What is the yellow line telling me that moves as you drive...Something about mpg I know but makes no since to me...Seems useless...What am I missing...This is on the nav. screen Trip Info..Looked in book but still no savy.

 

It's telling you instantaneous MPG. The numbers below that are average since you a started the engine or b refilled you gas tank. In the non-NAV vehicles you get to see both as numbers as numbers (digits), although the instantaneous changes a lot, just like that yellow bar changing a lot.

Note the bar positon while waiting for a light to change; infinite gallons per mile as in zero MPG. Makes a case for turning off your engine at longer lights.

 

Banjo:
I agree that this feature is useless. My bar display (nav screen) is erratic even at a constant speed on a flat straight road. Seems like Lexus could have done some data averaging to make this feature more useful.

 

Yes, I am still scratching my head..I don't see what it does...I know I am not smarter than a 5th grader for sure..

 

I'm not sure how the "instantaneous" mpg is being driven on the RX. It could be a measure of engine vacuum which is a pretty good indicator of the load placed on the engine at any one time - thus proportional to actual mpg. A more sophisticated approach is to actually meter fuel being delivered to the engine (on FI setups a second meter is installed in the return line to the tank and that value is subtracted from the first meter to drive the display).

Because your ECU monitors both vacuum and fuel delivery, it would be a relatively simple matter to display either of these parameters, although I suspect Lexus is taking the reading from engine vacuum, due to the sensitivity of the display to throttle inputs. A computer function that integrates engine vacuum and wheel speed (from the ABS sensors) produces a relative number that is indicative of your actual mpg at that moment.

You can learn a great deal from this display, if you want to save gas. A steady throttle foot is your best asset. Driving on the cruise control is wasteful as you can see the system working to slavishly maintain a constant speed. On slight grades the system adds throttle to maintain your setpoint regardless of what it does to fuel consumption. If you switch off the cruise and maintain a constant throttle opening you may lose a mile or two per hour, but your fuel consumption drops precipitously. Don't worry about your loss of speed, you'll get it back after you crest the hill and start down - again without a change in throttle position.

As JasDmw says, the display will quickly indicate the value of shutting the engine down when stopped, but a hybrid RX400 would do that for you (unless the logic system dictates the need to keep it running - as in getting the engine up to operating temperature). One cause of that display jumping around on a hybrid is the operation of that control logic switching and adjusting power sources from the ICE to the motor(s).

Although it is instructive to watch, don't put too much faith in the actual display. On my 330, that "miles to empty" is so pessimistic that when it reaches zero, I have over 40 miles range remaining. Think of it as not so much "miles to empty" as "miles 'til you dip into your reserve".

 

This screen just seems to be a waste of space.

 

the display on the non nav is so rudimentary its embarrassing. I wish Lexus invested more into that feature. Maybe like put in Lexus Personalized Settings in it so people could change themselves? Tire Pressure? vehicle Diagram? Current Speed? Oil Level? Date? And maybe if it had a Memory feature!!! As soon as you shut off the car its rests everything back to 0. Very annoying especially for the timer; sometimes i forget to check till its off.

Its so large; almost as if Lexus had to much room left over and needed to fill it with something. Then again old people drive the RX maybe thats why the Display is so LARGE. a coin holder or a storage bin would have been great. like on our old ML320. right below the radio.

ps. ML sucks don't even think for one second I'm praising it in anyway

 

Sorry for bumping this old thread, but can anyone tell me if there is a trick to getting a trip duration/timer to show up on the Trip Info screen? That is about the most important piece of information about my trip and it is nowhere to be found. (this is on an '09 RX with Nav)