I don't think it will HURT the power/mileage because the test that Lexus or whoever that monitors the MPG's for each car use premium unleaded to test the cars with. I believe it even states it on the Lexus site that if you want to achieve the posted MPG's that they used premium unleaded. My belief is that it could help your car since it will make the engine run smoother but a waste of money since your car doesn't require premium unleaded.

 

no.. see that's the misconception that people have..
there are pages and pages of this discussion on the net, so i don't want to start one here.. yes, if the manufacturer recommends premium, put in premium.. if they don't, there's NO POINT putting it in..

 

for the Hybrid. No harm will be done to the engine if a lesser grade was used but mileage is expected to drop which would be counter to one of the motives for buying a hybrid in the first place. If there is no economic benefit to Regular there will be a slight difference in power output of the gas engine with Premium gas. You decide and what price spread amount is currently in your market. I'm still recommending Premium but if we go through another huge increase in gas prices that could change...

Rock

 

no doubt i put in premium as we speak..
i still didn't get a chance to check the manual yet.. (yes i am lazy)

 

I've been using regular for last 4 months with average of 25MPG. I just put in premium last week and surprisingly got 27.3MPG and I felt the car more response in accel.
I am thinking to keep using premium for now.

 

Had been running regular in my RX400h, but every so often I noticed the engine would ping under acceleration, so it's back to premium. At least gas prices have dropped so premium is now cheaper than what I was paying for regular a few weeks ago.