Just trying to verify if I need to really buy Premium gas for a new (used) 2015 is 250 sedan I am buying today.

 

Yup you definitely need premium gas!

 

Yes, it is directed by the manufacturer

 

Yes, it is SPECIFIED by Lexus' engineers due to the high compression ratio of the engine. It is not specified for fun performance reasons nor fuel efficiency reasons. Using lower than specified octane gas WILL immediately downgrade its performance, soon start to cause detonation (spark-knock) and eventually damage your engine or components of it.

Don't know why there are different octanes? Here's the Wikipedia article. The first couple of paragraphs say it all: https://en.wikipedia.org/wiki/Octane_rating

 

You'll be fine with E85 or diesel. Jk yes you NEED premium

 

Anyone else thinking this should be added to the FAQ thread?

 

Water is fine.

 

Run the 92 octane. You'll really feel the difference when the VTEC kicks in
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There are numerous articles and even youtube videos on such topics like does the higher premium octane gas give that much better and noticeable difference in performance or fuel economy? Well alot of them came to the same conclusions, that for most non-performance cars, putting in premium fuel actually hurts the gas mileage and doesn't affect performance at all. So this being for an is250, i would say using 87 is good enough for it for normal daily driving. After watching all these documentaries, i switched from 91 to 87 in the wifes is250 and its been well over a year now and still runs great! i used to use 94 in my is350 and since switched down to 91. It makes no difference for such cars that are not performance oriented. Now when i had my ISF, i only fed it 94, and thats because it is more of a performance machine.

Search on google and youtube and you will get your answer and put in what you think is best after watching.

One example that comes to mind is that companies advertise that the premium has more cleaning agents, well they did testing in labs on regular to premium gas and they found they both have the same amount of agents!

 

if you really have concerns like this before buying a Lexus... Don't buy it.

 

I'm not going to push you one way or the other. However, I would use the octane rating recommended by the manufacturer of the vehicle.

If all your driving is in the city, and you drive like a granny, you might get away with it. Keep in mind that cars these days have built in safety zones. Different retailers have different additive packages. Some have more some have less. Quality of fuel is not always consistent either. You can always get a bad batch of fuel. If you decide to run on regular, and you happen to get a bad batch of fuel, you may have some running issues. Hell, you can get into running issues on 91. But if I'm running 91, I know that the computer has enough of a buffer to retard timing if it needs to.

ive only watched a couple of documentaries on this. The few I've seen, they've done testing on cars that have a recommendation of 87. They're econo cars basically. So no. They won't make a difference in power on cars like that. One or two tanks of fuel and a test don't always show the downsides. our IS are actually considered performance machines. Even a 250. They're all designed to be luxury sport sedans. Try low octane on a modern n/a BMW. It'll be fine for a little, but it'll hate you for it. The ecu actually records and calculates the octane of the fuel in bmws. I've seen people go to the dealer with blown engines asking for warranty, and it be denied due to the ability to prove by the cars ecu that the wrong fuel was used.

But hey, I'm crazy haha. I fill up at the same pump, at the same station every time. I'll deviate if necessary, but if at all possible I'll use the same pump at the same station. Like I said, I'm just a ball of crazy.

 

And please do the exact opposite of this person here unless you'd like to deal with costly maintenance down the line and future engine knocking.

If you drive 15k miles a year on average and get 20mpg, you fill up like what, 40-50 times a year? You're spending like 200-250 more on gas every year assuming 91 is .30 more. That amount shouldn't be a concern to you if you're purchasing a luxury vehicle. Treat your car well and it'll treat you back.

 

The IS 250 is tuned to run on 91, so why would you risk putting something lower in it? The manual straight-up says you risk damage to your engine by doing so.

Again, I ask why is this not in the FAQ for the 3IS? This question is asked entirely too often and results in the same repeat back-and-forth.

 

This answer could not be more wrong and devoid of any scientific understanding.

You really need to read this Wikipedia article, learn what the effects of uncontrolled detonation (spark-knock) is, and check out what your engine's compression ratio is. Then you may begin to truly understand the reasons why the ENGINEERS who built the engine built it that way only because high octane gas was is commonly available nowadays. Octane rating is not recommended, it is specified!

https://en.wikipedia.org/wiki/Octane_rating

Please stop giving people false information that can potentially damage their vehicle and hurt it's resell-ability.

 

My thoughts exactly.