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89, 91 or 93 Octane

S

Stwood

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Just drove home in a 4.6 and have 150+ miles to figure out what Octane I'm going to use in the beauty. A Sunoco fan with too many options (89,91 or 93). Any thoughts (mileage, performance, engine care ...) from the experienced?
 
Stwood said:
Just drove home in a 4.6 and have 150+ miles to figure out what Octane I'm going to use in the beauty. A Sunoco fan with too many options (89,91 or 93). Any thoughts (mileage, performance, engine care ...) from the experienced?
Click to expand...

We don't have 93 in CA, you must live somewhere in the East coast. I have been running 87 for 4 months, and thought I would give it a try to 91. I have noticed the engine is smoother, throttle response is better and gas milage slightly improved. Is it a big difference? No.
If I were you I would use 87 or 89 what ever is cheaper and drive it under 4000 rpm for the first 1000 miles. Then I would change the oil to a good synthetic and 93 and then go nuts. (of course if you leased it, go nuts now, it's basically a rental.)
 
nothing but 93 here. I have noticed in other cars that lower octane and slightly reduce MPGs and a slight decrease in horse power. I wonder if Sunoco still sells the 101 octane :D
 
In general, octane and energy content are inversely proportional to a degree. The difference is small but it's a fact of the distillation process. There are so many variables however such as additives like ethanol, etc. If you can take advantage of the higher octane by increasing the cylinder pressure, then Carnot's theorem (efficiency) comes into play.
 
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What he said :)
 
I use 87 octane. (I can live with 368 hp vice the 375 hp with premium octane).

Car runs great, and gets GREAT fuel milage with 87 octane.

When I am out in Roswell, I use 86 octane. (Higher elevations need lower octane).
Again, car runs great.

I also once used 85 octane with one of my cars (not the Genesis) . Forgot where I was, but it was a higher altitude, and again, that car ran great.
 
ctrcbob said:
I use 87 octane. (I can live with 368 hp vice the 375 hp with premium octane).

Car runs great, and gets GREAT fuel milage with 87 octane.

When I am out in Roswell, I use 86 octane. (Higher elevations need lower octane).
Again, car runs great.

I also once used 85 octane with one of my cars (not the Genesis) . Forgot where I was, but it was a higher altitude, and again, that car ran great.
Click to expand...
In Denver, regular is 85 octane. Probably same in Sante Fe (higher than Denver) and maybe Albuquerque also (just a little lower).
 
Filled the 4.6 up for the first time with 87. Have driven 100+ miles on the tank and it feels fine!

Couple questions:
-It appears that the sophisticated engines theses days adjust for octane, so why do so many manufacturer's recommend higher octanes?

-Ever wonder how these gas stations do it, one truck to fill their huge underground tank and them 3 to 4 different grades at the pump?

If it is all a big scam, I've fallen for it for the last 30 years. Maybe it's the economy, but I'm going to stick with the 87 until I see/feel any problems.

Thanks for your thoughts!
 
Stwood said:
Filled the 4.6 up for the first time with 87. Have driven 100+ miles on the tank and it feels fine!

Couple questions:
-It appears that the sophisticated engines theses days adjust for octane, so why do so many manufacturer's recommend higher octanes?

-Ever wonder how these gas stations do it, one truck to fill their huge underground tank and them 3 to 4 different grades at the pump?

If it is all a big scam, I've fallen for it for the last 30 years. Maybe it's the economy, but I'm going to stick with the 87 until I see/feel any problems.

Thanks for your thoughts!
Click to expand...
Some engines will get better MPG and more HP with higher octane, which is important for advertising and CAFE regulations. Some engines actually do require premium only because of their high compression ratio. If your engine will operate with multiple octane ratings, usually the manufacturer will tell you that.

Those tankers have more than one compartment in them. Octane rating is not a scam, and is regulated and subject to testing by the government. But if you are doing business with an unscrupulous retailer, then there is some risk of not getting what you pay for.
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Stwood said:
Filled the 4.6 up for the first time with 87. Have driven 100+ miles on the tank and it feels fine!

Couple questions:
-It appears that the sophisticated engines theses days adjust for octane, so why do so many manufacturer's recommend higher octanes?

-Ever wonder how these gas stations do it, one truck to fill their huge underground tank and them 3 to 4 different grades at the pump?

If it is all a big scam, I've fallen for it for the last 30 years. Maybe it's the economy, but I'm going to stick with the 87 until I see/feel any problems.

Thanks for your thoughts!
Click to expand...

You're not going to see/feel any problems. Why? As you and everyone else knows, the car is designed to run on either regular or premium fuel. The only thing I noticed that suffered was my MPG was hurt a little bit running regular fuel. I'll take my extra 7HP at around $4 extra a tank.
 
scottdk said:
You're not going to see/feel any problems. Why? As you and everyone else knows, the car is designed to run on either regular or premium fuel. The only thing I noticed that suffered was my MPG was hurt a little bit running regular fuel. I'll take my extra 7HP at around $4 extra a tank.
Click to expand...

My fuel MPG was NOT hurt by using 87 (R+M/2) Octane. I ran 92 (91-93) for a while, and no difference. (with 87, I can live without the extra 7hp).

What does surprise me though, is that using E10 does not cause me to loose any MPG, compared to non E10. We have a place closeby that advertises Gasoline with NO Ethanol. Costs about 20 to 30 cents more a gallon. I used it for a while, and found no increse in my MPG, so I went back to E10.
In my previous car (an MKZ), using E10 got me 10 to 20% LESS MPG so I'm surprised that there is no decrease with the Genesis.
As I've stated before, the only good thing about E10 (if there is anything good about E10) is that it keeps your injectors and fuel lines clean. No need to get the costly "injection cleaning" done at various places.
 
ctrcbob said:
My fuel MPG was NOT hurt by using 87 (R+M/2) Octane. I ran 92 (91-93) for a while, and no difference. (with 87, I can live without the extra 7hp).

What does surprise me though, is that using E10 does not cause me to loose any MPG, compared to non E10. We have a place closeby that advertises Gasoline with NO Ethanol. Costs about 20 to 30 cents more a gallon. I used it for a while, and found no increse in my MPG, so I went back to E10.
In my previous car (an MKZ), using E10 got me 10 to 20% LESS MPG so I'm surprised that there is no decrease with the Genesis.
As I've stated before, the only good thing about E10 (if there is anything good about E10) is that it keeps your injectors and fuel lines clean. No need to get the costly "injection cleaning" done at various places.
Click to expand...

How does one know if they are using E10? Does Sunoco supplement with Ethanol? What gas companies use Ethanol?
 
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Stwood said:
How does one know if they are using E10? Does Sunoco supplement with Ethanol? What gas companies use Ethanol?
Click to expand...
There is usually a sticker somewhere on the pump that says the gas may contain up to 10% Ethanol.

In many major cities, ethanol use is mandated to reduce pollution. In some locations the Ethanol is mandated in the summer, and other places in the winter, depending on when the pollution is the worst. In some place the use of Ethanol is mandated all the time.

However, recent studies have shown that the production of ethanol produces more pollution than the production of gasoline. Also, ethanol is mainly produced from corn, which is used for animal feed stock in addtion to food for humans (and many food by-products). Therefore the use of ethanol in gasoline raises the price of a substantial number of food products.
 
Interesting discussion here. We've had a slightly different experience.

My parents bought a used 4.6 sedan from another member of this forum (bilmat) a week ago. Bill said that he was so accustomed to filling his automobiles with Premium fuel, that that's all the Genesis got before we took ownership.

My dad decided to experiment with some Regular grade (largely due to my suggestion due to the info in this thread).

He filled up Friday morning. There was probably a gallon of premium left in the tank. Later that afternoon he noticed the "check engine light" had illuminated (too coincidental?!). That was probably 25 miles, or about a gallon later.

I told him that new vehicles like the Genesis have so many sensors going on that it could be anything. We agreed that we might as well wait it out over the weekend at least to see if the light turns out by itself.

Sunday afternoon, on our way home from a camping trip in Watsonville, the light went off, and has yet to turn back on. Good news!


My thinking is that the engine couldn't figure out which octane it needed to automatically switch to (somewhere between the previous premium-91 and the current regular-87), but then got it together when the fuel fully mixed to an even 87.

Has anyone had a similar experience? Does mixing grades of fuel have the potential to "confuse" the sensors or cause other problems?


EDIT: I should also note that the new fuel tank also saw a switch from "expensive brand" gas (Chevron/Shell/76) to "el cheapo" gas (Rotten Robbies; probably the same as Arco and other economy brands). I'm not sure if that fact has any bearing on the check engine light or the operation of the engine.
 
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Not sure!

Have about 150 miles into my 1st 87 octane fill and notice a bit of hesitation at slow speeds/RPM's. I have a 8 cylinder and it is hesitating? Anyway, to my first post on this maybe the octane thing is not a big scam. Will try 93 next fill in a day or so and report back.

Anybody else feeling the same?
 
Stwood said:
Not sure!

Have about 150 miles into my 1st 87 octane fill and notice a bit of hesitation at slow speeds/RPM's. I have a 8 cylinder and it is hesitating? Anyway, to my first post on this maybe the octane thing is not a big scam. Will try 93 next fill in a day or so and report back.

Anybody else feeling the same?
Click to expand...
I think the hesitation is a transmission or ECU thing, and not directly related to compression ratio or horsepower that would be affected by the octane rating of the fuel you use.
 
Doesn't the 4.6 require a minimum of 87? I imagine the engine has a knock sensor and retards the timing and adjusts the electronics to compensate, but 85 might be under its threshold. Just a thought.
 
Nabber said:
Doesn't the 4.6 require a minimum of 87? I imagine the engine has a knock sensor and retards the timing and adjusts the electronics to compensate, but 85 might be under its threshold. Just a thought.
Click to expand...

Oops! My error. The regular grade gasoline used was 87 octane, not 85.

Actually, I do not believe 85 is available in California whatsoever.
 
All contemporary motors have knock sensors which retard ignition when detonation is sensed. This is done very quietly, and most of the time one cannot detect the retardation.
Detonation is usually prompted upon heavy throttle or wide open throttle. Under light cruise conditions there is materially less detonation potential.
My understanding is that 87 octane has a bit more energy than 91 octane. I have a Cadillac CTS-V (Corvette motor) which I run consistently with 87 octane, even with a 10.5 compression ratio. On highway driving comparisons I have always gotten about a 1 mpg increase using 87 octane back-to-back compared to 91 octane - testing done on flat Midwest Interstates.
Another factor to consider is that gasoline does degrade, and because of this it is best to seek out gas facilities with large volume, like Costco. In today's world 91 octane is used less and less, which can mean long-stored gasoline at some gas facilities.
 
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