i own a 2007 RX 350 and the best i ever got was 17mpg (50% city 50% highway)
i use 95 octane fuel and my car has run 6250 miles.
i bought it new and followed the lexus recommended run in procedure, kept the revs low and didnt go too fast.

thought the mpg was low cause its usually driven fast, but have been staying below 70mph all the time and its still low!!
all the routine service has been done at the dealer and they too dont have an explanation as to why its low.

any ideas? im in the middle east and its hot here, but will that cause this big a difference when most RX350 owners get 22-23mpg??

 

17 MPG with 50-50 highway and city is low. Not surprising, but low. If it were all city...still you should hit 20's. Too rich maybe?

 

Middle East - heat, and fuel quality could very well be the causes of low mileage.

 

I don't recall the Emirates as having much in the way of hills, but I found that a few small things can add up to a pretty drastic effect on fuel consumption.

First, if you can drive with a rather constant throttle opening (holding a steady foot and disengaging the cruise control) you can make a considerable difference - on the order of 3-4 mpg. The Lexus cruise control is very rigid about maintaining your speed at the setpoint no matter what. This can lead to heavy acceleration on hills just to maintain speed, rather than letting a couple mph bleed off when going uphill.

The chemistry of your fuel seems to make a difference in my experience as well. The E-10 blended fuels (10% ethanol) deliver a bit over 2 mpg fewer miles than straight pump gas. There simply isn't the energy available in ethanol that there is in gasoline and it simply takes more of it to deliver near-equal performance.

Finally, the grade of fuel seems to have a bit of effect on mileage. I find that the extra 20 cents per gallon I pay for premium approximates the improvement in mileage over regular, making the cost per mile a wash. Quicker throttle response is a bonus.

If after 6K miles your RX is delivering poor mileage, try pulling the FI fuse or simply remove the negative battery connection for about ten minutes. This will cause the engine computer to reset and begin re-learning your driving habits. Give it a few hundred miles and check your fuel consumption again.

When all else fails, consult your dealer

 

i only get around 14-15mpg on 87 octane

 

You may try different fuel, gasoline formulation change over time and region.
Also try 0w-30 synthetic oil such as German Castrol, protects the engine at hot temperature but better flow before reaching operating temperature.

 

i have never used the cruise control, always a steady foot.
there are absolutely no hills here, its completely flat.
i use 95 octane fuel, i do know there is a high sulphur content in the fuel here and thats why we dont get the GS350 here as they cant run on the fuel here.

 

Maybe the air conditioner? Try switching to Auto and set it to 77-78 and see if that helps.

 

it is always on auto with recirculate and temp at 75 F. if i increase it to 78 its gonna blow hot air!!!

 

also what tyre pressures are you guys running?

 

33 psi, front and rear.

 

if youre in the middle east, shouldnt be petrol be very cheap over there? (if its cheap why worry about mpg?)

 

I was going to ask the same thing. He's just worried the car is not performing as it should be?

 

Why use 95 octane?

 

well just concerned if there is something wrong with the car, otherwise i dont care if its 10mpg or 20mpg fuel is cheap.

@gman, most gas stations have 95 as the lowest grade!!!! though i have seen a few with 91 also, nothing lower.