Fuel: Owner's manual says Minimum 87 octane with 91 for improved performance
 

I have been using premium (91-93), but this morning thought to check the owner's manual. It calls for a minimum 87 octane which is "regular" and goes on to recommend 91 octane for "Improved Performance". This suggests that Toyota used a knock sensing ignition timing system that advances and retards ignition timing if it senses engine knock or pre-ignition if lower octane fuel is used. Generally vehicles with this technology will have slightly reduced power and potentially reduced fuel economy if knocking/pinging is detected when using lower octane fuels. Thinking I will try a partial tank of 87 and look for fuel economy changes,....however, wondering if anyone has already done this.

So,....I am wondering if anyone has experimented with regular vs mid and premium grade fuels, and if so, did you see a variance in fuel economy? Im not concerned with power/acceleration as the 400h has more than adequate power,....

I ran 2012 HiHy which is same power train, for 2.5 yrs on regular only, and aced real good mpg.

Honestly, if you are just putting around, normal driving style, 87 will be fine. I've been running it in mine with no real change in MPG. Granted its getting warmer out now, so that helps. If you are in a real hot climate, slightly higher octance will help for knock control and power.

My owners manual for my 2006 RX400H calls for regular 87. I have always used regular 87.
There was a switch over point, maybe 2007 when they changed the engine, but it then call for premium.

I think all engines have a knock sensor to prevent damage, regardless of using regular or premium.