Premium Fuel...

[chimchim]

I just rechecked my 2004 RX330 manual at it does say 87 minimum, 91 recommended.

I'm switching to 91 and resetting the ECU.

I'm hoping to show the difference someday with a scantool showing ignition timing... unless someone else better equipped can do it first.. HINT HINT.

[TunedRX300]

On Toyota's website at toyota.com there is an FAQ for owners and it says this about the MINIMUM

recommended octane for each 2005 Toyota engine:

http://i5.photobucket.com/albums/y189/mastertech/.min.jpg

I hope this helps you guys understand that when Toyota recommends 87 octane, iridium spark plug changes every 120,000 miles, air filter changes every 30,000 miles, etc.  that those are all just MINIMUM recommendations & service intervals, not necessarily the best recommendations and intervals to follow for maximum reliability, durability, drivability, etc.

Likewise the owners manuals of nearly all Toyotas going clear back to the 1970's say: "Use 87 octane OR HIGHER."  That's Toyotas way of saying 87 octane is the MINIMUM allowable octance and not necessarily the best octane to achieve optimal engine reliability, durability, drivability, etc.

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Let's not play the guilt card here. There is already enough Lexus owners who were led to believe 91 Octane is the minimum by oil companies. "Premium car MUST need premium fuel"

Octane rating of 87 is within Toyota's official recommended range - warranty is honored by Toyota.

Now on topic: how does the octane rating of fuel affect tranny's ability to shift smoothly?

[monarch]

wwests original post was about whether or not using 91 octane would help alleviate the hesitation up acceleration. It should in 3 ways:

1. Using 91 octane prevents the engine electronics from retarding the ignition timing. Retarded ignition timing in any vehicle causes a longer lag in throttle response = more hesitation upon abrupt acceleration.

2. Using 91 octane provides quicker starting, smoother running and more instantaneous throttle response in any vehicle because it burns more smoothly and evenly.

3. Most brands of 91 octane have higher amounts of engine cleaner / detergent additive to keep intake valves and fuel injectors cleaner which in turn reduces the tendency of an engine to develop a hesitation upon acceleration.

[TunedRX300]

Monarch, See what this SAE expert say about #2 and #3 reasons you posted in this USA Today report.

Premium Not Necessary Better

This link is posted by a member in the maintence thread, I select a few quotes from Nissan, Toyota, SAE and FTC experts in the article for those who are too lazy to click .

""I personally use regular even though my owner's manual says you'll get better performance with premium," says Lewis Gibbs, consulting engineer and 45-year veteran at Chevron oil company. He's chairman of Technical Committee 7 on Fuels, part of the Society of Automotive Engineers (SAE) Fuels & Lubricants Council. Gibbs knows gas."

"Premium, in fact, sometimes is worse fuel than regular. It resists knock because it's harder to ignite than lower-octane fuels. As a result, some engines won't start as quickly or run as smoothly on premium, notes Gibbs, the SAE fuel expert.

High-test does have a potential fuel economy benefit. It is slightly denser than lower-octane gas, meaning there's a little more energy in a gallon. But the small difference is hard to measure in real-world use, and that same density can contribute to undesirable buildup of waste products inside the engine.

No data show that engines designed strictly for regular run better or longer on premium.

The Federal Trade Commission, in a consumer notice, emphasizes: "(I)n most cases, using a higher-octane gasoline than your owner's manual recommends offers absolutely no benefit. It won't make your car perform better, go faster, get better mileage or run cleaner."

There is "no way of taking advantage of premium in a regular-grade car," says Furey.

"There is no gain. You're wasting money," insists Jim Blenkarn, in charge of powertrains at Nissan in the USA.

"No customer should ever be deluded into thinking there's any value in buying a higher grade of octane than we specify," says Toyota's Paul Williamsen, technical expert and trainer."

[wwest]

I lived, and drove, in the days before ECU controlled engines..., LONG BEFORE!

Back in the stone ages, the time of carburators, mechanical ignition points and distributor caps...

We knew that if we started up a long incline and the engine started pinging, knocking, we were "lugging" the engine (operating well below the engine's best power level/RPM) and we therefore downshifted immediately.

So the engine/transaxle ECU "commanding" a double downshift (assuming that's what's happening) is a perfectly logical thing to do.

When I got older and decided that flying was in my blood I was taught to ALWAYS run our recip engine on the rich side because in an airplane "pinging" is not so easily heard and in short order we would have a failed engine.

So....

If the knock sensor "says" the engine is pinging, you (or your ECU) can...

A. Enrich the mixture.

B. !Removed! the timing.

C. Downshift.

D. Decrease the prop pitch.

The correct answer is:

A or B or C

Or:

A or B or D

I can readily see where the engine/transaxle ECU might become quite thoroughly confused, befuddled even, with all those choices. Quite a decision "tree" for your average "bright" programmer to solve.

Sure am glad I couldn't adjust (didn't have to think about) the mixture or the timing on my old 56 Ford.

PS: Pinging can still occur even with the timing fully retarded.

[chimchim]

Good info... I think that's a very plausible explanation as to why the RX has that double downshift hesitation. As soon as I use up the current tank, I'm going to switch to 91 and see.

[archerIII]

I am of the camp that uses Premium fuel in my RX300. I don't think that Lexus would recommend it if there wasn't a reason and I doubt there is a conspiracy with the oil companies. Recommending Premium can actually turn off a lot of customers. Who wants to spend an extra 30+ cents a gallon?

My opinion goes back to my first Toyota V6 in a 1995 Camry. It did not like Regular Fuel, period. It hesitated and stuttered without Premium. It took me a while to figure this out since I did not initially read the manual. If you are experiencing problems I suspect you have a heavy foot as I do.

Is that to say that a Mid Grade would not work? You'll just have to try it, and also try different brands. There are a lot of variables; season and weather,altitude, driving style, vehicle loading, fuel formulation, age or variations in the particular vehicle, etc..... All of these variables conspire to create a internal cylinder pressure and temperature that could cause detonation with a particular octane of fuel.

[SeaDuck79]

For those of you in either camp, would flashing the ECM be of some benefit when changing to the higher octane gas? Wouldn't it learn about the new octane on it's own?

[greekgod]

when i got my rx330 1.5 months ago the sales rep told me that 89oct is fine been filling up ever since with no hesitation problems..

[chimchim]

when i got my rx330 1.5 months ago the sales rep told me that 89oct is fine been filling up ever since with no hesitation problems..

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I'm having major doubts as to you even understanding this thread, if you even read it.