Gasoline Grades

[Phil]

First, I assure you I would never use Regular in my '03 LS430. I purchased the car new in February and used nothing but Premium. However, on a long trip I used two full tanks of the medium grade, one after the other, and noticed no difference in performance, gas mileage (25-26 ib on the freeway) and no pinging. I understand the computer automatically adjusts for this, but will it hurt the engine anway? A mechanic once told me that if the car doesn't ping, "no harm, no foul". True?

Your input would be apreciated, Thank you, Phil, Grants Pass, Oregon

[petrojeff]

Okay let me try to be as concise as possible............ Gasolines are composed of hydrocarbon chains some long and some short. The primary chain (Octane ) in gasoline obviously has eight carbons. These carbons are attached by bonds, and the removal of these bonds by the addition of O2 (oxygen) causes combustion which results in heat and the production of CO2 and H20. In a perfect world. Alas the evolved Lexus engines of today, have high compression ratios in order to create more HP. In the old days, before engines with integrated electronic sensors, with feedback loops., timing was manually set and could not be changed. Therefore in high compression engines it was necessary to run fuel with higher octanes or higher octane equivalent numbers, or there would be the pinging caused by predetonation in the combustion resulting from the higher pressures breaking the bonds in the hydrocarbon chains of the regular fuels. The answer was to come up with higher octane fuels requiring more energy to break the bonds which meant the bonds would break at the higher pressures and not ping, also resulting in more HP since you were breaking more bonds. Today's mid range and premium fuels have higher equivalent octane numbers which are attained by the addition of proprietary ingredients from the major oil cos. They are really probably Xylene and Toluene. These are hydrocarbons with very stable benzene rings that take more energy to separate the bonds, and hence do not break until the high compression ratios are reached. Therefore if you put premium in your POS saturn, it will go through uncombusted and have no effect but to lighten your wallet. If you put regular in your 2003 LS430, the car's intrinsic computer will adjust the timing to get proper and maximum detonation. Your HP will not be the rated 290 HP, but probably about 5% less. You will not be able to tell when you are cruising dow the highway in Oregon, because it does not take much additional energy to keep the car moving at cruising speed. You may however be able to tell the difference when you demand a fast takeoff from the stop sign or in order to pass granny's 86 century by accelerating from 40 to 80 with full throttle.
Digressing....... the former is scientific and based in fact., however, many individuals prefer to make decisions based on their perceptions. If you paid $60K for your new LS430, and think that putting gas in @$1.90 will protect it better than putting regular gas in at $1.70, by all means do it, and reap the emotional reward from your set of perceptions. Reality says you can put in any kind of gas and it will perform proportionally to the octane level you purchasedand have no detrimental effect on your Lexus.

My Opinion
Pjeff

[lspower]

ive never tried it yet but im definitly going to try it soon, a gas station by my house sells 101 octane? could i try this just once in awhile? then go back to 93 octane?
i heard its 4$ or so per gallon but i wanna try it

thanks
ryan

[petrojeff]

Sure, why not? Just don't fill up and drive the interstate to DC or something. Use the gas for more sporty driving etc. Man, what a great business, put 15 cents worth of product in a gallon of gas and quadruple the price! Realize, that you will most likely only get about a 5-6% increase in performance that will cost about an extra $30 per tank. Let us know if you can tell any difference or if you have a method of quantifying the difference.

[daryll40]

I hate to admit this, but in some areas I am so darn cheap. I let my '03 LS430 get to near dry, then add 10 gallons of 87 octane, and end the pumping. Then I reinsert my credit card and, with a new transaction, I pumb about 11-12 gallons (till full) of 93 octane. The mixture ends up at 91 octane, which is what is recommended, but I FEEL like I am saving money. My mixture costs the same as "mid-grade" but I get 91 octane instead of mid-grade 89. 89 is a rip-off since it's priced in between 87 and 93. In the big scheme of things this is totally foolish, I know, but it is that mentality that got me into the Lexus financial league in the first place!

By the way, in the days before credit card swiping at the pump, I guess I wouldn't have done this. But swiping twice...once for each grade, while still more cumbersome that just a single transaction, isn't too much work.

[hyperopt]

With all due respect, octane rating in gasoline is a measure of combustion behavior of gasoline relative to the combustion behavior of pure octane(8 chain hydrocarbon) or a fraction thereof. It has nothing to do with the number of primary carbon chain in gasoline nor the amount of potential energy stored within the bonds.

[USLEX]

Motortrend
http://www.motortrend.com/features/n...41/index3.html

Car & Driver
http://www.caranddriver.com/article....&page_number=1

[Shaffer]

I only put premium unleaded fuel in my 90 LS400. One good thing about this is that one of the local supermarket chains (I actually work for the company) - at the ones equipped with the gas stations- every Friday there is a special where you can get premium gasoline @ mid grade price- so that is when I usually get gasoline for my Lexus.

Back when I had my 1995 Chrysler Concorde with the optional 3.5L V6- I always ran regular unleaded in it, until I realized that there was a sticker inside the fuel lid cover that said "mid-grade - 89 octane" fuel recommended. I started using mid-grade and I noticed no difference at all.
My uncle used to drive a gas tanker and he said for me to just use regular unleaded, as it is basically the same. He said they barely add a bottle of octane to the entire tanker full of fuel. Basically it equals the same octane. I still use premium in the Lexus- to be safe.
On the other hand- I have another uncle that will ONLY use premium unleaded in ALL of his cars.

[SRK]

As I expected the Motor Trend article isn't worth reading, and the Car and Driver one is quite good.
What we learn is:
No modern engine equipped with a knock sensor will be harmed by using fuel of a lower octane than recommended.
An engine whose management system has been optimized for premium fuel may produce lower output, and of those, only a few will produce a noticeably lower output.

I use 92 in the Lexus, and 92 in my LT-1 '94 Camaro (whose compression I have raised to nearly 11:1).
Most gas stations are very careful not to dispense a fuel whose octane is lower than that advertised. To do so would be fraud, and that kind of bad press can close an individual station overnight, and do great damage to the brand name. Given that the economics of gasoline borders on "pure competition", and the profit margins are quite small, they tend to be careful about that. I have known lots of folks who drive fuel tanker trucks, and they do lots of things the public probably doesn't want to know about, but regular in a premium tank isn't one of them, according to them.

[stock300]

Here's another article that may be of interest and supports pjeff's comments:
http://www.usatoday.com/money/autos...remiumgas_x.htm

[stock300]

Oops!! That last URL didn't work. This one should. Sorry about that.
http://www.usatoday.com/money/autos/...emiumgas_x.htm

[airahcaz]

Seems like for our Lexus cars, don't go 87 (even though you can without harm), but use next available up, usually 91.

Readers here agree?

[DaveGS4]

Originally posted by ranjankhan
Seems like for our Lexus cars, don't go 87 (even though you can without harm), but use next available up, usually 91.

Readers here agree?

Ran,

I noticed you've pulled up several old threads (this particular one isn't so old) to ask the same question. As you're finding them with search - try reading the posts! There are MANY threads that answer your question where members have been debated this topic ad nauseum.

[airahcaz]

ya, tried searching, but mostly debates, no majority conclusions. Mostly accept GS is not a good gas car, and premium grade gas is a waste.

My other question I am trying to research is how the LS430 gets such better mileage than the GS? I also notice that my car won't 'go' in low gears, unless my foot is on the gas, whereas the LS cruises to a stop, mine is almost fighting to go to the next gear, I guess cause the GS takes advantage of higher RPM to be such a fast car.

[DaveGS4]

Originally posted by ranjankhan
ya, tried searching, but mostly debates, no majority conclusions. Mostly accept GS is not a good gas car, and premium grade gas is a waste.

My other question I am trying to research is how the LS430 gets such better mileage than the GS? I also notice that my car won't 'go' in low gears, unless my foot is on the gas, whereas the LS cruises to a stop, mine is almost fighting to go to the next gear, I guess cause the GS takes advantage of higher RPM to be such a fast car.

All the threads I've read are slanted the other way, with one or two people arguing that cheap fuel is OK and everyone else sticking with Lexus' recommendation of premium fuel. GS is not a fuel efficient car... want that, get a Prius .

Are you comparing your GS400 to your parent's LS430 or some other LS? If you're comparing the GS400 to LS430 they are two different engine versions 1uz vs 3uz.

Interesting that GS430 mileage is 18/23 vs LS430 18/25. I'd suspect gearing in the GS might be taller/more aggressive impacting the highway rating.