Originally Posted by 285exp

Considering that the car is 10+ years old with 73k miles on it and has been burning regular the entire time, I think it's safe to say that using regular isn't going to make bad things happen to your car. The engine has knock sensors, and so as long as those are working and you are hearing no obvious detonation, you won't damage the engine. Premium will allow for more advanced timing, thus giving you some more power and greater efficiency, it will be up to you to decide if the extra expense is worth it. You will find some people who say they can tell a dramatic difference and others who can detect none at all. Given that, I would suggest that you just experiment yourself. It won't cost you a bunch of money, just a few extra bucks a tank for premium, and you won't have to depend on a bunch of guys on the internet. In a perfect experiment, you wouldn't know what grade of fuel is in the car and you would be driving an identical route in an identical fashion. If you know what fuel you're burning, then any subjective criteria like engine smoothness and "pickup" may be affected by your perception of how you think it should be. If you think that you should be getting better mileage because you're using premium, it may affect the way you drive and therefore contaminate the results. So, if you really want to have an objective experiment, have someone else fill the car and not tell you what's in it. It would be best to run several consecutive tanks of the same grade before changing to the other, because unless you run it almost completely dry the resulting mixture is going to be a weighted average of what was in the tank and what you put in. In terms of absolute accuracy, you should calculate the mpg manually, reset the trip odo and divide miles by gallons at every fillup. However, just to figure out whether you're getting better mpg, you can simply reset the avg mpg display after every tank, or even only after several tanks of the same grade so you can sort of even out the fluctuations you'll get in normal driving. It may not be exactly accurate, but it will indicate whether one grade gives you significantly better mpg than another. The more tanks you run through and the more consistent you are in your driving the more useful the results are going to be.

Originally Posted by Power6

Not so fast my Kiwi ES brother...we use a different octane rating system in the New World...R+M/2 vs. the RON rating used in much of the rest of the world including NZ. Your 91/95/98 petrol is roughly equivalent to our 87/91/93 rated gasoline ;-) Though not all of the US can get 93-94 octane.

Originally Posted by NZESDriver

Oh, did I not mention I mix it 50/50 with 110RON aviation fuel ?? I guess I forgot...
Every month when I go out of town for work. More kilometres/ L too !

Originally Posted by meadowz06

Here is another perspective. You will lose about 5-10 horsepower also by using 87 octane. My 1991 ZR1 Corvette had a graph showing the difference between 87-91 octane and horsepower. I would personally use 91-93. You will get better performance and ensure that the engine does not ping or detonate. And as others have stated the motor has a fairly high compression ration, so higher octane is beneficial.

Originally Posted by MrShim78

My two cents buy the good gas. its a good engine, give it a proper diet. I use premium on my 97 es and the results are quite good

Originally Posted by 285exp

And once again, we're back to trying it out for yourself to decide if using premium is worth it. That's the bottom line. Don't pay any attention to me or anyone else, find out for yourself, just be objective.

Originally Posted by Power6

Careful now! Though the 1MZ-FE (or any other stock moor) is hardly programmed to take advantage of 100+ octane, but hey good stuff if you can get it. Highly illegal in the states due to tax implications.

My dad was a chemist by degree and worked in that field when I was a young'n. They used to have drums of benzene hanging around his workplace, the guys would fill their tanks with it, he ran his '81 Civic on the stuff. He swore it ran great on the ~100 octane benzene. Burnt lots of valves though but I think many of those CVCC motors did that.

Originally Posted by youngim87

Before I get flamed for posting an already discussed topic on here I want to let you know I did about 2 hours of researching on CL and still cannot make a conclusion on what I was trying to figure out.

So, I proceed with my question: Background info - I recently bought a used, but excellent condition, 2002 ES300 with 73K miles which was driven very lightly by the 1st owner mostly for a work commute. It was driven by a woman in her 60's so I highly doubt it was driven hard and long on a daily basis. I was informed that only 87 (regular) octane gas was used as well as regular motor oil (non-synthetic). The driver's manual calls for the use of 91 octane and I have read on here that the use of lower octane, more specifically 87, would most likely cause some type of knock/pinging due to the faster burning lower octane gas which retards the engine response to the fuel quite a bit. This particular car doesn't seem to have any type of noticeable engine problems, pings, or knocks and drives very smoothly, however, I have only had the car for 3 days so far so who knows what I'll encounter *knock on wood*

My question is: Should I continue to use 87 octane gas or should I switch over to 91 octane gas for the first time in the car's life? I'd much rather put 87 to save a couple bucks at the pump and remain consistent with the previous owner. Any suggestions or experiences would be appreciated (Sorry if that was a long post )