Gas Octane

I bought a new 2008 Lexus ES-350. It has the same engine as the Toyota Avalon, with the same compression ratio. Lexus recommends premium for my car whereas Toyota recommends regular for the Avalon. With the Avalon, horsepower allegedly increases to 280 when you use premium.

I asked the Lexus Service Manager if premium was really required. He said that the transmission wouldn’t work properly if I didn’t use premium, which made no sense to me. Is premium really required for my car? If so, what octane rating? Sometimes I fill up one half 93 octane and one half 87 octane. Is this a good idea?

Why do people buy expensive cars and then cheap out on the few extra cents to put the gas the car needs in. If you want a cheap car, buy a cheap car.

I agree with tardis. You bought a lexus and can’t afford the fuel recommended by the owner’s manual? Trade it in for a Corolla. Maybe someone who can afford to drive the Lexus will buy it.

If the word the owner’s manual uses is truely “recommended” and not “required”, then you can use regular albiet possibly at some compromise in performance.

If it says “required” then I would recommend against it.

It is possible that the engine has been “detuned” for use in the Avalon via the chip. A suttle change in the ignition timing curve could have enough impact to affect preignition.

If the manual only “recommends” premium then it probably isn’t a must. You could try a lower octane and if you experience no problems (knocks/pings) then it likely won’t be a problem. Any knocking or pinging, though should immediately signal a need to increse the octane.

BUT, I have to wonder if you’ve ever done the math. (This is only somewhat related to the above post - why buy real crystal and fret over the cost of the wine?) If you figured the actual cost difference between 87 & 93 you’d likely arrive at fairly insigificant difference, especially when compared to the value of the car.

The thing about the transmission doesn’t make sense to me either unless maybe it has something to do with all of those complicated kinds of interactions between different sensors - so I am skeptical, but wouldn’t rule anything out.

The service manager likely does not know what he is talking about. It has nothing to do with the transmission.

You need to read the owner’s manuals. When it says “requires” premium, then you must use it or risk long term engine damage. If it says “recommends” premium, then it is saying you will get better mileage and power using premium, but the engine will be able to adjust to prevent engine damage.

Assuming you have a choice, remember that if you choose regular you will have reduced power ahd mileage. You might (it varies) loose enough mileage using regular that you could have used premium for the same or less total cost.

If it says you need premium, then doing the half & half thing is not a good idea. Otherwise it just means you are compromising, but no harm.

Maybe has something to do with adaptive shift points.

I tried an experiment with my wife’s 2006 Sienna with a 3.3 V6. The 3.3 was replaced with the 3.5 V6 in the 2007 model year.

The V6 in the Sienna was rated at 211 HP for that year, compared to the Lexus V6 it may have been detuned to run on regular. To summarize, there was no change in mpg between regular and premium gas.

Ed B.

Perhaps, but it still sounds like processed bovine feed to me.

I’m always open to new knowledge via technical explanations.

Yes Lexus! Yes, higher octane fuel! Spend the extra, it’s OK! It’s the cheapskate who pays for the most for repairs.

This has been discussed at length in some Lexus/Avalon boards. The engines are basically identical, and if the manual says ‘recommends’ you can try it with no problem, other than slightly reduced performance. I was in the same situation in my '96 ES300, I tried regular, saw NO decrease in mileage, and noticed NO difference in performance. That was 9 years ago, it’s still going strong.

I asked the Lexus Service Manager if premium was really required. He said that the transmission wouldn’t work properly if I didn’t use premium

That statement right there would send me to another dealer. The guys an idiot.

Wife owns a 07 ES-350…and yes it requires 91 Octane. You sure the Avalon doesn’t require premium. I seem to remember that when we were out test driving that the Avalon DID require premium. My 4runner with the 4.0L requires 91 octane.

Put whatever grade of gas you desire to into your tank. Nothing will get damaged. Nothing will happen to the transmission. If you’re looking to save money, and you burn regular and it is supposed to have high octane, the knock sensor will retard the ignition (it’s all done electronically, not mechanically) so your fuel milage should go down, way down. If the engine is designed to burn high octane, personally I’d use high octane. The only thing for sure you’re bound to get on this board is as many differenet opinions on the subject as people who post replies.

87 octane minimum recommended for Avalon, with premium recommended ‘for improved performance’. See’s%20Album/avy1.JPG/photo/v./photo.jpg

If during the warranty period, something (usually, expensive) happens to that engine, and the car maker finds that you have been using non-recommended fuel (octane), and he determines that the damage was from that fuel, those engine repairs could all be on YOUR “dime”. Of course, that could never happen…or, could it?

From the website comes the following warranty information that is part of the ES brochure:

2008 LEXUS ES 350 Warranty

  1. Ratings achieved using the required premium unleaded gasoline with an octane rating of 91 or higher. If premium fuel is not used, performance will decrease.
    See attached. I don’t have the owner’s manual myself. However, “recommended” and “required” do not (normally) mean the same thing. So I am not sure why the brochure would “require” AKI91 and then allow as how you might not use that. I would ask Lexus customer service about that.

Using lower octane in engines that require 91 octane or higher will cause knock (fuel pre-ignition). One would hope that the knock sensors can compensate by reducing engine performance until the knock stops.

Mixing high and low octane fuel is not a solution because the two fuels do not blend uniformly. You would still be injecting some proportion of low-octane fuel, and that fuel would still be more prone to pre-ignition.

Regarding transmission performance: This makes sense. Theoretically (I don’t know this car), the engineer could design an engine management system that would adjust transmission shift points in order to reduce the engine speed when knock is sensed. You would notice a change in the car’s shifting behavior. You might notice this as an immediate response to knock, and you might notice a longer-term adaptation of the transmission to a persistently lower performance mode of operation.

On the other hand: To be fair, some people use lower octane and really never notice any difference, perhaps because they never travel heavily loaded, never demand peak performance, or they live in temperate areas where engine cooling is not an issue… or because they’re oblivious to the fact that their engine is knocking.

So, if you are not yet sold one way or the other based on these postings, have a heart-to-heart talk with your service manager. Explain your driving habits and get his or her take on it one more time.

If the engine has the same compression ratio as the Avalon, it should run fine on regular.

Try a tank of straight 87 octane regular gas and evaluate any differences yourself. Do you detect any loss in performance during full-throttle acceleration?? Can you detect any “ping” or “spark knock”?? If you can not detect any difference, then you are wasting your money on premium fuel. If you can not detect spark knock, then it is not severe enough to damage your engine. It’s as simple as that.

I have never seen an “unleaded fuel only” engine that was damaged by detonation. The difference between 87 octane and 92 octane is simply not enough to blow holes in pistons as some may claim. A well-tuned turbo or super-charged engine MIGHT be pushed near the limit, but a standard issue street engine, don’t worry about it…Compression ratios in the 9.0 to 9.6 range will run fine on regular. At these compression ratios, damage from detonation is not an issue…

The car is designed to run on 91 octane. But it’s safe to run on 86 octane, but with decreased performance. The engine anti-knock sensor will detect knocking when running on 86 and retard the timing.

These days compression ratios alone are not entirely relavent when it comes to dermining what fuel requirements are. Some direct injection engines have compression ratios as high as 12 to 1, yet will run fine on 87 octane. My 1974 Triumph TR6 requires 91 octane or better, but only has a compression ratio of 7.9 to 1.