 RX we have used it 100%.

Y'all got more than one! I use nothing but premium in our 05 RX (and in our GS too). I've taken enough trips, climbed enough mountian passes where the premium provides me with better acceleration, ability to pass, and better mileage. Of course this is a topic that has been beaten to death on this forum

yeah I know this subject has been beat like a red headed step child,but it`s still fun to bring up.

On what are you basing this statement? Just curious, because I would expect the computer to be MORE accurate that the pump at the local station. The engine computer certainly knows how much fuel has been injected into the cylinders, and other systems know how many miles you've driven since the last fillup.

Having said that, I don't understand why the computer always reads higher.

Nothing is accurate.

Automatic shut off from fill to fill can be off.

Miles read by the vehicle can be off [but that is common to both calculations]

Actual amount of fuel injected can be different from what the computer thinks was used [no real measurement is done ... a slight variation can add up over the revs]

Lastly, the computer when they work. produce the same result, which may not be accurate. We have accepted the inaccuracy of computers to calculate 2/3

I only use the mpg indicator to improve my driving habits.

Salim

ps: The volume of gas purchased is at least calibrated at the pump per state laws.
The odo has a resolution of 1/10 mile that also can introduce part of the discrepancy.

Read your owners manual on the subject and you'll see.

On a related note - how accurate is the "Cruising Range" readout in everyone's experience?
I am on my 3rd tank of gas and have approx 30 miles to empty according to the trip computer. My low fuel light has not yet come on.
Also, from experience, approx how many miles of "reserve" fuel does the RX have once the low fuel light comes on? 20? 40? completely realizing it depends on many factors....Thx