My 2009 RX 350 returns poor gas mileage in city - only about 15 if I drive cautiously - slow & smooth acceleration, max speed about 40-45 mph, average speed about 15-20 mph, Stop and Go traffic. Driven mostly single.

Can I know some of the other members results?

On the highway, its about 21-22 mpg which I think is poor too... Any suggestions to improve this number?

- Tire pressure suggestions for michelin tires?
- Should i reset the ECM?
- Speed suggestions? How to get to higher gears sooner?
- Change filters?

All suggestions appreciated. Thanks!

 

I think your results are poor as well. I have a 2004 RX330 which is not as fuel efficient as a 350 and I get 22-23 city and 26-27 highway. This is measures MPG not the NAV results. I use a fairly easygoing driving style with the Lexus. I typically burn premium ethanol-free fuel and generally do most of my driving in rural or highway/expressway settings. My average over the life of the vehicle (9 years) is 23 MPG.

I have Bridgestone Alenza tires inflated to 31-32 psi.

What does your service manager have to say about this?

 

You do not say if you have AWD or not. Assuming AWD is present, the fuel economy ratings for that vehicle are listed at 17/22. FWD rates out at 18/23. So, you are well within the margin of error set on the window sticker. Some will get better and some will get worse than the listed fuel economy ratings.

You can try running your tires at 34-35 psi. However, keep an eye on how they wear and note that you will give up some stopping distance in doing such.

For your oil changes, make sure you are getting 5W-20 or 0W-20.

What fuel are you using? The 2nd Generation RX350 should only be using premium fuel. The Owner's Manual states for you to use 91 octane or higher. Also, some vehicles do better with a different brand of fuel. Is a bit odd, but I have seen it happen over the years. Not worth going out of the way to fill up though.

http://drivers.lexus.com/t3Portal/do.../sec_01-05.pdf

Finally, how are you measuring your MPG? Fuel used over miles traveled or by the trip computer?

 

I think your biggest problem is you are never hitting fifth gear, mine won't shift to fifth until at least 45 mph.

If you have not changed air filter, that might help a little. At 15-20 mph average, no non-hybrid vehicle is going to do well.

 

Was it always this low or has something changed? If it was always this low since new, then I'm at a loss. If it has slowly gotten worse, then look at cleaning your MAF sensor, clean your throttle body, change your air filter and reset your ECU.

 

Thank you ALL for first your time, and excellent suggestions. I am going to try most of them. I used the "Regular" Fuel in CT.

What happened is, the first time I used regular fuel without knowing (i bought it used at 50K miles). It returned a good MPG as I drove back on highway averaging about 23.5 MPG. By the next time I read the manual and used "Premium" (the expensive one) fuel and noted the highway mileage at 21.5 . The third time, 'regular' gas again and the mileage got back to just about 23. After that I never used for highway driving, and started replacing my civic - used for office commute which is fully city stop and go kind of traffic. MPG plummeted drastically to about 15 and hence the mail.

Would any of your suggestions change based on the above facts?

Ram

 

My millage has dropped during city driving as well. I use only Premium fuel, and I think it`s this friggin crappy Ethanol laced fuel we have shoved down our throats now.

 

I have an 04 330 AWD. I know i have a fairly light foot but I get anywhere from 17-19 city and 23-25 highway. Forgive me for this but I use 10% Ethanol 87 grade gasoline. I use 10% Ethanol 91 grade (highest I can get in my area) every 4th or 5th tank but it doesn't seem to effect fuel economy any. However, if i mash the gas all the time in the city and go 80 plus on the highway (only in a 75 of course) the mileage nosedives to about 16 city and 20 highway.

 

The RX330 is a bit more forgiving when it comes to using regular gas in the tank compared to the 2nd Generation RX350. The 2nd Generation RX350 should really only be using 91 octane or better while in the RX330 it is recommended to use.

FWIW, the new 3rd Generation RX350 states you can use regular unleaded in the Owner's Manual, however, the engine has been retuned over the previous generation.

 

AWD: 18-20 City 22-24 highway

 

You haven't mentioned how you calculate your fuel mileage? Do not go by the onboard display in the RX. It is not accurate on a per tank basis.

 

Thanks... my calculation is based on full tank gas to the next full tank, and the miles run in between....

Based on one of the above suggestions - today I reset the ECU myself, after doing some research online ofcourse, by pulling out 2 fuses from the fuse box... i will post back the results after testing...

 

OK all - here is the update after a few weeks of driving.

I did the ECU reset on 13th of this month. After that, i noticed the small change in city driving which resulted in 16 MPG. I am very light on the gas pedal, and try to coast as much as possible. My office is about 6 miles, and hardly the vehicle warms up.

However, the highway mpg has IMPROVED tremendously from 21-22 mpg to 27 - 28 MPG solid. I took for two stretches 65 miles each, and consistently doing about 60-65MPH. The result MPG was great.

ECU reset does work. Also, i am now going to change the tire pressure as the next step. Any recommendations how much can it be bumped for a safe ride, also a smooth ride.

 

I run 30-32 psi. Any more and I feel too bumpy.

 

I avg 19.5 combined, running at 32 psi. For AWD, I think that's right in the average.