My 400h is almost at 140K and I used regular since I got it. Averaging 27MPG driving in Chicago and burbs

 

Our 2006 RX400h AWD (135,000 miles) seems to get the same mileage ~26.4, on 87-93 octane. However, when using 91 Octane with no ethanol , it goes up to 27+ which is understandable since ETOH has less BTUs per volume. This is all with gentle driving. I expect the highest performance (acceleration) would come from 93 octane with 10% ETOH.

 

Thanks to all for the helpful postings. Looking to purchase '08 RX400h from Elite Dealer this week. Will be checking back frequently for continuing guidance, news, and commentary.

 

I always used 91 octane but started using 89 a few days ago. Did not notice ANY difference in performance or mpg (26).

 

I'm using Premium 95 in the land of Oz.

 

You guys are going to shorten the life of your engine by not using the correct gas.

The gas grades combust differently.

28MPG is what you should be getting on the rx400h even without driving efficiently.

 

Go here:

 

Still using 89 octane and getting 27mpg combined (30+ freeway)
I'm actually more worried about the hybrid battery giving up than the engine.

 

Watch this one. Reckon RX400h batteries would be same.

 

Not if you drive the way I do and under the same conditions.

 

We've had our 2006 RX400h for about a month now, and didn't think much about fuel octane until recently. The manual says, "Select Octane Rating 87 or higher. For improved vehicle performance, the use of premium unleaded gasoline with an Octane Rating of 91 or higher is recommended." From that I figured 87 (10% ethanol blend) was ok, and was getting between 22-23 mpg mixed driving, but mostly around town, and babying it. I thought I'd try premium, and put 93 in it the last two times I tanked up; it's now averaging 25.6, even with some more "spirited" driving. I was always pretty skeptical whether octane made much difference, and have rarely seen much difference in other cars that I've owned, but apparently these things like the good stuff. I need to run some numbers to see if it's worth the extra 30-50 cents a gallon to get an extra 3 mpg.

 

Don't conflate higher octane with good. A vehicle will only benefit if designed to run on higher octane.

 

That's not a very credible source of info on gas.

The gas cap says in large letters: PREMIUM FUEL ONLY.

 

Believe what ever you want. I use 87 in mine and get 24-30 mpg and no knocking.

 

Hmmm... My clone HiHy has same 3.5L engine, right? And runs on 87 doing 30.8 mpg as I type? All it says is Unleaded Fuel Only.
Maybe they simply use door from RX350?