Originally Posted by cmmetcalf

Consumer utility is always computed in micro-economic theory as relation between the amount of goods consumed as to the amount of happiness or satisfaction the consumer gets from that consumption. The micro-economic theory says that "economic man" will always base their individual decisions of the basket of good and services purchased based on maximizing total utility.. Thus, in the mathematical sense, that point is reached when the sum of all the marginal utilities is greatest. As long as the consumption produces a positive marginal utility (the utility gained by buying one more unit of a good (marginal benefit) vs. the additional cost of acquiring that good, i.e., Marginal cost) the consumer will buy the good.

Since I teach it, I can state that this concept used in many micro-economic models and the concept that "economic man" always acts rationally is being challenged by the thought that human beings don't always act rationally and the reduction of economic behavior to the earlier models of consumer behavior is not strong enough to provide a full explanation of economic activity and markets.

In my discussion I was very careful about stating that it was a marginal cost vs. marginal benefit analysis,. That is simply: the marginal benefit to buy and use premium against the marginal benefit of gaining fuel mileage by that choice was not favorable toward the use of premium when the marginal cost of 87 produced better cost/benefit results.Or stated another way: "Why would you pay 25% more for a fuel that only generated a 5-6% increase in fuel economy.when regular (87 AKI) was what the manufacturer recommended for the auto and the automobile performs acceptably with that fuel grade in the tank?

To be sure I noted that the consumer satisfaction or "happiness" could certainly cause one to decide on premium vs. 87. If it makes you "happier" (greater marginal utility for premium than 87) to buy and use premium, then by all means do so---it isn't the best marginal benefit/cost scenario, but the expenditure is entirely up to the amount of "happiness" you get out of the transaction. Lexus strongly recommends Top Tier (registered trade mark) gasoline (2020 Lexus RX350 Owners Manual page 459) not premium. This certification indicates that the additive mix blended into the brand's gasoline meets the Top Tier specification for such gasoline grades. Virtually every major producer and reseller of gasoline in the US, Canada and Latin America (and Costco is included) is a Top Tier refiner/retailer. See TOP TIER™ Gasoline Brands (toptiergas.com).Licensed Brands.In July of 2016, AAA published a study conducted a study on quality gasoline vs other grades that showed the Top Tier brands were 19 times cleaner than non-Top Tiers brands.

AAA: Not All Gasoline Created Equal | AAA Newsroom

Of equal interest to me was the survey finding on consumers:

· Three quarters of U.S. drivers choose a gas station based on location (75%) or price (73%).

· Nearly 1/3 (29%) chose a gas station based on a rewards program.

· Only 12 percent of U.S. drivers choose a gas station based on whether the gasoline contains an enhanced detergent package.

· Nearly half (47%) do not regularly buy gasoline that contains an enhanced detergent additive.

· Men (44%) are more likely than women (26%) to buy a gasoline that contains an enhanced detergent package, as are baby boomers (41%) compared to millennials (32%).

The article stated: ““Americans are six times more likely to choose a gas station based on the price of gasoline rather than the quality of the fuel,” continued Nielsen. “Since TOP TIER gasoline is widely available and only an average of three cents more per gallon, AAA urges drivers to reconsider their priorities when selecting a gas station.”

In short from the perspective of what gasoline grade to use, it would appear that both Lexus manual recommendations and AAA's research results lean towards a conclusion that enhanced additive formulation is a better bet than "premium" as the engine runs much cleaner thereby reducing intake carbonizing as well as most drive-ability issues. No where in their manual for my car or in their on-line gasoline specifications do they recommend greater than 87 octane for the RXs until you get to model year 2011. For 2011 through 2006 they recommend premium and then go back to 87 for the RX330s and RX300s through 1999. Which fuel grade should I use for my Lexus vehicle? (custhelp.com)

This discussion is not intended to add fuel to the 87 vs premium issue. It is a simple presentation of facts that might be considered when choosing which fuel to burn in the wonderful RXs that we all own and operate.
It would likely serve no further advancement for this discussion and I certainly agree with one commentator that it could be closed until some new facts based on research come to light or Lexus changes its recommendations.

My father was general manager of several major oil company's refineries in his career and I spent one whole summer doing RON and MON tests using the rating engines for the ASTM standards (as well as spending 5 years in major oil marketing, distribution and product supply myself. This is a subject matter with which my family and I had some extensive experience--- so Top Tier 87 for my RX. You do what makes you happiest.

With respect for all and be safe....

Originally Posted by cmmetcalf

..... when regular (87 AKI) was what the manufacturer recommended for the auto ....

Originally Posted by dibl

This horse seems pretty dead, but I feel forced to give it one more lash with my flog.



No, the manufacturer did NOT do that. The manufacturer was quite careful NOT to do that. At least not in my 2015 or 2018 owner's manuals. No one has yet posted a manual page that says that. The manufacturer WOULD HAVE written that, if they intended to say that, but they did NOT. For good reason, I'm sure.

OK, now I feel better -- LOL.

Originally Posted by DocRock

Here's the recommendation from the 2020 Lexus RX 350 owner's manual:

Originally Posted by DocRock

Here's the recommendation from the 2020 Lexus RX 350 owner's manual:

Originally Posted by dibl

Yep. Same as my 2018. Note the conspicuous lack of the word "recommended". They published the performance specifications for the 2GR FKS engine, and they know what fuel they used to get those results, but they keep that information proprietary. They have to write a manual to inform the owners what fuel to use. They would prefer not to get sued for fraud by recommending a fuel octane rating that actually won't produce the performance results that they advertised, so they had the lawyers write the instruction "87 or higher". Good one, huh? LOL!

IMO -- I wasn't in the room.

Originally Posted by docrock

thank you, carnac!

Originally Posted by mrolds69

You want to see the word "recommended"? Here you go...Google Tucson AZ 2021 Lexus fuel requirements I have to check...I thought I locked this thread!

Originally Posted by Nail34

I tried regular gas twice and they were the only 2 times I got less than 20 mpg.
The price of regular gas is $4.90 and premium is $5.30 per gallon an 8% increase. My mpg on regular was 19.2 vs my well established average on premium of 21 mpg, a 9% increase. The 21 mpg is conservative and a mix of town and freeway driving, I have got as high 28+ on all freeway driving.
I filled up with premium today.
'17 F-Sport, 36,000 mile
The $.40 difference in the price of fuel has been the same for years and certainly was more significant when premium was $3/gallon. The price difference of reg vs premium is much higher in other states.

Originally Posted by bamalam

Interesting. I did a long term, 6,000+ mile test earlier this year and only found a .5 MPG difference between 87 and 93 octane. Full write-up is here: 4RX Mileage Thread - Page 23 - ClubLexus - Lexus Forum Discussion.