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Where I live in NorCal, the difference between 87 and 91 can be $.50-$1.00 per gallon difference. If I use 87 instead of 91 could it really cause an issue?
Also will 87 vs 91 show a major difference in MPG?
I feel your pain. Premium is much more expensive anywhere these days. Shell 87 $2.15 and 91 is $2.95. That's is $.80 more or about 30% more.
do we get 30% more mpg or hp? I doubt that. The similar engine in the tundra runs fine on 87. However, I feel the GX is quieter and 1-2 mpg better with 91 vs. 87.
I've read alot of posts about this. There's a long thread on the gx470 forum too. Some people reported lost in mph and power while others didn't notice much. Even though the engine is the same on other models, some believe Lexus tuned it differently for the GX and hence requires Premium.
I may run a tank or two on 87 and see for myself. Since I mostly use Costo Premium the difference isn't that much, around .25-.30 cents.
Ford is the only manufacturer that I have seen publish different power ratings with regular and
premium fuels. Other than turbo/supercharged models that really must have the octane to
prevent pre-ignition "pinging" that damages the pistons, most cars that recommend premium
will run reasonably well on Mid-Grade or even Regular if your aren't pushing it. It would be nice
if one or more of the borderline OCD members here would publish any relevant charts showing
MPG results over time using various fuel grades!
Ford is the only manufacturer that I have seen publish different power ratings with regular and
premium fuels. Other than turbo/supercharged models that really must have the octane to
prevent pre-ignition "pinging" that damages the pistons, most cars that recommend premium
will run reasonably well on Mid-Grade or even Regular if your aren't pushing it. It would be nice
if one or more of the borderline OCD members here would publish any relevant charts showing
MPG results over time using various fuel grades!
Lexus does not recommend premium. Lexus requires it. My 04 4Runner V8 is recommended, but not required. GX is required.
I've read alot of posts about this. There's a long thread on the gx470 forum too. Some people reported lost in mph and power while others didn't notice much. Even though the engine is the same on other models, some believe Lexus tuned it differently for the GX and hence requires Premium.
.
Tundra 4.6 and GX 4.6 are tuned slightly different. Also, the GX is pushing around the torsen diff all day. Tundra is not. GX has a more restrictive exhaust while take away a few horses.
Historically, Toyota engines run a little different on premium vs regular. This can be seen in the 2006 SAE spec change.
Not sure if it is true anymore but at one time there were more detergents in Premium fuel. I've always tried to use Premium in the vehicles that recommended or required it as I've felt a performance penalty when lower grades were used.
IS-350 hasn't seen less than 91 Oct state side...
Previous 06 Mazda 6, 3.0 will run the ignition and cam timing up enough on 89 octane to offset the cost difference from 87 to 89 octane. That said here it is a 10 cent increase. So on a typical fill an extra $1.50 to go from 315mi to 340/345mi per tank and it simply accelerates better when it can advance the ignition and cam timing is worth it. On that engine the cost of 91/93 octane super did not pay for itself. In summer months of 100°F, it got it anyways...
That said, if the ECU is expecting a detonation free burn and you give it fuel that induces detonation, it is now relying on the knock sensors to protect your engine from damage. Those living in warm dry climates are more likely to induce damage by running low octane fuel in the summer months.
At 12.0:1 compression ratios of these engines, give them the fuel they are designed to operate on.
The higher octane is used to prevent ping or pre-detonation in high compression engines. While you can save a few dollars per tank, you can cause damage to the engine that will cost you much more to repair than you expect. Damage will be to the pistons. Modern ECU can compensate for low octane by retarding timing and increasing the amount of fuel injected into each cylinder.
Both reduce power and mpg. GX460 motor is 10.2 compression, it's considered a high compression motor.
Here is something I learned from a friend who works at a gasoline distributor. Most stations offer regular, mid-grade and premium. Many do not buy 3 grades, they buy 2, regular and premium. By Federal law retailers cannot sell gasoline with a lower than posted octane rating, but they can sell higher octane than posted. Try using Mid grade 89 octane gas. In many places you will be buying premium at a reduced price, few car manufacturers require 89 octane and few people buy it.
When I had the GX in for one of it's free CPO services, I spoke with a 'Driver' at length. The driver picks up and drops off vehicles to owners when they don't want to drive to the dealer for service work. He told me that the dealer only uses low octane on all the vehicles they put gas into. When you get that free tank of fuel, it's probably 87 octane (unless you're there watching them pump it). I've only used high octane but do wonder about testing mid grade to compare MPGs. Today at my local Shell: $2.33 reg, $2.59 Mid, $2.95 Prem.
Last edited by GX4602011; 08-30-17 at 02:26 PM.
Reason: typo
My 2 cents worth. Yes the dealer filled our new GX with regular when we picked it up. My daughter-in-law's father was a professional race driver, and spent his life owning a couple shops, and auto parts stores. I spent much of my life as a tech (mostly on airplanes) and in other technical areas, including professional pilot, etc. I have had some very interesting conversations with some very highly skilled pro's on the subject.
So the computer will compensate for the octane, that we all know. The question is does it effect performance. Or how much does it effect performance. Higher octane means essentially slower burning. Slower burning, so the fuel/air mixture doesn't explode in the cylinder. That would be bad. I have seen engines totally ruined by detonation. The computer controls that by adjusting timing, and mixture, mostly. So the prevailing view was this. If the computer has the available variances, it can give you a bit more power with slower burning fuel. That could translate to better fuel economy. I was told by a tuning expert, that most stock computers have a "Floor" to them, and will be running at that floor with low octane fuel. thus it can't adjust any lower to compensate.
My personal experience. I have a 99 GMC Seirra 3/4 ton pickup. 6.0 ltr. I kept track of every gallon of gas I put into it one yr. The year average was 15.1 mpg. That was on regular pump gas. I switched to mid grade, and for 3 months, 15.3 mpg. I tried it on our 98 Grand Cherokee, 5.2 ltr with similar results.
Yes my seat of the pants says, they run better, but I really doubt it. Now to the Lexus, it is tuned for higher octane, and I would expect to see a lot more difference.
My motorcycles, '02 Suzuki DRZ400s. Carbureted, Street version, so its a bit detuned. I can really tell the difference with premium fuel. It runs poorly on it. It just doesn't have the compression and timing to completely burn the fuel in the allowed time. However a friend has the off road model. More compression, hotter cams etc. It pings and knocks on regular. My Suzuki 650 V-Strom is fuel injected. Seems like it runs better on mid grade, but again, just my seat of the pants. However it does very slightly better on mileage on midgrade.
3.5L 2GR-FE which runs on regular is 10.8 compression.
IMO...Probably other factors at hand on GX.. I have a CX-5 that runs 13:1 (US Market) compression & on regular unleaded but it has a special 4-2-1 header.
08-26-17, 07:15 AM
