Will high octane really damage my engine?

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On Sun, 12 Jun 2005 21:15:04 +0100, jmc


wouldn't worry.
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Suddenly, without warning, TBone exclaimed (09-Jun-05 6:33 PM):

TBone, thank you for this. I may not be a mechanic but this is exact sort of explanation I was looking for - con *or* pro. I missed it originally in some of the, uh, excess posts my question has engendered, and I've still to catch up with what is below, but the wording in my manual does indeed specifically mention octane ratings. I don't have it in front of me, but seem to remember it suggested using fuel with no higher than 87 octane. 95's a bit beyond that.
For those who happen to disagree, please post an explanation as to why not, unless you have already and I just haven't made it that far down the thread.
'Course, at the moment the question's moot. The garage closed the next day, due to receiving a possibly contaminated load of fuel - just-fueled vehicles started sputtering nearly immediately after leaving the station, from what I hear.
jmc
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I wouldn't lose a minutes sleep over it. I imagine that your owners manual when talking about high octane is referring to 100+ octane racing fuel but, still I don't know why it would harm the engine. Higher octane fuel doesn't ignite as easily as lower octane fuel. With higher octane fuel you have a more controlled burn than with lower octane fuel and that is why you have detonation with low octane fuel because it so easily ignites = pre-ignition. With today's newer engines many have a higher compression ratio than they had 10 years ago. The computers on today's vehicles try to adjust for the lower octane fuel to keep them from the pinging pre-ignition. Back in the late 60's when you had such high horsepower engines coming stock in musclecars they were running 10:1 compression or higher and they had higher octane fuel at the local gas station. Now we've got the high compression ratios back in quite a few new engines and are using the computers to retard the timing so that they run on 87 octane fuel without damaging the engine from lack of octane. If the compression ratio of your engine is not high enough to require high octane fuel then you don't need it. 2 octane points above the normal premium gas here in the states will make next to no difference at all except your engine may run better and cooler and if it pinged on 87 octane fuel you will not have to worry about it pinging anymore.
Ben in TN
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no

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In my country, Chile, we only have 95 and 97 Octane gas and my 99 Dakota 3.9 L runs fine, with no engine problem! CLT.
jmc wrote:

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Where did you buy it?
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"CLT" < snipped-for-privacy@clt.cl> wrote in message news:myope.974$ snipped-for-privacy@jagger.tie.cl...
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Suddenly, without warning, TBone exclaimed (08-Jun-05 1:42 AM):

California, though.
jmc
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I was just wondering if this warning that I have read form other posters in this group was regional or covered all areas.
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"jmc" < snipped-for-privacy@NOjodiBODY.HOMEus> wrote in message
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Suddenly, without warning, TBone exclaimed (09-Jun-05 6:47 PM):

Not sure, really. I purchased it overseas, it was built in Detroit, delivered to Montana, and registered in Virginia. They did ask where my residence was, so I'm guessing it meets VA emissions standards, but then so would a vehicle built to the more rigorous CA specs, right?
Anyway, though some of it was over my head, I did enjoy the actually informative posts in answer to my question (could have done without the more numerous name-calling posts, but then that's usenet), though I'm still not sure if I should use the fuel or not. I think I'll probably just use it to top off, since gas coupons are for specific liter amounts, and thus rarely fill the tank, unless I'm willing to take a loss.
Just so I understand, if I pump high octane fuel, it burns slower, and may cause the engine to think the mixture's too lean, and make it richer, right? Which, if I understood, could cause some sort of cycle where the mixture will rapidly cycle between too lean and too rich. It's unclear to me whether this will or won't cause knock or engine problems further down the line. I also don't know what would be the symptoms of such a cycle. I would appreciate your thoughts on this.
When I buy a vehicle, I buy with the intention of keeping it 'for life', so it is important to me that I not do something now that may not show as damage until some time from now.
So, thanks again, gentlemen (for the most part) for a very educational debate. Hopefully I won't start a whole new flamewar trying to get answers to these last few questions...Oh, and what is CAFE?
jmc learning something new every day :)
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On Sun, 12 Jun 2005 21:42:04 +0100, jmc

This cycle between too rich and too lean is actually the normal realm of operation of the emission system. All the O2 sensor can tell the computer (with the exception of a VERY few select non-chrysler vehicles) is if the mixture is too rich or too lean. Can't tell it how much too rich, or how much too lean - so it says "too rich" and the computer leans the mixture untill the sensor reports "too lean". The cycle repeats itself, and the average resultant mixture is stoich.
The number of "crossings" indicates the health of the O2 sensor.

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http://www.ita.doc.gov/td/auto/cafe.html
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On Mon, 13 Jun 2005 02:29:20 GMT, "Nosey"

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snipped-for-privacy@sny.der.on.ca wrote:

If you look on your keyboard there should be a button near the "Shift" key that has "Caps Lock" written on it. Push it. ;^)
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If you can find a lower octane in the facinity, what about diluting it evey couple tank-fulls.
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It's fairly likely that the "87 octane" gas you can buy in the States and the "91 octane" gas you can buy in Germany (among other places) are, in fact, the SAME THING. Octane is measured two different ways; in the US it is specified and sold by the average of the two numbers, while in Europe it is often specified and sold by the higher number. See http://www.type2.com/archive/vintagebus/070415.html for more.
If this is what's going on where you are, the "95 octane" available at the pump is probably about equal to "89 octane" in the States. There may be a label on the pump someplace that states how the octane is measured. If not, you might get in touch with that oil company's office in your country and ask them - someone there will know which octane number they are using. The local Chrysler dealer might know, or you might try asking Chrysler national customer service in the US.

I'm not sure. However, consider this. Most gas stations in the USA sell at least 87, 89, and 91 octane. Most people don't read the manual. Some people insist on buying 91 octane for all their vehicles. If putting 89 or 91 octane in Dakotas made the engine blow up, it would have probably made the papers by now. There will be a sticker near the gas filler that says "UNLEADED FUEL ONLY"; if it was a big problem, I would think that you'd see another sticker there says "IF YOU PUT IN GAS RATED AT OVER 87 OCTANE, YOUR ENGINE WILL SURELY EXPLODE". The fact that it _is_ in the owner's manual could probably get Chrysler off the hook for a warranty claim, but it's not good business to annoy your customers that way. Now, if you went to the airport and put 100 octane av-gas in your truck, or to the race track and put 110 octane race gas in your truck, you'd probably be right to worry. IMHO.
Matt Roberds
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Suddenly, without warning, jmc exclaimed (07-Jun-05 5:29 PM):

Just a quick followup. Turns out, I shoulda paid attention to the normal octane level of UK petrol - just got back from a 6-day trip, and turns out I've been putting 95 octane in my tank every time we take a trip. Oddly, the one gas station I use locally, has low octane gas. If there's a choice of one, it's always 95 octane. So, since I've been using it on and off for a couple of years, whatever damage is already being done. After this trip, I noticed a bit of knocking. I'll put lower octane in as soon as I use some of this up.
Is there any way to mitigate any damage already done?
Oh, and this'll put things in perspective, the next time you folks in the US cringe at the gas pumps: 6 day trip. 1,100 miles or so. Something in the line of $300 worth of fuel. ARGH! Last trip we take the Dak on. Rest of the tour, it's the 1991 Toyota pickup for trips.
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"jmc" wrote:

There is no damage!!! The only danger there is, is from using less octane than required not more. I do not know how in the world people ever started thinking that higher octane will damage engine. That is bizzare!!!!
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I suggest that you contact the manufacturer for an explanation since THEY are the ones putting this warning in the owners manual.
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"SnoMan" < snipped-for-privacy@AutoForumz.com> wrote in message
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Did you see my reply? There are two ways that octane is measured, and three ways that the result of this measurement can be expressed. In the US we express it in the average of the two measurements, while continental Europe (and, I'll bet, the UK) express it as the higher of the two measurements. The odds are better than even that the "95 octane" you're buying in the UK is about the same stuff as "89 octane" in the US.
Matt Roberds
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