stiles_s

This is one where I'd say we can't really know better than the engineers.

My '07 says "Premium Unleaded Fuel Only" under the gas cap. That's un-ambiguous.

The owners manual says 91 octane or higher everywhere. I don't see any reference to using lower octane temporarily.

We don't know for certain that the engine tuning is exactly the same across all years of the VVT-I GX's.

And, yes, modern cars know how to reduce timing when they detect knock. But, some react faster and more accurately than others. If they react too slowly, damage can happen. Don't think you'll be able to "hear it if it's a problem". The wrong fuel can also mess with things like oxy sensors and catalytic converters.

At the end of the day, we can all make whatever decision we want re: fuel. I'm going to go with Lexus' clear guidance on this one. Not because I want 3 more HP, but because I don't want any expensive repairs down the road. From my perspective, anecdotes on the internet along the lines of "I've never had a problem", or "I've never heard of a problem" aren't going to make me want to take a risk. Yes, Premium is expensive. So is replacing cats, oxy sensors, or repairing engine damage.

Just my $.02.

RCsGX

The engineers say to use a higher octane regarding lowering emissions IE: LEVII-ULEV, SFTP requirements, it has NOTHING to do w/ keeping the engine safe. Our 2uzfe VVT-i engines are not high compression engines (10.1:1) so there's no need to use a higher octane gas. This 87 vs 91+ octane debate has been beat to death over the years regarding the 2uz-fe engine.



I pulled the info straight from the 2006 owners manual.



"We don't know"...speak for yourself. Tuning is through the ECU. '05-'09 use the same part number ECUs. Read through the different year repair manuals like I've done before. ALL of the engine specs from '05-'09 are identical. All of the engine parts are interchangeable and share the exact same parts numbers from the ECU, to the oxygen sensors, to the knock sensors, to the cam position sensor etc.

The only changes between the '05-'09 models are exterior and interior changes.




Again, using a higher octane gas has nothing to do with reducing engine damage as you say...you will not be "risking" your engine using 87 octane. Regarding our GX it has to do w/ emissions plain and simple. Stop trying to scare folks w/ this nonsense of using a higher octane will somehow protect your engine from damage. You want to use 91+ that's your choice. Will any harm come from that, nope, will any good come from that, nope.


Seeing you own a Porsche, even Porsche recommends premium but do you think their engines will self destruct if you use 87 and not 91+?

"All Porsche engines are designed for premium, too, but it's not available everywhere. Our cars must be able to drive all over the world, and so we are able to run on regular," says Jakob Neusser, director of powertrain development at Porsche's research and development center in Weissach, Germany. "You don't have to feel that a mechanical problem or anything else will happen using regular gas, even in the highest-performance, regular-production Porsches."




FACT is you are perfectly safe using 87 octane in any '03-'09 GX PERIOD!

Have fun debating, /unsubscribed....

lesz

That is the point that some people want to conveniently ignore/dismiss.

But one of the things that I've learned over the years is that it is virtually impossible, once people have been wasting money on something for years, to convince them that they have, in fact, been wasting money. Regardless of how many facts are presented and regardless of what the science is, it is a part of human nature not to want to accept the fact that one has been wasting money.

Thus, the value of this kind of discussion is for those who are thinking about how they want to spend their fuel money for the first time and who still have an open mind and are not locked into one way of thinking.

stiles_s

EDIT: I just read the initial post in the thread, where he's asking about a 2004. Though I'd enjoy learning more about our engines and octane requirements, the point is moot for '04s, no? Clearly OK w/87 given the owner's manual and the pre-VVT-I engines, based on my understanding.

If you're game, read-on. Otherwise, please accept my apologies for being OT.

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RC, I'd love to better understand what makes you so incredibly sure.

Feel free to ignore if you want the last word, or engage and teach me something . Looks like I touched a serious nerve. It's funny that you guys are suggesting that I'm the one who's closed minded. Seems you're convinced that Premium fuel is a hoax designed to extract money from fools.

My understanding, based on decades of car geekery, is higher octane allows you to safely run a more aggressive ignition timing curve and therefore tune for more power. Back in the old days before knock sensors, you could do serious damage to an engine if you advanced the timing too aggressively. Do we agree on this, or is this fiction as well? I hand programmed a custom ECU for my old Miata Turbo system, and it was tuned for a very specific octane range.

Whether you're going to experience knock isn't just due to compression ratio, by the way. It's a combination of compression ratio and ignition curve. You could tune a 10:1 engine to run only on Premium, or a 12:1 engine to run only on Regular. Throw in boost and you have another factor to consider (I know our GXs aren't boosted, btw ).

Knock sensors allowed car manufacturers to tune optimistically for higher octane and better quality fuel, and reduce timing if they detected knock. The early systems were slow to respond and so there was a non zero chance that you could do damage if you ran lower octane fuel. One of my earlier Porsches still pinged pretty badly on premium fuel when under the right load. Was nerve wracking Did it do any damage? I'm not sure. The car was incredibly "happy" on 94 octane from the local race fuel supplier, but I rarely ran it because of cost. You're probably right, Porsche probably built in safety measures to avoid engine damage. Probably fine. or, they just knew it was super unlikely the would blow up under warranty...

Can you provide a reference where Lexus or Toyota engineers say the premium fuel was for ULEV requirements? I'd love to see it. Does this mean the GX runs "dirtier" on 87 than 91? In what way? Does it create more work for the Cat? if so, could that explain some of the oxy sensor and cat failures we've seen? Do we know for sure?

Great to know that all of the ECUs are exactly the same part number in VVT-I GX's. I think, by your reasoning, this means they all contain the same tune? Manufacturers update programming in their ECUs all the time. You're 100% confident that Lexus hasn't done this? My last M3 had at least 3 different ECU flash updates from the dealer in the year I owned it.

I'm not trying to tell anyone what to do. Just want to learn. I agree that it's "quite likely" that the GX is perfectly "fine" on 87. Might run a bit dirtier (re: your claim regarding ULEV), and likely makes less power. the modern ECUs in the Lexus' are probably "fast" enough to pull back timing if they detect knock (preignition) before it becomes a problem.

Can we agree that the GX ('05+) is tuned for Premium? or are you arguing something different? I'm pretty certain Lexus would have loved to allow users to run Regular fuel in their GXs. Buyers are pretty put off by Premium fuel being required.
Can we agree that the ECU is likely smart enough to pull back timing if it detects knock? And, that when timing is retarded you lose power?
Can we agree that Premium fuel won't damage anything but perhaps one's wallet?

I've done 90k in my GX since new. I played around with 87 for a few weeks a few times. I noticed little difference. It felt a little sluggish but it could have been placebo. I never noticed knock. That said, I put my GX under a ton of load, sometimes at high temperature. All cases that can trigger knock. I don't mind a little safety net.

Peace.

lesz

After doing some further reading, I believe that the reason for a change in wording in the fuel recommendation in the 06 GX manual from what the 05 manual said is a change in the EPA's rules regarding the requirements to qualify for the higher emissions rating. In 06, those requirements changed, and to qualify for the higher rating, Lexus had to say that 91 octane was required, and 87 octane could be used temporarily, and they could no longer say that 91 would maximize performance, but 87 would be sufficient.

RCsGX

Yes I know...I've been saying all along that it has to do with emissions and nothing else. You won't damage or hurt your engine in any way / shape / form / fashion using 87 vs using 91+ octane gas.

Chemee

I've only ever used 87 octane. Confirmed with local dealer that this was ok when I bought my GX. Haven't had any issues.

ChiTownGX

I have a 2005 GX that I have been running 87octane in for the last 6 years. I tow a race car in the summer months quite a bit and have always used 87 without problems. I am curious why you say that you need a higher octane when towing.

RCsGX

Because depending on the weight of your load some 2uzfe engines will start to ping a bit whether it's the newer VVT-i or not.

spport

Thanks for all the evidence you put into your post RC and the manual pic Lesz. I have an '07 and my manual says premium only but now I understand why. Thanks for the work guys.

ChiTownGX

I guess I could see that with a load nearing the 6,500 lb limit. So far, with about a 4,700 load, I have not had any problems. Filling with Premium when towing would not be that big of a deal anyway.

Thanks for the input.

RCsGX

It's not a big deal because you're GX isn't pinging when towing. Several Tundra / Sequoia / 4Runner owners have had pinging problem when towing too and they switched to premium and the pinging went away. Some only used 87 when towing and don't get any pinging. If my engine were pinging I would up the octane.

Later tatter chip......

https://www.youtube.com/watch?v=VRnE...youtu.be&t=42s

cassman

I am new to this site, more so I am a new and VERY HAPPY owner of a 2004 GX470 with only 66,000 miles on the odometer. Yes a one owner and very pamperad vehicle, but in reading the owners manuel it stated that the truck should be filled with ONLY premium gas with a octaine level of 91 or higher. So is this truly necessary for this vehicle ? And if so why ? Your personal experience's or expert knowalge is much appreciated !

ALAN553

I believe is says recommeded? That being said...regular is the gas of choice, why Lexus says this is unknown. The 4 runner, same engine recommends regular. Most here will tell you that there are no benefits, performance, MPG etc. other than less money in your wallet.

UpStarr

Premium Unleaded Fuel Only. See Owners Manual. Why do we continue to challegne this? <--rhetorical question



OK...Now lets look at the OWNERS MANUAL. The key word here is ONLY


Take a look at the link below:

" MPG Crappy"
https://www.clublexus.com/forums/gx-...pg-crappy.html

87 octane and you wonder why your MPG is "crappy"

cassman,
congrats on the new ride!