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The ES350 has been tuned for 87 octane. Hence the engine may not make more than the official 268 hp even with premium 91/93 octane. Toyota could have tuned this for more hp but probably chose not to. I had an Altima with 270 hp and this car feels quicker, so it does make more, but being a conservative company, they think reliability and lower fuel cost is what sells. Just because you’re wealthy doesn’t mean you’re not stingy.

However, I believe the tier 1 gas suppliers have jacked up their premium fuel costs over regular grade so much in the last 10-15 years that they can definitely afford the premium additives, detergents and technology over regular. Plus the fuel quality issues that affected premium German cars since direct injection became prevalent led these gas suppliers to up their game. Hence using premium definitely runs cleaner, and smoother, than regular. I compared the soot levels in the exhaust and premium definitely ran cleaner.

Premium gas has the same amount or less ethanol than regular at the same pump. Premium gas is a different process at the refinery than regular. Higher octane lower energy density ethanol is not used to to increase octane rating in premium gas. Increasing octane rating does not increase its energy density, so gas mileage should not change.

Other Myths:
1. Premium gas will burn less efficiently than regular or have less complete combustion is false. Oxygen and catalytic converters don’t allow this to happen, the computer adjusts to avoid this. Premium burns just as completely, unless the engine has misfires or other problems, usually indicated by the check engine light.
2. Throwing in a fuel cleaner once in a while will have the same effect as using premium. Not in my book, prevention is better than a cure. Ask a heart patient!

Tier 1 gas suppliers have the best technologies to keep your engine clean, and more of the good stuff in their premium fuel. If you do a lot of low speed stop and go city driving, I would use premium almost all the time. On extended highway runs, I would use premium every second or third tank at least.

At higher altitude, conditions for knock in non turbo or supercharged engines is less. Hence the gas suppliers can sell gas of 2 points less and get away with it. A car running 87 octane can get by with 85 octane above 5000 ft elevation. However, as altitude goes up, the horsepower engines make goes down. At 12000 ft, a normally aspirated engine makes about a 1/3rd less power. Turbo or supercharged engines as less affected, and gas octane rating is not the culprit for loss of power, it is the lack of oxygen in the air as you go up in altitude.

These are my personal opinions based on my observations and experience.

The amount of ethanol that can be put into gasoline is limited by law and is stated on the pump. So you can’t add ethonol and then somehow neutralize it with expensive additives and call it premium.

You are correct. However they send a regular grade and a high octane grade to terminals. They add brand additives and ethanol at the terminals and then truck the gasoline to your corner gas station. The corner gas station has tanks only for regular and premium grades. The gas pump blends the regular and premium to make the mid grade gasoline.

it is interesting that gas is completely commodotized at the terminal. A terminal opened by ExxonMobil can make Shell and Connoco and other brands of gas simply by squirting their additives into the truck when it loads up. The additives and ethanol mix in the truck as it drives to the corner gas station. The truck driver has a credit card type of a card that (s)he swipes through a card reader and enters the amount of fuel to be purchased and the terminal provides the necessary additives to make Shell gasoline.

It is questionable what additional value the additives provide to the customer other than make them feel good.

It is 10% or less ethanol in gasoline. The ethanol industry is trying to push this up to 15% but this may cause problems with off road engines such as those in lawn mowers etc and older cars.

You can buy 85% ethanol E85 gas but you car needs to be rated for that.

Only other thing I may try is ethanol free gasoline. The heat of combustion of ethanol is lower than that of gasoline so ethanol free gasoline may provide a bit of extra power in the mountains.

I use King Soopers and Costco 87 gas too. There is an ethanol free station on Alameda and I may try that when the tank gets empty.

I find in’s that most of the time the ESh is OK but merging onto I70 going west from Denver West is hard on the car because it struggles to get up to speed uphill.

What experience have you had?

With the ESH, the electric motors don’t lose any power due to altitude. However, they only contribute between 0 and some speed like 30-40 mph. The gas engine part of the total power equation reaches peak power at higher rpms, say 5 to 6000 rpm or above 50 mph depending on gear or cvt position in this case. The gas engine is a Atkinson cycle type as opposed to the normal Otto cycle engine, which is meant to increase efficiency and gas mileage, rather than total power. Considering you lose around 30% power due to altitude, your 200 hp becomes 130 hp at 50 plus mph where the batteries and electric motors do very little. That’s why these hybrids are best in city stop and go, and frequently give a little less gas mileage on the highway, just look at their epa ratings! That’s why the ESHs and other hybrids are “dogs” at high altitude, nothing to do with 85 vs 87 or octane, period.