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
'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.
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
Ben in TN
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?
learning something new every day :)
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.
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.
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.
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
Posted using the http://www.autoforumz.com interface, at author's request
Articles individually checked for conformance to usenet standards
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.
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