True? CNN says lower octane on high octane-recommended doesn't hurt mileage.

[StageLeft]

We know that a car that recommends 91 or 93 will run optimally on that but will tolerate 87. On lower octane, power peaks are lower. I had thought that gas economy was slightly lower as well, therefore negating the small savings at the pump, but a "6 myths" article on CNN said specifically that a vehicle advising high octane that is given lower octane will lose peak power a little but its gas economy is not meaningfully affected and thus if worried about gas costs running it on 87 is fine long-term.

 

[Billb2]

Cars have knock sensors that retard the timing if knocking (preignition) occurs.
There's no more "power" in 93 octane gas than in 87 octane gas, The higher octane just allows more aggressive spark timing before knocking occurs. So as long as you're not calling for power in the range where 87 octane calls for timing changes, there's no difference between the two fuels and mileage will be the same.

 

[mooseracing]

As long as the Vehicle has a MAF, then 99.9% will have a knock sensor like stated above and will retard the timing. If you dynoed the differences you might get a couple hp/tq. On older SD, TBI, carb setups, the engien was tuned to the octane so if running a lower octane you get spark knock or detonation that you don't want. I routinely adjusted my timing daily on DD depending on teh gas I ran and how I was driving it.

 

[LTC8K6]

IIRC, there's actually more energy in the lower octane gasoline.

I seem to recall experiments on TV demonstrating this.

Edit: Nope, I was remembering another experiment.

 

[StageLeft]

Originally posted by: Billb2
Cars have knock sensors that retard the timing if knocking (preignition) occurs.
There's no more "power" in 93 octane gas than in 87 octane gas, The higher octane just allows more aggressive spark timing before knocking occurs. So as long as you're not calling for power in the range where 87 octane calls for timing changes, there's no difference between the two fuels and mileage will be the same.

So a 91-tuned engine at 87 running at, say, 70% throttle will not be stressing the octane of the 87 until we start to get up there in the throttle demand. I thought that at partial throttle less fuel/air would be used, but the existing fuel/air would still get stressed, thus a 91-tuned engine could exceed 87 without retarding the timing. If that's not the case, I will cease to use 91 and this would lead me to think it could in no way, even long term, hurt the engine.

 

[LTC8K6]

As long as you have a knock sensor, and everything is working properly, you're fine with lower octane fuel.

If you don't have the sensor, and your engine is tuned for 91, you will likely have knocking with 87, which you do not want.

 

[SoulAssassin]

I ran my 04 TL with 87 for years and no problems. I -think- it seemed a little slower off the line but it's purely speculation. If it was it certainly wasn't significant. Though the next statement that always has to be thrown into these threads is if you have enough money to afford a car that wants 91 you should have enough money to pay for it.

 

[nakedfrog]

Did they any caveats about vehicles with forced induction?

 

[vi edit]

My Passat (2.8L V6) always seemed to get about 10% better milage with premium (recommended) vs. regular. So the cost difference was a wash.

But looking back on it now, I think that was around the same time that ethanol really started being added to regular blends and any vehicle I've ever owned has taken a 10% hit in milage with ethanol. So it was probably more of a factor of that than anything.

I don't think that premium fuels were ethanol "enhanced" at that time, nor are many right now. It's the low & mid grades that are tainted with it.

 

[jtvang125]

The savings in pumping a full tank at regular over premium is only about $5-7. You can easily save that somewhere else like cutting starbucks down from twice to once a week.

 

[LTC8K6]

$5 a tankful can be a lot of money over a year.

 

[SithSolo1]

Around here it'd be $4 if I had no gas in the tank EVERY time I filled up. If I filled up once a week for a year thats $208 saved or 2.5 tanks of gas. Thats a best case scenario.

 

[caspur]

In a country with >250 million passenger cars, even if just 10% required premium (the actual # may be higher), by going on the above posters examples, $208x25 million car is more than 5 billion dollars of ADDITIONAL revenue for the oil companies. Not to mention, the profit margin for premium is greater than for regular.

 

[SithSolo1]

Originally posted by: caspur
In a country with >250 million passenger cars, even if just 10% required premium (the actual # may be higher), by going on the above posters examples, $208x25 million car is more than 5 billion dollars of ADDITIONAL revenue for the oil companies. Not to mention, the profit margin for premium is greater than for regular.

I don't think anyone would disagree with that but the discussion was over how much money an individual would spend to use the right gas in a year, not how overpaid oil companies are. Also keep in mind that revenue != profit.

 

[Nutdotnet]

Originally posted by: Skoorb
We know that a car that recommends 91 or 93 will run optimally on that but will tolerate 87. On lower octane, power peaks are lower. I had thought that gas economy was slightly lower as well, therefore negating the small savings at the pump, but a "6 myths" article on CNN said specifically that a vehicle advising high octane that is given lower octane will lose peak power a little but its gas economy is not meaningfully affected and thus if worried about gas costs running it on 87 is fine long-term.

CNN is dumb.

Yes, some vehicles can run on lower octane no problem. Even those that recommend 91+ Octane. The computer management system will simply retard timing to prevent knock.

However, and this is certainly the case more with Forced-Induction vehicles, running a lower octane, especially in the summer time, is dramatically increasing the risk of detonation, which you really, really do not want.

Running lower octane+a hot sunny day+a tromp on the gas pedal = BOOM, detonation (of course this only applies to vehicles who need higher octane, which is typical of forced-induction engines).

In addition, many of these vehicles perform better when using the octane the car is supposed to be using. I know in my R32, gas mileage and power are both decreased when running 87 vs. 91. So why bother?

 

[mwmorph]

Originally posted by: Nutdotnet

Originally posted by: Skoorb
We know that a car that recommends 91 or 93 will run optimally on that but will tolerate 87. On lower octane, power peaks are lower. I had thought that gas economy was slightly lower as well, therefore negating the small savings at the pump, but a "6 myths" article on CNN said specifically that a vehicle advising high octane that is given lower octane will lose peak power a little but its gas economy is not meaningfully affected and thus if worried about gas costs running it on 87 is fine long-term.

CNN is dumb.

Yes, some vehicles can run on lower octane no problem. Even those that recommend 91+ Octane. The computer management system will simply retard timing to prevent knock.

However, and this is certainly the case more with Forced-Induction vehicles, running a lower octane, especially in the summer time, is dramatically increasing the risk of detonation, which you really, really do not want.

Running lower octane+a hot sunny day+a tromp on the gas pedal = BOOM, detonation (of course this only applies to vehicles who need higher octane, which is typical of forced-induction engines).

In addition, many of these vehicles perform better when using the octane the car is supposed to be using. I know in my R32, gas mileage and power are both decreased when running 87 vs. 91. So why bother?

It depends on the car and has been discussed before, but as a rule of thumb, any sort of forced induction means you should definitely run the recommended grade.

As for NA engines, running 87 should present only small problems. It all depends on the engine design and particular manufacturer tune but you could either come out ahead or behind on gas mileage (I'd say overall, it's a wash but I've heard of more cars that lose mileage as compared to gaining it). Knocking on hot summer days will not occur because the ECU will know you have a tank of 87 instead of 91 or 93 and appropriately retard the timing, run richer to varying degrees and if possible, adjust cam profiles to run cooler and in some automatic transmission cars, holding lower gears because higher rpms decrease cylinder pressure. All cars are designed to run acceptably with 87, just that the premium recommended cars are designed to run better on 91 or 93.

The running rich and holding lower gears longer is usually what attributes to lower mileage but in some cars where it's on the cusp of 87 and 91, the engine tune doesn't differentiate too much from default and higher mileage can be achieved since 87, all other factors being equal, has slightly more energy content.

Thew only real issue with it is that as you run richer, the catalytic converter heats up more and it can shorten the life of your cat if done on a regular basis over a prolonged period of time and those things are a) important for emissions and b ) semi expensive, being filled with platinum and all.

 

[Apex]

Originally posted by: nakedfrog
Did they any caveats about vehicles with forced induction?

On CNN? LOL.

 

[SoulAssassin]

Originally posted by: SithSolo1

Originally posted by: caspur
In a country with >250 million passenger cars, even if just 10% required premium (the actual # may be higher), by going on the above posters examples, $208x25 million car is more than 5 billion dollars of ADDITIONAL revenue for the oil companies. Not to mention, the profit margin for premium is greater than for regular.

I don't think anyone would disagree with that but the discussion was over how much money an individual would spend to use the right gas in a year, not how overpaid oil companies are. Also keep in mind that revenue != profit.

I will disagree with that because he didn't take into account the additional refinement costs of premium vs regular. If premium costs 10 cents more per gallon and it's an additional 5 cents per gallon to refine vs regular then his number is cut in half. If it's 9 cents per gallon to refine then it's only 10%...you get the point.

 

[Zenmervolt]

Originally posted by: vi edit
My Passat (2.8L V6) always seemed to get about 10% better milage with premium (recommended) vs. regular. So the cost difference was a wash.

But looking back on it now, I think that was around the same time that ethanol really started being added to regular blends and any vehicle I've ever owned has taken a 10% hit in milage with ethanol. So it was probably more of a factor of that than anything.

I don't think that premium fuels were ethanol "enhanced" at that time, nor are many right now. It's the low & mid grades that are tainted with it.

Since Ethanol raises octane rating, I'm actually surprised it's not the other way around.

The methods used to reduce knock will reduce the efficiency with which fuel is burned. Now, on a cool day with only one person in the car and driving down a flat interstate there probably won't be a difference because the engine would be retarding timing in that scenario. Put 4 people in the car, load it with luggage, and drive it up a mountain in the middle of August and you'll notice a definite lack of power as the engine management software pulls back timing by a huge amount to prevent detonation.

Of course, when people notice the bit of extra power from higher octane, they tend to use it, which means they drive less efficiently and may not see a mileage gain.

ZV

 

[Apex]

Originally posted by: Zenmervolt

Originally posted by: vi edit
My Passat (2.8L V6) always seemed to get about 10% better milage with premium (recommended) vs. regular. So the cost difference was a wash.

But looking back on it now, I think that was around the same time that ethanol really started being added to regular blends and any vehicle I've ever owned has taken a 10% hit in milage with ethanol. So it was probably more of a factor of that than anything.

I don't think that premium fuels were ethanol "enhanced" at that time, nor are many right now. It's the low & mid grades that are tainted with it.

Since Ethanol raises octane rating, I'm actually surprised it's not the other way around.

The methods used to reduce knock will reduce the efficiency with which fuel is burned. Now, on a cool day with only one person in the car and driving down a flat interstate there probably won't be a difference because the engine would be retarding timing in that scenario. Put 4 people in the car, load it with luggage, and drive it up a mountain in the middle of August and you'll notice a definite lack of power as the engine management software pulls back timing by a huge amount to prevent detonation.

Of course, when people notice the bit of extra power from higher octane, they tend to use it, which means they drive less efficiently and may not see a mileage gain.

ZV

Ethanol has a lower BTU content than gasoline, thus the lower fuel efficiency.

 

[exdeath]

It's CNN. Question everything they tell you.

/thread

 

[Vic]

Originally posted by: nakedfrog
Did they any caveats about vehicles with forced induction?

I love the smell of a blown piston in the morning...

Run what the owners manual says to run. Anyone who takes the media's advice and does otherwise -- just to save 10 cents a gallon on gas that already costs $4 bucks a gallon -- is stupid. Sorry, but it only takes one really bad knock, and knock sensors and ECU's don't pull timing until after the fact.

 

[heymrdj]

I know my 04 Expedition with the 5.4 looses about 1.5mpg on extended use of the low octane fuel. The lack of power is noticeable to in stressful situations such as heavy launches.

 

[Scouzer]

My 2006 Pontiac Pursuit GT recommends 91 octane, but I will typically get superior mileage with plain jane 87. That being said, the car sounds noticeably crappier at the high RPM range.

It's also a tad slower, but almost imperceptibly so.

 

[Vic]

I just looked up the CNN article in question text and was interested to note that it has now been edited and a disclaimer added:
"-Editors note: This story was revised from an earlier version to clarify that the advice to use regular gas instead of premium may not apply to all cars."