Regular gas VS Premium myths

Interesting artical on cartalk about the myths between the two types.


http://www.cartalk.com/content/features/premium/myths.html

Premium gas gives you more miles per gallon than regular gas. is not always a myth. Honda recommends that you use premium gas when towing over 3,500 lb. I have tried it and get about 2-3 mpg better mileage towing with premium. With regular gas and a heavy load, the ignition timing is sometimes retarded into the single digit range by the knock sensors, which accounts for the difference.
Premium vs. regular when not towing? No noticable difference.

Towing or loaded or high speed long drive use middle or premium,slow drive to work use reg.

My other vehicle is an older Seville. It gets used rarely and mostly as a short trip grocery getter. It has been prone to carbon buildup resulting in once a year top engine cleanings. My Cadillac dealership mechanic, I always specify the same guy, suggested I stop using the recommended premium gas. This, supposedly, would reduce the amount of carbon build up resulting from my driving habits.

Any thoughts on his suggestion? I'm still using premium, because I'm reluctant to change over.

My Regal GS states to use premium all of the time. It's supercharged. If I put in regular, you can tell the difference.

The typical difference between grades of fuel is the octane rating. The higher the octane rating, the higher the volatility of the fuel. Since I live at 5000 feet above sea level, regular (85 octane) gasoline is plenty volatile at that altitude and spending the extra money for premium (90+ octane) is simply wasting money. If you live at sea level, you may see a difference in how your vehicle responds with different octane grades as the higher octane rating will correlate to increases in volatility of the fuel.
As for additives, most refineries include the same detergents and additives in their top two grades of gasoline (87 and 90+ octane). Low grade and you are on your own.

The typical difference between grades of fuel is the octane rating. The higher the octane rating, the higher the volatility of the fuel.

Just for the record... the opposite is true. The higher the octane rating the less volatile the fuel is. The octane rating measures the fuels ability to resist detonation.

Regular unleaded fuel has a higher volatility and more BTUs per gallon.

When discussing diesel fuel we deal with cetane ratings instead of octane.

Just a follow up to my previous message.

Gasoline is very complex. There are many ways to raise octane ratings. One of the more common methods today is to add ethanol. So we take regular gasoline with about 110,000 BTUs in a gallon and add 10% ethanol with only about 84,000 BTUs per gallon to raise the octane rating a few points and make people think they're getting more power.

You could actually make high octane rating fuel that has more BTUs per gallon than regular, but that would cost more money. Oil companies go to great lengths to keep their additive packages secret (they all use the same base gasoline) so we don't know what each brand uses. You can bet they do it the cheapest way possible (ethanol).

From the chemist point of view... Gasoline does not have "octane" (C8H18) in it... It more of a blend of an isomer of octane (2,2,4-trimethylpentane) and heptane (C7H16) ... The octane name and # is related to the percentage # of isomer of octane to the amount of heptane and how well the engine resists knock as compared to tests using pure octane (rated as being 100).

From the chemist point of view... Gasoline does not have "octane" (C8H18) in it... It more of a blend of an isomer of octane (2,2,4-trimethylpentane) and heptane (C7H16) ... The octane name and # is related to the percentage # of isomer of octane to the amount of heptane and how well the engine resists knock as compared to tests using pure octane (rated as being 100).


I'm a little confused about what you posted but it sounds interesting. I remember leaded fuels with an octane rating of over 100. How can you have a fuel that has an octane rating of over 100 if pure octane is rated 100?

ChrisM,

The easiest way to answer your question is to remember that octane "rating", and "octane" are two different things. Do a google search and put in "octane ratine", then click on the Wikipedia line.

Hennie

I'm a little confused about what you posted but it sounds interesting. I remember leaded fuels with an octane rating of over 100. How can you have a fuel that has an octane rating of over 100 if pure octane is rated 100?

Yes, leaded fuels do have octane ratings over 100 but there is a catch to this... Here is where it becomes crazy... Most people equate over 100 octane rating as being aviation fuel or "AvGas"...(for use in piston aircraft engines)... (and then there is jet fuel which for commercial planes is pure kerosene and for the armed forces is a kerosene gasoline blend, which produces less "black smoke trails".)

Your typical Aviation fuel or AvGas, which has an octane rating of 100 here on land but when used in higher elevations (less atmospheric pressure, decreased temperature), will work at an octane rating over 100…. With me so far? Now here on land there is AvGas that can have a higher then 100 octane rating… Another common organic compound added to “fuel” are aromatics. Benzene and toluene, (a methyl, CH3, substituted benzene ring), have octane ratings of 115 and 103.5 respectively. AvGas typically in the industry uses toluene but depending on the manufacturer of the AvGas and/or Jet Fuel for commercial use, is allowed up to 25% of added aromatics.
The blend of toluene with the other gasoline hydrocarbons give those 101 to 103 octane rated gasoline blends. The best of the best aviation fuels have an octane working rating of 130…

A manufacture will void a warranty if they can prove the engine damage came from using lower octane than "required". Some do say "recommended" which it's up to you. Granted most modern cars knock sensors will keep the engine from getting damaged but are you willing to chance it. I could always tell which Acuras had been run on the cheap gas their whole life. They would not have the same feel as a car that used premium.

As a previous salesman of Acuras for a long time I had one thing to say to people who complain about using premium. "Maybe you're not ready for a Acura let me show you a Honda." This may sould like I'm being a jerk but if you're going to by a nice car treat it that way and stop being so cheap. These cars that require the premium are designed around it and you will get less mpg, hp and less life. For those who say mine has run fine on the cheap stuff, all I can say is you're lucky probably because you drive a honda.

Would you put the cheap stuff in a NSX or a 575 Maranello?!?!?

Run what the folks that built the motor tell you too. If it's regular then go with reg, and don't think you'll "gain" anything by adding a tank of hi-test whenever someone else is paying for the fill. If the folks who built it say run ELF race fuel that's so nasty you have to drain it between events then run the ELF.

My Regal GS states to use premium all of the time. It's supercharged. If I put in regular, you can tell the difference.

If you use regular in a forced induction engine you are asking for trouble. The supercharger increases your compression ratio thus causing a need for higher octane. If you use regular your ecu has to pull timing to stop ping. If you have a SC I would recommend the highest octane you can find.

My other vehicle is an older Seville. It gets used rarely and mostly as a short trip grocery getter. It has been prone to carbon buildup resulting in once a year top engine cleanings. My Cadillac dealership mechanic, I always specify the same guy, suggested I stop using the recommended premium gas. This, supposedly, would reduce the amount of carbon build up resulting from my driving habits.

Any thoughts on his suggestion? I'm still using premium, because I'm reluctant to change over.

What reason/evidence were you given for the need of a "top end cleaning"? Where you experiencing Pinging? What type of fuel does the manual suggest? I don't think fuel is an issue. Both premium and regular have additives to help keep combustion chambers clean. I think it is more driving habits. Try running a fuel injector cleaner every third tank, and take it out on the highway for a little trip once in a while.

Thanks for your input on this, George.
What reason/evidence were you given for the need of a "top end cleaning"? Where you experiencing Pinging?
I'm no mechanic. Not "pinging", it's hard to describe. It was as if the pistons encountered some type of restriction at the top of the stroke. Mechanic said he was surprised I didn't damage the Wrist Pins. Whatever he does, make the problem go away and the engine runs much smoother.


What type of fuel does the manual suggest? I don't think fuel is an issue. Both premium and regular have additives to help keep combustion chambers clean.
Calls for premium and I've always used 91 octane or better.

I think it is more driving habits. Try running a fuel injector cleaner every third tank, and take it out on the highway for a little trip once in a while.
That's what the mechanic says. I need to run it once in a while. Honestly, I've had two sets of Michilens (sp) dry rot.

What reason/evidence were you given for the need of a "top end cleaning"? Where you experiencing Pinging? What type of fuel does the manual suggest? I don't think fuel is an issue. Both premium and regular have additives to help keep combustion chambers clean. I think it is more driving habits. Try running a fuel injector cleaner every third tank, and take it out on the highway for a little trip once in a while.

Are you having pre ignition problems? Does the motor try to keep running after the key is turned off? If so, you have carbon build up in the top of the compression chamber. Before fuel injection, we would pour a little water throught the carbarator with the motor running and it would knock out the carbon. Have no idea how to address fuel injection!:confused:

Are you having pre ignition problems? Does the motor try to keep running after the key is turned off? If so, you have carbon build up in the top of the compression chamber. Before fuel injection, we would pour a little water throught the carbarator with the motor running and it would knock out the carbon. Have no idea how to address fuel injection!:confused:
Nope, nothing like that "25".

The mechanic says there is very little clearance at the top of the stoke on Cadillac's Northstar engines. The carbon would build up to a point where the pistons would encounter interference. The cleaning was a two step process, requiring an overnight stay at the dealership. The second step was for a piston ring cleaning that needed the overnight soak.

Are you having pre ignition problems? Does the motor try to keep running after the key is turned off? If so, you have carbon build up in the top of the compression chamber. Before fuel injection, we would pour a little water throught the carbarator with the motor running and it would knock out the carbon. Have no idea how to address fuel injection!:confused:

You can do the same with fuel injection. Just find a vacuum line and use it to draw small amounts of water into the intake from a water bottle. Key is small amounts, you don't want to hydro lock your engine. We use this method in my Miata club, on some of out higher performance cars.

Pizza Man,
Bring the caddy down here and we will "let her eat" as the locals say. :Dhttp://images.kodakgallery.com/photos2411/4/12/47/34/89/3/389344712405_0_ALB.jpg

Yes, leaded fuels do have octane ratings over 100 but there is a catch to this... Here is where it becomes crazy... Most people equate over 100 octane rating as being aviation fuel or "AvGas"...(for use in piston aircraft engines)... (and then there is jet fuel which for commercial planes is pure kerosene and for the armed forces is a kerosene gasoline blend, which produces less "black smoke trails".)

Your typical Aviation fuel or AvGas, which has an octane rating of 100 here on land but when used in higher elevations (less atmospheric pressure, decreased temperature), will work at an octane rating over 100…. With me so far? Now here on land there is AvGas that can have a higher then 100 octane rating… Another common organic compound added to “fuel” are aromatics. Benzene and toluene, (a methyl, CH3, substituted benzene ring), have octane ratings of 115 and 103.5 respectively. AvGas typically in the industry uses toluene but depending on the manufacturer of the AvGas and/or Jet Fuel for commercial use, is allowed up to 25% of added aromatics.
The blend of toluene with the other gasoline hydrocarbons give those 101 to 103 octane rated gasoline blends. The best of the best aviation fuels have an octane working rating of 130…

Nicely written. For those who's eyes just glazed over reading this, an easy explaination is that octane rating uses the chemical octane as the reference point and assigned it a rating of 100. All other fuels have an octane rating that is based on a comparision to the chemical octane.

The mechanic says there is very little clearance at the top of the stoke on Cadillac's Northstar engines. The carbon would build up to a point where the pistons would encounter interference. The cleaning was a two step process, requiring an overnight stay at the dealership. The second step was for a piston ring cleaning that needed the overnight soak.

Excuses excuses... It's really your fault... It's more then just driving it once and awhile or driving it once and awhile at highway speeds... It's about putting the petal to the metal, every once in a while to clean out the injectors and blow out the carbon build up. It's time to take out the caddy and challenge fellow RL owners to a drag race... Or you can simply get on the onramp of your favorite highway and open it up... Now I am not the type to condone fast starts and pushing a vehicle past the speed limit, but really the engine requires it every once in a while to remain "healthy". As great as the Northstar engine technology is, the ceramic component is more prone to stuck on carbon buildup. All fun aside there is 4 caddies with the northstar V8 in my immediate family and all have had this issue and all have been fixed by making the engine have to work.

I also will make the RL work hard and will open it up to help clean things out... You will be shocked how more the RL will be in response after some high rev runs...

In order to accomplish that xman. I'd have to get behind the wheel of the Caddy. Since the RL, maybe I've been behind the wheel 4 times in 16 months. :( Honestly, a tank of gas lasts over a month!

In order to accomplish that xman. I'd have to get behind the wheel of the Caddy. Since the RL, maybe I've been behind the wheel 4 times in 16 months. :( Honestly, a tank of gas lasts over a month!

Wow... That's a tuff one... You could always get rid of it and get your wife her own RL... At least you could tell her that.. Just think 2 RL's....:D

Wow... That's a tuff one... You could always get rid of it and get your wife her own RL... At least you could tell her that.. Just think 2 RL's....:D
I agree with you, I'm the problem causing the carbon issue. I guess I need to be more diligent and get in it and jump on it every now and again. If I take it to work that accomplishes nothing. I work 1 1/2 miles from home and that leaves the wife stranded at home because she won't drive the RL. She doesn't work.

What do you think of the mechanics suggestion of using lower octane fuel to combat the carbon issue?

I should probably get rid of the Caddy and get her something that revs a little higher.

I appreciate everyone's input on this.

What do you think of the mechanics suggestion of using lower octane fuel to combat the carbon issue?

The only reason I can think of that lower octane fuel would achieve anything is that it might cause detonation (pinging), which would blow the carbon off. I'm not sure the ignition management system would allow that, but if it did its not a good thing. Lower octane fuel contains just as much carbon as the higher stuff.
Let one of your teenage relatives take it on a date once and a while. Problem solved. :D

Let one of your teenage relatives take it on a date once and a while. Problem solved. :D
Thanks, Webbie. I love it! :D

I agree with you, I'm the problem causing the carbon issue. I guess I need to be more diligent and get in it and jump on it every now and again. If I take it to work that accomplishes nothing. I work 1 1/2 miles from home and that leaves the wife stranded at home because she won't drive the RL. She doesn't work.

What do you think of the mechanics suggestion of using lower octane fuel to combat the carbon issue?

I should probably get rid of the Caddy and get her something that revs a little higher.

I appreciate everyone's input on this.

The motor has a higher compression ratio and requires the higher octane. You run the risk of a misfire using lower octane... Hence you could damage a cylinder. What people don't realize is that in a gasoline driven engine the compression of the air/fuel mixture causes an increase in temperature. Higher compression ratio engines cause more pressure and thus higher temperatures. The problem with higher temperatures in a compression chamber is that the gasoline has the potential to combust with out the need of the sparkplug. Higher octane gasoline is less prone to premature detonation. If you get a premature misfire during one of the engine strokes it can result in some major damage....

Getting a replacement vehicle that runs a little higher in revs just means you have an engine that has to run at higher revs to keep the vehicle moving. (This is due to the vehicle’s gear ratio and/or engine output to weight ratio).

One other solution to help is using gasoline that has the most techron additive. Techron is a "detergent" that helps keep the engine "clean" form carbon buildup. You may or may not like the company, but Shell has the most technron and in my experience and opinion works best in the caddy engine.

My Austin Healeys wouldn't run right if you didn't perform "the Italian tuneup" every once in at least 1000 miles. The manufacturer recommended pulling the head and having it "de-coked" every 15k miles due to carbon buildup. :eek:

I never had to perfom this "de-coking" process because I had to keep my foot into it to keep up with traffic. The last one I had only had a 1275 cc motor. That is only 79 cubic inches. :eek:

One other solution to help is using gasoline that has the most techron additive. Techron is a "detergent" that helps keep the engine "clean" form carbon buildup. You may or may not like the company, but Shell has the most technron and in my experience and opinion works best in the caddy engine.
I'm using Texaco, which also uses the Techron additive, in my Ridge. There are only a few Shell stations nearby. I've never considered using Texaco in the Caddy, but I will now.

Thanks, xman.

I'm using Texaco, which also uses the Techron additive, in my Ridge. There are only a few Shell stations nearby. I've never considered using Texaco in the Caddy, but I will now.

Thanks, xman.

When you go for the fill up and take it home, floor it for about 6 seconds... Start at a speed around 10mph... 6 seconds should bring you to about 65mph.

When you go for the fill up and take it home, floor it for about 6 seconds... Start at a speed around 10mph... 6 seconds should bring you to about 65mph.
Will I need to wear a neck brace? :eek: :D

Will I need to wear a neck brace? :eek: :D

No... Just put your head back against the headrest. No cheating.... Press the accelerator all the way down to the floor... Another suggestion...don't bring the misses with you. :eek:

ChrisM wrote:I never had to perfom this "de-coking" process because I had to keep my foot into it to keep up with traffic. The last one I had only had a 1275 cc motor. That is only 79 cubic inches.
That brings back fond memories. I used to race a MG Midget with a 1275 bored 0.040" over to 1314 cc. With racing modifications, it produced about 125 HP, turned 8,000 RPM in fourth gear and could do 125 MPH. Not bad for an engine design that harkened back to the early fifties, was undersquare, and had only two intake and three exhaust ports. I never had to de-coke mine either. :D

all of this talk about carbon build up reminds me of when I started driving. My mother drive like a grandma so when I drove I cleaned everything out. The car ran better and got better mpg. My mother would get in and say the car felt more peppy. She was happy until I wasted her clutch. I got the I drove a car for 125K and never needed a new clutch. LOL

10 years ago when I got my Infiniti, they recommended high octane. I settled for the mid grade. I bought gas at a discount station because I liked their coffee.

Every few months I had to clean the intake assembly, where the butterfly valve is. I attributed it to lower octane than what was recommended.

Several years ago a friend suggested Shell gas. It was only a penny a gallon more expensive.

Well, I went a full year before I cleaned the intake assembly. Car ran smoother.

Shell is the only fuel I purchase.

all of this talk about carbon build up reminds me of when I started driving. My mother drive like a grandma so when I drove I cleaned everything out. The car ran better and got better mpg. My mother would get in and say the car felt more peppy. She was happy until I wasted her clutch. I got the I drove a car for 125K and never needed a new clutch. LOL

My Mother always knew when I had "cleaned the carbon out of her engine", she claimed afterwards she would accidently "light 'em up" at stop signs.

It was a 76 Olds Cutless with a 350 engine, 4 barrel carb. Never found out how fast it would go cause it would shake so bad when it hit 90.