Higher Octane...bad?

[MadisonMPG]

With my on going crusade over at Dodge Forum someone just posted this.

Originally Posted by CSCustomCars

Octane is the fuels resistance to knock. Using higher octane than what the engine is designed for can actually shorten the life of the motor.
Always use the recommended octane that the engine was designed for.

Is there any validity to this? I've always thought engines just advanced timing to meet whatever octane there was... (new engines, I know old engines don't)

[SentraSE-R]

AFAIK, modern ECUs retard timing to prevent engine damage with lower octane fuel. I don't know why they should advance timing in anticipation of higher octane fuel. I'd have stated it differently:

Octane is the fuels resistance to knock. Using higher octane than what the engine is designed for can actually shorten the life of your wallet.
Always use the recommended octane that the engine was designed for.

[gone-ot]

...yes, the "new" engine-management computers actually *WILL* advance the timing to "take advantage" of higher octane (less knock-prone) gasoline.

...that's *part* of the reason why some of the "newer" cars can often achieve better FE when using E85-fuel, which has 105 octane rating, due to ethanol's much higher octane rating (113) than 'straight' gasoline.



...so, the real answer may lie in what year vehicle the guy was talking about--pre-electronics carburation, OBDI or todays' OBDII?

[thatguitarguy]

It doesn't make sense to spend more money on higher octame fuel if your engine is not knocking, and definitely not if the manufacturer calls for lower octane.

"Higher octane" does not mean "higher quality", as some people seem to think.

Here in Colorado there is ethanol in all grades of fuel. Don't know for sure, but I'm guessing that they just put more ethanol in the higher octane fuels and charge a lot more for the effort, while they put mostly ethanol in E-85 and charge a lot less for it. Go figure.

If I had engine knock I would buy mostly low octane and mix in a little E-85 to find the right mix and save some money, but at this altitude the burn is slowed naturally by much thinner air, so there isn't much need for higher octane fuels. Sure doesn't stop people from buying it though.

[MadisonMPG]

Originally Posted by Old Tele man

...so, the real answer may lie in what year vehicle the guy was talking about--pre-electronics carburation, OBDI or todays' OBDII?

We're talking about OBDII.

This is pretty much the conversation we have been having about it. (the last 2-3 posts)

Originally Posted by CSCustomCars

NY uses 10% ethanol in winter, and then switches back to summer blend with I believe is less than 5% ethanol. It may be 100% gasoline.
I think they just switched over too, cause my Silverado was getting 15 mpg's all winter, but it's back up to 17 now.

Originally Posted by Cas161

I do get a little better milage with 93 octane (2-3 mpg), but is it worth spending the extra $$$ on a regular basis? Is higher octane better for the motor?

Originally Posted by MadisonDakota

No, unless it is pinging on lower octane. Lower octane fuel is just as good if the timing doesn't change.

Now having said that, E10 is not good, it is/was pushed along side "global warming" to make the Earth happy. You say 2-3mpg boost in mpg? 10% of 20mpg is 2mpg. That's the amount of ethanol in your gas. New engines usually pull timing (retard) in order to run 87 with E10. Theoretically, it should run the same timing as 100% gas, but it doesn't. Less timing=less power.

If your Premium is more than eh 15% more expensive, don't buy it. If it is less than say 10% more, buy it. If it is in the middle, you be the judge. That is assuming your Premium is 100% gas, if it is E10, buy 87. If the mid grade gas doesn't contain ethanol, and the other two do, buy the mid.

Cliffnotes:
Always buy 87 if it is 100% gasoline. Buy 87 E10 if both 87 and Premium contain ethanol. Buy Premium when it is <12% more than 87 (assuming the 87 is E10 and the Premium is 100%)

Baby cliffnotes:
Avoid ethanol. If you have no choice, buy E10 87/Regular.

Does everybody get it?

[rmay635703]

Originally Posted by thatguitarguy

It doesn't make sense to spend more money on higher octame fuel if your engine is not knocking, and definitely not if the manufacturer calls for lower octane.

Um, generally fully functional OBDII cars cannot knock (at least not detectably to the driver)

If you have a timing guage and tap on an OBDII motor with a ballpean hammer lightly the timing retards rapidly.

So higher octane "May" improve some factor of performance, my Buick for example running hi test in the winter has its FE restored to summertime levels but the effect doesn't pass into the summer sadly. Also the additional cost exceeds the gain most of the time.

But I can't say hi octane is not beneficial in some circumstances, Ever try to run an older Smartcar on 87 octane ethanol? It is well rather craptaskic.

Also my Dodge gets BETTER FE running 100+ octane e85 mixed 50/50 with 89 octane e10 in the winter (again effect does not seem to translate into warmer weather)

Cheers
Ryan

[MadisonMPG]

Originally Posted by thatguitarguy

It doesn't make sense to spend more money on higher octame fuel if your engine is not knocking, and definitely not if the manufacturer calls for lower octane.

I am not advocating using higher octane. I am asking: Does using higher then approved octane (Premium) shorten the life of an OBDII engine meant to run on 87 (Regular)?

[gone-ot]

Originally Posted by MadisonMPG

I am not advocating using higher octane. I am asking: Does using higher then approved octane (Premium) shorten the life of an OBDII engine meant to run on 87 (Regular)?

...two letter answer: no.

...octane is a "knock-limiting" value and basically nothing else! So, using 91 octane ("Premium") in a car designed for 87 octane ("regular") will NOT damage it whatsoever.

...what can damage an engine, however, is using different fuels containing god-knows-what-kind of additives that don't burn cleanly.

...this has NOTHING to due with octane--but is, too often, one (of many) false claims made for the additives--but rather the "left-over deposits" from faulty combustion, which CAN by themselves cause "glowing carbon" deposits which CAN result in pre-ignition and cause damage (if the computer can't yank the timing back quick enough).

...read the WIKI explanation for octane, it should help you come to your own answer.

[MadisonMPG]

Originally Posted by rmay635703

.

Also my Dodge gets BETTER FE running 100+ octane e85 mixed 50/50 with 89 octane e10 in the winter (again effect does not seem to translate into warmer weather)

Is it E10 89 or 100% gas 89?

[rmay635703]

Originally Posted by MadisonMPG

Is it E10 89 or 100% gas 89?

87/89 octane is all e10 around here, a couple stations carry 100% gas on their 93 octane.

I buy both grades out of the same pump at Renew energies stations that sell e10/20/85.

Cheers
Ryan