I appreciate the clarification…
Found this article that pretty much says it all:
http://www.usatoday.com/money/autos/2003-07-30-premiumgas_x.htm
This topic was discussed at very great length on another Car Talk forum. I researched well and feel the timing retardation by the main computer is more than adequate to adapt the engine to 87 octane fuel. The only worry might be extended travel at highway speeds–for mostly city driving just doesn’t matter. I tried a tank of each grade in my '08 RX and found that the lower gas mileage for regular and mid-grade pretty much wiped out any savings from foregoing premium. Bottom line, better performance w/premium vs. at most a few cents a tankful cheaper w/regular means I always use premium.
As Tom and Ray have noted, any modern car’s computer will retard the timing to easily and safely compensate for lower octane gas, so the only real consideration is performance and mileage. I bought an '08 RX and tried out all three grades, with a full tank of each. Performance was noticably better with premium, as you might imagine. Most importantly, though, was that the mileage vs. cost per gallon worked out pretty much as a wash–premium cost more to fill up the tank, but I got much better mileage, so cost-per-mile was about the same for all three grades of gas. Bottom line, then, is that I always use premium.
When I was in college back in B.C. (Before Computers), one of our professors gave us a surprise test question: “what is the name of your textbook’s author and what are his credentials?”. His point was that if we didn’t know what qualified the author to state the things he stated, how did we know his statement were valid?
So, who is James R. Healey, and who are his technical sources? I see little in this article but opinion. No footnotes to verify information (and put statements back into the context from which they came), no technical data whatsoever. A statement from the API engineer that says he and his wife get by on regular, but nothing saying whether he feels all cars can do so. A statement from Porsche that they design theirs car to run on all fuels, albiet with some compromise in performance…a statement which I believe, but that applies only to Porsches.
The articke is not a bad article, but the author seems to be using out-of-context and vehicle-specific statements to justify a position that all cars can use regular. I personally would be extrememly wary of making a statement like this.
If you do not wish to use premium fuel, do not buy a vehicle that requires it…Do your homework BEFORE you write the check…
FWIW, James R. Healey is the automotive reporter for USA Today, and has had the job since 1988.
I still have doubts. Contrary to his “gist” in his article, it would seem foolhearty for a manufacturer to unnecessarily require premium gas in this age of economic difficulty.
I’ll stick with what the owners’ manual dictates.
This post began in Feb. Old news.
The octane rating of the fuel for your engine is VERY important. The reason for varying octane levels is due to the need to prevent detonation in your engine’s cylinders. Contrary to popular notions about how engines work, the gasoline does not explode in your cylinder, it burns rapidly and expands after being ignited by your spark plug along a wave front. However, if your gasoline is low in octane, it may detonate during the compression stroke, causing enormous pressures that the engine is not designed to withstand. These pressures are so high, that no one has ever successfully measured the highest peaks. Higher octane gasoline allows greater compression of the air-fuel mixture before ignition. Higher compression means greater concentration of energy, so it also delivers more power per stroke. High compression engines are more efficient.
Many luxury car makers offer various types of engines. A Lexus 300 is really a top-of-the-line Toyota and it uses regular gas. Regular drivers use regular gas. Luxury car owners are usually willing to pay more for gasoline, so high-end vehicle makers take advantage of this to design high-compression engines with higher output. You can have an engine from the same basic family with higher compression by making only a few changes, but they are very important changes.
Without going further into the physics, or how octane levels are determined, take my word for it, you should use 91 octane or higher in your high compression RX-350. On the other hand, there is no benefit to car owners in putting premium gas into a regular engine. There are people who think there is some extra power to be had, but their isn’t, since their car can’t take advantage of it anyway. No need to go overboard on your car either, but sometimes 91 isn’t available, and you have to use 92, not 90. It won’t run better on 93, for example, because the compression ratio is already determined by the piston and cylinder.
Incidentally, there is a knock sensor on your engine that can detect detonation, and the engine can protect itself against damage by reducing power. But it could fail, especially if it is being called on constantly, and that’s why they won’t warrant your engine against detonation damage. Detonation damage can’t be concealed, so it’s an easy thing for them to see.
None of this applies to diesel engines, by the way. The diesel actually deliberately detonates, but it uses a much heavier and less volatile fuel that is sprayed into the cylinder at the instant of maximum compression, thus preventing detonation too soon. This is why diesel engines are so heavy and so noisy.
Page 433 of Lexu rx350 owner’s manual:
“If premium gasoline is not available: If 91 rating gasoline can not be obtained, you may use unleaded gasoline with an octane rating as low as 87 (Research Octane Numper 91)”
“If your engine kocks: You may occaonally notice light knocking for a short time while accelerating o driving uphill. This is normal and there is no need for concern”.
It seems to me regular gas is ok and will not affect engine reliability unless you notice the engine knocks also in normal driving and under light acceleration.
So, if car is not pushed by heavy acceleration, uphill, fully loaded, towing, etc., it seems to you can use regular gas.
I also read that hot weather is more likely to generate knocking and cold weathe less likely.
Before I read that I occasionaly put a tank of gas to see if I could hear knocking, I did only if on purpose I accelerated hard but only very light and very briefly.
Now that I read the manual I will use regular always, unless I will tow a trailer, fully loaded uphill with hot weather. No more wasting money as my car is driven lightly.
Hope this helps.
@Hothardtruths1 After seven years they should have made up their minds or may not even still have the vehicle.
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started thread in feb. picked up again in sept and poster was chided for being an idiot. now 7 yrs later idiot #2 chimes in? HOW the heck do you even dig up a 7yr old thread? must be the holiday booze
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I at first wondered how this beating a dead horse topic continues to surface. Then I saw the date (February 2010)! “Recommended” can be a slippery slope in litigation. “suggested” to “required”. I will never understand people willing to risk thousands of dollars damage to an expensive vehicle to save pennies per gallon on fuel.
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