lower octane gasoline

Some vehicles require high octane because the engines have a high compression ratio. High compression engines will not run properly on lower octane fuel and engine damage can result from the use of improper fuel.

Some other engines have more advanced ignition timing to improve performance, and the higher octane fuel allows more advanced ignition timing. The advent of electronic spark advance and now distributor-less ignition allows a much wider range of ignition timing, and combined with knock sensors, the car's computer can retard timing to allow the use of lower octane fuel, with the tradeoff being slightly less performance and fuel economy.

RayO, Do you have an opinion on the effects of premium and regular on how some of the transmission shift on our Lexus's?

I have heard but not read first-hand of a technical service bulletin that recommended using permium fuel to improve transmission shifting on vehicles with delayed shifting. Using premium fuel will apparently help but not necessarily eliminate the delayed shifting.

The answer is that premium CANNOT fix it.

I had a 2002 ES with that crappy trans. Nothing they did (resets, etc) could fix it. When they performed TSIB TC004-03 I felt it was better for a few weeks, but then the hesitation and slamming shifts returned. Such garbage from Lexus/Toyota Engineering is a disgrace. Hopefully, everyone who signed off on that poorly-engineered trans was fired. Those still there who continue to say "No problem exists" should be fired as well.

Anyhow, I have a copy of the TSIB, and it is clearly noted (in a box bordered in RED) on the last page that one should :

"Select premium unleaded gasoline with an Octane Rating of 91 (Research Octane Number 96) or higher ... "

I did that - NG. I no longer own the car .......

How could premium fix a bad engineered tranny???

I don't know for sure. From what I've read, the problem is more with the transmission ECU's programming than the mechanics/hydraulics of the transmission itself. The transmission ECU uses inputs from several sensors, probably including ignition timing.

So using the super duper hi test ethyl gas, I get 14.5 mpg around town. If I change to the lower octane regular, what will my milage decrease to?

In a previous question, I had mentioned how a Maryland Lexus service rep. had recommended I stop using premium ( I had complained to him about my sooty tailpipes and he said using regular would stop sooty deposits)..... well 5000 miles later, the soot is starting to disappear, and my mileage with regular gas seems to have improved, especially in highway driving.

The reason I bring this up is that I had a problem with the transmission: when I came to a stop and then stepped on the gas, the car would hesitate. I brought it to my New York Lexus service rep's attention and he said that this problem could not be solved, I would have to live with it, because of the way the transmission ECU was set. Now lo and behold, I forgot about this annoyance and guess what! Since I have been using regular, the car or transmission no longer hesitates after I come to a stop and want to step on the gas again.

Just wanted to share my experiences with my 2006 GS300 AWD; right now my main gripe is that the car is underpowered, unless I get aggressive with the gas pedal, in which case it downshifts (a lot) and really moves. Another mild gripe, the car used almost a quart of oil in 5000 miles, then I added half a pint and the dipstick reads half full.......... I never had such a quirky dipstick and why does it have to be so long......

How could premium fix a bad engineered tranny???

Some comments on the topic: when I complained about my car hesitating when I come to a full stop and then immediately step on the gas, my Lexus service rep. said it could not be fixed, it had to do with the ECU settings in the transmission. I also complained about sooty tail pipes and he just said it was not important. Then at 20K miles, I went to another dealership with my 2006 GS300 AWD and complained about sooty pipes. The service rep at that Lexus dealership recommended I use regular instead of premium gas.

Net result is that my mileage improved, especially for highway travel, and after 5K miles the pipes appear to be loosing the black soot that was there prior. I never personally cleaned the pipes. Then lo and behold, a funny thing happened, I had forgotten about it until the subject of tranny hesitation was brought up again: My car no longer hesitates after I come to a full stop and want to get moving again.

Other than that I have only two beefs: (1) not enough power, unless I get aggressive with the gas pedal, in which case the transmission is often downshifting, and (2) The dipstick showed I had used almost a quart of oil atfter 5K, when I added a half pint, the dipstick read on the halfway mark; wish the dipstick were not as long and was more accurate.

Pleased as punch

Ray, Does it harm a 05 ES 330 to switch back and forth between premium and regular gas? Lately, I've been considering the price. Al

Check your owner's manual. Lexus is good about telling you if it's perfectly OK not to use premium gas.

Please tell me why people buy luxary cars if they can't afford the gas? It is a LUXARY CAR. It is for people who can afford them.

Frequently, the "premium" recommendation from the mfr is simply to cater to the idea that "I bought a luxury car, it doesn't take anything as PLEBIAN as REGULAR gas".

The whole idea of "regular" and "premium" gas is just so much hooey. "Premium" gas isn't premium at all. It simply is a higher octane gas. That doesn't denote a "premium" fuel at all. There really is no such thing as a "premium" fuel.

So if your mfr states that you may run the car on 87 octane (as Lexus used to do, at least), and if you get good gas mileage (sometimes 87 octane fuel gives better mileage than 93), then who cares?

I don't recall saying that I couldn't afford it. I simply want to know if I can sometimes minimize being ripped off at the pump. Besides, I have read often enough that many people waste money when they buy "premium" instead of using regular. My question was whether there is any harm in switching back and forth, or should I select one grade and stick with it? Now, if buying premium instead of regular for your Lexus makes you feel better, fine. Al

What is a LUXARY CAR?

I have heard that it is generally not a good idea to switch back and forth between grades, but doubt that it is harmful. I believe using higher grade does give you slightly more power, and sometimes better fuel mileage, but it didn't work out to be much different on my 2005 ES 330. I now use 87 octane all the time.

Bob

I switched to high octane (93) for my 2004 ES330 about a year or 2 ago. The increased cost is mostly paid for by improved gas mileage. Some here have said they get about a 1 mpg increase in gas mileage. Based on the onboard computer, my experience correlates.

Also, while the higher octane gas doesn't eliminate the hesitating/jerky transmission entirely, it reduces the problem significantly. But, as the say, YMMV.

It doesn't hurt to switch back and forth between premium and regular gas, but after you have used regular gas, it can take a couple of tanks of premium before the advantage from premium is re-gained because it may take that long for the computer to realize that it is "safe" to advance the ignition timing enough to take advantage of the higher octane.

My recommendation would be to pick one grade and stick to it.

If the car is designed to run primarily on regular fuel, then IMO, it is a waste of money to use premium. On the other hand, my experience with my LS

400 and LS 430 is that I get a performance and fuel economy benefit from using premium, so that cost-wise, it is a wash to use premium, with the bonus of a little more performance from the premium.