On a recent 500 miles trip, I noticed that our RX 400h was more fuel efficient at 75 mph (24 mpg) than at 65 or 70 mph (22 mpg). This wasn't a fluke, I could repeat the experiment consistently and my wife confirms she observed the same.

Have you guys noticed the same thing?

 

nope, i've noticed the opposite!

 

It is not even possible to get better mileage at a higher speed. It takes more energy to go 5-10 mph faster and there is limited energy/horsepower from the battery and electric motors. The gas engine clearly has to work harder at faster speeds which equates to poorer mileage. There is no free lunch.

My mileage goes down dramatically above 65 mph although I can still get 24 mpg at 70-75 mph. I can easily get above this at 55-65 mph with good technique.

 

Actually, it is. Not by a huge margin (you won't get better mileage at 100 than at 55!) but by driving 5 mph faster you may get your engine in a more efficient section of its powerband, so that the extra power is more than compensated by the increased efficiency.

 

I would wonder if there is something wrong with your vehicle. The problem you are having is that you are only getting 22mpg at 65 mph. That is really low. Mine gets 26-27mpg at 65 mph but then it goes down dramatically at faster speeds. Your reading of 24 mpg at 75 mph is probably similiar to mine.

About a week ago I towed my 1800 lb boat for a couple hundred miles on the freeway at about 65 mph and I still got about 20-21 mpg.

 

I get about 27+mpg doing 65mph and 25-26mpg at 75mph. cdeslandes, have you check your tire pressure lately ?

 

i still get around 21-22 mpg doing 75 with my 20" wheels and giant ramming guard up front along with 200 pounds of stereo equipment in the back.

 

wind might be a factor.. but for our hybrid.. i noticed anything under is 60mph is optimal..

but doesn't the gas engine stay on full full time at 75mph does the hybrid system even kick in at that speed? can't recall.

 

recently completed 1500 mile trip in new RX400h (700 miles on odometer when trip was started). Did lots of mountain driving and tried to go 67-70 MPH when permitted. Averaged 26.7 MPG for the entire trip. Quite a bit of weight in vehicle too.

 

I'm about to take mine's from FL to NJ round trip.. Hoping I can manage atleast an average 26MPG ...

 

70 MPH, A/C on, 26 MPG. My mom can manage 28 MPG somehow, without cruisve. I don't how she does it.

 

Our new 450h has just over 600 miles now. Hwy speed has been between 65 and 70 on cruise mostly and city speed has a lot of stop and go and hills. Average since last tank and overall average by the computer is just over 30. Very pleased.

I did meet someone at the grocery that had 60,000 on his 08 h and was getting 28 on trips and about 29 average. I don't know his driving patterns.