Is premium fuel really needed?
12-21-17, 11:33 AM
#91
Lexus Champion
The key to these regular vs. premium discussions that go one all the time is when researching a new vehicle find out what grade of fuel is recommended/required. Then determine if you are OK with what's recommend/required BEFORE buying.
12-22-17, 04:44 AM
#92
I think you are getting fooled by a marketing tactic. Premium fuel is not cleaner or more powerful or anything "premium". It's just a variation of octane molarity. octanes are molecules that when added to fuel, reduce the fuel's volatility. That's why there are numbers 87, 89, 91.. This is not the exact molar solubility but it's a easy to understand range. It's just a means of measure we created, like PH of acids and bases... PH is not a scientific number of anything.
ANYWAYS, what I'm saying is if your car does not recommend or require premium, you are doing it no favors by putting premium in it. The car has restraints on how far it can advance and if it was not engineered around premium, it will not be able to advance enough for it. And that's the only thing "premium" fuel is doing. Again, it is not cleaner or "better" in any other way.
ANYWAYS, what I'm saying is if your car does not recommend or require premium, you are doing it no favors by putting premium in it. The car has restraints on how far it can advance and if it was not engineered around premium, it will not be able to advance enough for it. And that's the only thing "premium" fuel is doing. Again, it is not cleaner or "better" in any other way.
12-22-17, 07:48 AM
#94
Bit of history regarding gasoline additives, premium (high-test, ethyl) used to have
various detergents in addition to the Lead to boost Octane. When you had a rough
running car you could fill 'er up with Sunoco 260 and the additives might dissolve
some of the crud out of the Carburetor (look it up if you're under 25!). That and
gunning it around in low gears/high RPM comprised a "2nd gear Tune-Up".
Now that nearly all fuels are "Top Tier" and have loads of additives it would not
seem to be benefit to spend for a slower burning fuel that the engine can not
utilize fully.
various detergents in addition to the Lead to boost Octane. When you had a rough
running car you could fill 'er up with Sunoco 260 and the additives might dissolve
some of the crud out of the Carburetor (look it up if you're under 25!). That and
gunning it around in low gears/high RPM comprised a "2nd gear Tune-Up".
Now that nearly all fuels are "Top Tier" and have loads of additives it would not
seem to be benefit to spend for a slower burning fuel that the engine can not
utilize fully.
12-22-17, 08:05 AM
#95
Driver School Candidate
That AAA study shines light on "recommended" not required. So this does not really help our case much. The NX runs a turbocharged 2.0L inline 4 cylinder. This spells out high compression and high heat. Heat causes knock, the fuel spontaneously ignites. The RX hybrid is a naturally aspirated 3.5L V6. This spells out mild compression, Less heat would be created from the compression stroke on this engine.
I use premium during the summer but mid-grade during the winter. With outside temps around 30F, I don't see the internal cylinder temp raising the air fuel mixture high enough to knock. But to each their own. I can tell you that Lexus wants premium in the tank. Pg 392 of the NX manual states that if a octane of less than 91 is used it can result in engine damage and a voided warranty. Lexus also states that if only low octane fuel is available that the vehicle should not see heavy loads until refueled with higher octane.
I use premium during the summer but mid-grade during the winter. With outside temps around 30F, I don't see the internal cylinder temp raising the air fuel mixture high enough to knock. But to each their own. I can tell you that Lexus wants premium in the tank. Pg 392 of the NX manual states that if a octane of less than 91 is used it can result in engine damage and a voided warranty. Lexus also states that if only low octane fuel is available that the vehicle should not see heavy loads until refueled with higher octane.
I tried a couple of fill ups without premium and the gas mileage was about the same, without any extra engine noise. I might test it more, but I am just using premium for now.
12-22-17, 08:20 AM
#96
Lexus Champion
Little or no knowledge is quite dangerous. Knowledge plus real life experience gained is real true knowledge. Guy like me nearling age of 80, done it, seen it so much during my life time.
Running on cruising speed on wide open high way will make the engine hot and helps get rid of internal build up. That happens when I drive out to our cabin in the foothills.
Running on cruising speed on wide open high way will make the engine hot and helps get rid of internal build up. That happens when I drive out to our cabin in the foothills.
03-02-19, 07:37 AM
#97
89 Winter 91+ Summer
In Michigan in our 2016 NX200t I find it works well to use 89 in Winter and 91+ in Summer. Often the higher octane gas will have more ethanol in it, so I tend to use the lowest octane that makes it run smooth. Ethanol gives worse mileage based on energy content.
03-02-19, 02:15 PM
#98
I love the revival of an old thread. I really do, that is not sarcasm. Anyways,
Ethanol... That's a whole new can of worms. If you were able to accurately log that the small (1-5%) differences in ethanol content changed the performance of your vehicle, I would be impressed. There are far too many variables at play, Your DD is not in a controlled environment. You may see 22mpg on one tank and 24mpg on another. This doesn't mean ethanol content did it. Between octane stability, flame speed and BTUs of energy, Ethanol is nominally different in small percentages like that. It has its pros and cons but the oil companies did a damn good job at only showing its cons over the years.
The Hybrid has a VVT actuated Atkinson cycle so it is not running 12.5:1 compression. That is just what the numbers come out to when bore/stroke is measured.
Ethanol... That's a whole new can of worms. If you were able to accurately log that the small (1-5%) differences in ethanol content changed the performance of your vehicle, I would be impressed. There are far too many variables at play, Your DD is not in a controlled environment. You may see 22mpg on one tank and 24mpg on another. This doesn't mean ethanol content did it. Between octane stability, flame speed and BTUs of energy, Ethanol is nominally different in small percentages like that. It has its pros and cons but the oil companies did a damn good job at only showing its cons over the years.
The Hybrid has a VVT actuated Atkinson cycle so it is not running 12.5:1 compression. That is just what the numbers come out to when bore/stroke is measured.
03-02-19, 06:39 PM
#99
My point mainly was that there is no point in paying for more octane than the engine needs. In the NX turbo this seems to be between 89 and 91. Especially because adding more ethanol is an easy way to increase octane - gas company’s likely take this approach. Then you’re paying more for unnecessary octane and actually a little less energy.
Above 89 in winter or 91 in summer also makes no difference to the NX fuel economy in my experience.
Above 89 in winter or 91 in summer also makes no difference to the NX fuel economy in my experience.
03-03-19, 05:38 AM
#100
Intermediate
My point mainly was that there is no point in paying for more octane than the engine needs. In the NX turbo this seems to be between 89 and 91. Especially because adding more ethanol is an easy way to increase octane - gas company’s likely take this approach. Then you’re paying more for unnecessary octane and actually a little less energy.
Above 89 in winter or 91 in summer also makes no difference to the NX fuel economy in my experience.
Above 89 in winter or 91 in summer also makes no difference to the NX fuel economy in my experience.
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GlenK (03-04-19)
03-03-19, 05:59 AM
#101
More specifically, Lexus recommends 91 for the NX turbo. See below.
https://lexus2.custhelp.com/app/answ...xus-vehicle%3F
https://lexus2.custhelp.com/app/answ...xus-vehicle%3F
03-03-19, 09:23 AM
#102
Intermediate
If you noticed, the website indicated 91 as “recommended minimum”. Car manual states “Premium unleaded gasoline only”. What Lexus is saying is that engine will tolerate 91. That means, engine timing will retard to offset possible spontaneous ignition, causing knocking and the rest of issues… However, premium gas offers the best engine performance and assures that engine stays out of troubles (so to speak).
In US, 91 is mid-grade gas. I am too “cheap” and plan on keeping NX for a little while, so I am not willing to take a risk over couple of hundred bucks per year difference between 91 and 93. Consider it is piece of mind, if you will.
In US, 91 is mid-grade gas. I am too “cheap” and plan on keeping NX for a little while, so I am not willing to take a risk over couple of hundred bucks per year difference between 91 and 93. Consider it is piece of mind, if you will.
03-03-19, 01:42 PM
#103
Here in Montreal, Canada, grades are normally 87, 89 and 91. Sometimes we see 94 at Petro-Canada stations. Own my ‘18 NX since a year and always use 91 without issue, dealer says there is no need to go for 94. I get my premium gas at Costco where gas is 10-12 cents/liter (~ 45 cents/gallon) cheaper than major brands. Fuelled up today at Costco for 1,26$/liter for premium while it was 1,40$/liter at other stations
03-03-19, 01:51 PM
#104
From the Lexus website:
“Use of unleaded gasoline with an octane rating lower than what is listed for your model year vehicle may result in engine knocking.”
I think we are just fine with 91.
“Use of unleaded gasoline with an octane rating lower than what is listed for your model year vehicle may result in engine knocking.”
I think we are just fine with 91.
03-03-19, 03:11 PM
#105
Intermediate
Here in Montreal, Canada, grades are normally 87, 89 and 91. Sometimes we see 94 at Petro-Canada stations. Own my ‘18 NX since a year and always use 91 without issue, dealer says there is no need to go for 94. I get my premium gas at Costco where gas is 10-12 cents/liter (~ 45 cents/gallon) cheaper than major brands. Fuelled up today at Costco for 1,26$/liter for premium while it was 1,40$/liter at other stations