High octane fuel is required in high compression engines, but this is not a high compression engine. Most BMW's for instance run very high compression, so when they say "Premium Required", they mean it. Turbocharged engines, even more so.

Lexus recommends premium for the gx simply because it will ever so slightly reduce emissions, and it will allow the gx to hit it's advertised power output numbers. Running regular unleaded will slightly reduce power (due to timing retard) and slightly increase emissions. You won't significantly notice any drop in mileage, and the power drop will be barely noticeable.

I run regular unleaded exclusively, no problems.

 

I run 87 in my '04 exclusively, but with an '05+ vvti engine, and while towing, I'd probably use 91 octane. Not because I think it would hurt anything, but any extra power is nice when towing.

 

Actually even with same Octane fuel, they are different between brands. Our cars like Shell brand.
Ethanol contents play a role too how engine performs.

 

I tried 87 in my '08 when I first bought it and it pinged like crazy under load. I could hear it inside the cabin. I switched to 91 and it went away.

 

I am gonna start using the 87 stuff.

 

Around here, all gas is the same to start, it's the additive/cleaner that is different. The tankers carrying the top tier brands have that company's proprietary cleaners added at filling, shell, BP, Exxon and even Costco etc. so octane is uniform here, 93, 87 and a blend to produce 89.

 

I've got some more info on this with my 06. I make regular drives from Massachusetts up into the center of Vermont as we have a second home there. As most of you know the cruise kind of stinks on these vehicles and will shift down at the slightest hint of slowing down when driving on hilly/mountainous terrain. When running 93 octane instead of 87, I can set the cruise at 75mph and the car will never shift down to get up an incline, just cruises along. Its the opposite with 87, downshifting many times on the inclines.

MPG is a tiny bit different, but not that noticeable, just the performance. I would say if towing/driving through mountains, etc. step up the octane a bit. Maybe 89 is all it takes.

 

reason - loss of power. the way I noticed it - there is a large hill around here. when I drive in cruise control up the hill, at around 60mph, with 87 - the transmission would downshift TWICE, on 91, the transmission would downshift ONCE.

 

If you plan on using a lower grade fuel then you should put in Sea Foam a couple of times per year. Sea Foam is good stuff.

 

I have a 10% grade on the way home from work. It'll downshift to 3rd in order to maintain 55mph. When running premium the GX goes up the hill at a slightly higher RPM and feels like it isn't struggling as much.

Running it in cruise control (traffic allowing) is crazy - it can't maintain a gear. Sometimes it'll drop to 2nd @ 4500 rpm...

Chip H.

 

i don't think octane has anything to do with detergent additive???? Octane has more to do with compression, burn ability, heat , etc. Top Tier Gas has the same detergent packages across all three octanes.

 

In Canada they certainly market the higher octane grades as having additional detergents/additives, no idea what's actually in any of them though.

Edit: can't find what I'm looking for, retracted.

 

From Shell Canada

I see all brands collecting fuels from the terminal - so aren’t all fuels the same?

There are actually two key components to a gasoline—the base fuel and the additive system. Base fuel quality is generally the same in an individual terminal. However, Shell blends a unique and patented additive package with enriched Nitrogen into all three grades of Shell gasoline before it is dispensed from the terminal. The Shell Nitrogen Enriched Cleaning System contains a patented formula, exclusive to Shell that cleans and protects intake valves and fuel injectors from gunk left behind by lower quality gasolines. No other gasoline protects better!

 

Just got a used GX and there is a sticker in the gas door that says to use super unleaded only? Is there a problem with just using regular gas all the time?

 

Welcome, rhapke!

This is a controversial topic, and not just for GX owners, but anyone who has a luxury car that "requires" premium fuel.
I have researched the topic myself and came to a conclusion there is no black or white answer. I could not find any evidence of regular fuel killing the 2UZ motor. Some state that lower grade fuels may cause engine pinging. Some report driving over 100k miles on regular fuel without any problems. I have tried short and long trips with both premium and regular fuel in my GX's tank, and have not been able to notice any difference on how the engine ideas or performs, gas mileage or acceleration.
There are folks with an opinion that engineers are recommending certain fuels for certain engines for optimal performance. I agree with that. If you are a purist and want to do things by the book, then you should use premium fuel only.
Now how do you argue with those owners of 2UZ motors in 4Runners, Tundras and Sequoias that are never told to run premium, and owners manual stated regular fuel is recommended? Same engine, but because the truck costs more, you need to buy premium gas? I agree here too, that's a rip-off. Unless engine tuning of the GX vs Tundra/Sequoia/4Runner is different, then I stay corrected.
Still, with a 11-year old truck with over 120k miles on it, I choose to use regular fuel.
Hope this helps.