ronmarks

The EPA suggested mileage is 32 highway and 24 city, combined 27 mpg. I noticed when I checked the gas mileage myself that the highway mileage I routinely got was 28-29 mpg, while the onboard computer routinely gave 31-32 mpg. I have recently noticed at the EPA website and at a few car websites that it is common knowledge that the 2007 IS 250 routinely gets 28-29 highway mpg, agreeing with what I have gotten.

I have also noticed that the 2008 Lexus IS 250 is EPA rated at 29 highway and 21 city, combined 24 mpg. From talking to a 2008 owner, I understand his on-board computer yields 28-29 mpg for highway driving. I understand from my dealer that the engine is the same in both the 2007 and 2008 IS.

My question is why does my 2007 Lexus IS 250 computer suggest I am getting 2-3 more mpg than I am really getting? According to my onboard computer, the overall average mpg after 30K miles of driving is 27.2, what EPA says it should be in 2007 but clearly about 3 mpg more than I have achieved and should expect to achieve.

I have spoken with both my dealer and Lexus about this, but they keep suggesting it is my gas or air cleaner or tire pressure or driving habits, but none of these would explain the differential between the actual mileage and computer reported tank averages. BTW, I take excellent care of my car, drive responsibly, and use premium gas, so none of these issues apply.

Note that I am not unhappy with mpg obtained, the attained numbers are still good for this car, but I would like to understand this issue and why the on-board computer gives mpg numbers that match the EPA estimate for 2007, but the car actually gets lower mpg.

Thanks in Advance

slee18

iTrader: (1)

it is also dependent on the type of gas you get in your state. Many states have different formulas which give different types of gas mileage.

My onboard computer is pretty spot on with the tank average every time i fill up. I have never gotten close to the EPA mileage on my 07. I overall average is 25.2. How are you computing your MPG???

eternal07

it could be your avg speed.
Avg speed that computer calculate, can affect avg fuel little bit.
Usually when avg speed is lower, you get lower mpg even though you get more mpg. When avg speed is high, you get more accurate mpg reading.
Mine is little bit different too.

mvlbr

If I go by the computer I average out 24.5-25.0 mpg with mainly city driving 70/30 .

J_Hao

iTrader: (1)

on my computer, i average out 29-30 with 70% highway

kickin8

iTrader: (1)

ymmv

Fizzboy7

As a general rule, trip computers are not the best way to caculate MPG's. They are never perfectly accurate. The best way to get your numbers is when you fill up the tank and do the divisional math.
As far as the MPG ratings changing from 2007 to 2008, that is due to new EPA ratings. Nothing changed with the motor, but more realistic regulations forced manufacturers to revise their numbers to better reflect real world driving. So the numbers dropped on all models in 2008.
I look at it this way... if you drive easy, without A/C on, and don't get stuck in a lot of traffic, go by the old numbers. If you drive aggressive, get stuck in traffic often, or use the A/C a lot, use the new numbers. I drive very easy and never use A/C and I am averaging 24 in almost ALL city driving.

speed_Demo

I agreed in doing your own math calculation...and the onboard calculation not reliable.

MPG average will vary since everyone drive in different environment & situation. But you can't compare your MPG average to someone else MPG average...useless. EPA & factory number just a sample to what they tested, that doesn't mean everyone will get the same result. Seriouly, you sound unhappy.

For me, if i drive 65MPH on the freeway, my mileage(37) is better than EPA number.

chummer

True it all depends on the drivers, every time I fill up I calculate the mileage and gallons I put in the tank. I average about 24/25mpg.

SwooshICE

i have a 09 n the computer calculation isn't accurate either

meefer

iTrader: (8)

Yes YMMV, quite a bit

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kimban

read ther top to the screen. it reads "approx"

i've driven with the screen reading '0' for almost 10 miles.. lol, yes i will never do that again!