I've got a veey well maintained RX400H, and have a couple different apps for diagnostics, including the Dr. Prius app.
everything checks out good, including the hybrid battery.
I drive 40-50 miles per day, mostly back roads, with a few stop signs and roundabouts. 40-50mph average.
I'm only averaging 23mpg.
I was hoping to be around 30mpg.
I have checked the tires (32psi) ran injector cleaner thru a tank of gas, and cleaned the MAF sensor.
My car seems to only run on the electric motor for a half second before the ICE kicks on, even with a full charge.
I see the motor assisting the ICE often, but rarely does it seem to run on EV for any length of time.
I feel like it should stay in EV mode from a stop until 10-15mph, at least...
I have nothing to compare this to, other than a friend who has a much newer hybrid Rav4, and they get 30-40mpg...

 

if it's the original hybrid battery then it means that it has diminished capacity. My 2006 averages at 23-24 with mix city.hway driving.
see how others fare.. https://www.fuelly.com/car/lexus/rx400h

 

It's a 20 year old car, with likely a 20 year old hybrid battery. Not only were hybrids of this era not as efficient as those of the last 10 years, the batteries degrade over time.

My girlfriend has a 2006 hybrid Highlander and she's getting 22.5 mpg average (mostly highway), which seems not that far off from what most folks get in these older hybrids now.

You can replace the hybrid battery in the 2006-2009 models relatively easily DIY, and a new battery will run you about $2k-$4k depending on vendor. Do the math and see if that's worth it for you for how much you drive, it should get you up to the high 20s mpg.

 

Well, it looks like I'm right along with the average mpg of everyone else.
I'm going to do a couple more tune-up related things, and I guess I'll call it good.
I've switched to this as my daily from a 2002 F150 that gets 16-18mpg, so can't complain too much.

 

Only two recommendation on top of everything you are doing is…
1. ISC reset
2. EV / LRR tires.

Should give you that extra 1-2 mpg u r looking for.

 

sounds about right - the 2g RX is not widely known for 30mpg.

23-24mpg is the real-world average in the last 2 decades this car has been on the roads.

 

Now that winter is mostly over, and I'm not running the heater, so, therefore, the engine isn't running as much, I'm up to 24-25mg, and even got close to 27mpg before hitting the interstate, and deciding to see how the ol girl handled at well over 100mph... I thought I saw that these were electronically limited to 113, but I can testify that is not the case.
Even with worn front struts, it rode smooth and quiet at those speeds. You wouldn't know, unless you looked at the speedo.
Average is sitting at 25.5mpg now.

 

I run 40 psi on mine, ride is a bit harsher but mpg much better(it can get up to 30mpg on highway)
What matters the most for getting more mpg for me is acceleration. If I always start fast, motor immediately kicks in and I don't get any ev range. However when I start very very slow and try to keep it in ev mode for as much as I can, mpg is a lot better. Of course it depends on a lot of things and mainly hybrid battery health. But putting higher tire pressure will give you a few mpgs for sure.

 

oh god. I can’t imagine the rough ride at 40psi in the city. I do 33psi but always ponder going down to factory 30…

 

My work commute is mostly highway so I put more psi, but even with high pressure still a lot of factors that impact mpg. When I start my car is the morning before work I immediately turn on heat and seat warmer and mpg drops like crazy, I can only get it back up after work with everything turned off. Had to put higher pressure because those gas prices are crazy right now

 

And regarding the ride, it's not that harsh if you avoid EVERY pothole in the city😄, if all suspension parts are in good condition you shouldn't be hearing any noises when hitting a pothole

 

yea. I believe you. With the current gas prices, I wouldn’t be surprised even at 45psi. It’s over $6/gallon here.
I don’t drive the 400h much these days. Maybe 2000 miles total in the last 4-5 years. Just drive EV these days.

i still marvel at the hybrid tech when I drive the 400h though. It’s a great car.

 

How do you do and what is ISC reset?