Mixing different grades of gas (87, 89, 93)?
RBStern
>Is it OK? I have an I/O V8 Mercruiser 305, 1984.
Someone I know in the gasonline distribution business explained to me that the
difference in octane is acheived by the amount of an octane additive added to
the base gasonline. Add equal amounts of 87 and 89 octane and you've got 88
octane. Mixing is not an issue, unless your engine has minimum octane
requirements.
Rich Stern
Karl Denninger
Well, not quite. Mixing 87 and 89 in equal quantities may not give you 88.
You can, however, use this if you have only 87 and 92, for example,
available to you and your boat requires 89. If you mixed roughly 50/50
in that situation you'd have gas that would almost certainly exceed the 89
requirement (which is all that's important).
Being a point or two over won't hurt your engine (but it may not run "right").
Being a couple of points under can, under the wrong load conditions (ie:
heavy load "aka" typical marine use) cause severe enough detonation to do
severe damage (like burn holes in pistons) to your engine.
--
--
Karl Denninger (ka...@denninger.net) Web: childrens-justice.org
Tired of the broken divorce system in the United States and what it's doing
to our kids? SIGN the online petition for equal parental - and children's -
rights at the above URL. Make a difference in a kid's life today.
Real-time chat now available from the above web page
RBStern
OK. Can you offer an explanation?
>You can, however, use this if you have only 87 and 92, for example,
>available to you and your boat requires 89. If you mixed roughly 50/50
>in that situation you'd have gas that would almost certainly exceed the 89
Again, please explain. You are implying that the ratio is not an average of
the two component values. The only difference in your example from mine that I
can detect is that you imply that a .5 octane ratio increment is a good enough
safety margin. That doesn't clarify why you are rejecting the math I offered.
I said (87 + 89) / 2 = 88. You said "maybe false."
You said (87 + 92) / 2 > 89 with a safety margin for engines that require 89.
I agree.
But that strikes me as nit picking.
My understanding is that Octane rating represents the ratio of iso-octane to
heptane as an anti-knock additive in gasonline (as well as some other liquid
fuels). If you create a 50/50 mixture of two different octane ratings, mix
them together, the result is an additive ratio that is exactly the average of
the two additive ratios of the components.
Please, if you have a clear explanation for why I am in error, say so.
Rich Stern
Karl Denninger
RBStern <rbs...@aol.com> wrote:
>> Mixing 87 and 89 in equal quantities may not give you 88.
>
>OK. Can you offer an explanation?
Yes. Assume you bought the 87 in one place, and the 89 in another (two
different marinas).
The exact chemical additive package in each may not be the same (they
probably aren't unless the gas came from the same refineries). That package
affects the total octane of each, and its combination MAY affect the octane
of the resulting mix.
Its NOT LIKELY you'll get in trouble doing this, but I'm somewhat uneasy
trying to second-guess octane/cetane ratings by mixing gas from different
places.
>>You can, however, use this if you have only 87 and 92, for example,
>>available to you and your boat requires 89. If you mixed roughly 50/50
>>in that situation you'd have gas that would almost certainly exceed the 89
>
>Again, please explain. You are implying that the ratio is not an average of
>the two component values.
Its not always; again, you don't know PRECISELY what additive package they
used to get the octane rating you have in there.
Now is it USUALLY. Yes. But I'd err in the side of caution with a marine
engine, simply because in any high-performance application you don't want to
be wrong on the low side.
> The only difference in your example from mine that I
>can detect is that you imply that a .5 octane ratio increment is a good enough
>safety margin. That doesn't clarify why you are rejecting the math I offered.
>
>I said (87 + 89) / 2 = 88. You said "maybe false."
>
>You said (87 + 92) / 2 > 89 with a safety margin for engines that require 89.
>I agree.
>
>But that strikes me as nit picking.
>
>My understanding is that Octane rating represents the ratio of iso-octane to
>heptane as an anti-knock additive in gasonline (as well as some other liquid
>fuels). If you create a 50/50 mixture of two different octane ratings, mix
>them together, the result is an additive ratio that is exactly the average of
>the two additive ratios of the components.
>
>Please, if you have a clear explanation for why I am in error, say so.
>
>Rich Stern
You're assuming that none of the other "stuff" in the fuel has any impact on
the octane rating. But it does. Specifically, the presence (or absence)
of ethanol has an impact, as does the presence (or absence) of various
detergent packages that may be in the gasoline from one supplier and not in
the another.
Consider the case where you get 92 with no ethanol, and 87 with ethanol.
You mix them 50/50. Will you get EXACTLY the midpoint of their octane
ratings? Maybe. And maybe not. You end up with 5% ethanol in the mix
instead of 10% (assuming the 87 has 10% ethanol) and the exact octane
rating of the mixed fuel may be "off" a bit from a pure average.
Its probably never going to bite you, but I'd still use that only as an
emergency practice (ie: some dim bulb fills you with the wrong fuel and
you hear pinging - hopefully before you do real damage. In that kind
of situation you might opt for an octane booster instead - although
I don't know offhand if they're safe to use in marine fuel systems)
(BTW, the US octane rating method is ((research + motor) / 2); there are
others used outside the US another method known as "RON" is frequently used -
the equivalent to 89 R+M/2 is 93 in RON terms. This becomes important if you
go outside the US and find "89 octane" gas that's really 89 RON - that would
be somewhere in the neighborhood of 85 or 86 octane by the R+M/2 method.
Put THAT in an engine designed for 89 octane at minimum and you WILL
get detonation.)
Phoenix
How many marina's , buy their 87 gas from one distributor and their 89 from
another?
How many distributors buy their 87 gas from one refinery and their 89 gas
from another?
--
Jim
1994 Regal 256 for sale - see ad at
http://www.classifieds2000.com/cgi-cls/ad.exe?P61+C189+A0+R1127049+Q25830689
4
To see pictures of the boat's layout visit:
http://www.regalboats.com/htm/boats_commodore_258.shtml
Karl Denninger <ka...@Genesis.Denninger.Net> wrote in message
news:7pld5a$716$0...@dosa.alt.net...
Jerry Bransford
and how simple a 'good as was needed' answer can be, some people will
alwasys go to great lengths to make it FAR more complex than it should
have been, or needed to be. They're the same ones who when a gorgeous
woman says in a sultry voice 'Isn't the sky beautiful tonight?', they'll
disagree and start getting into astrophysics of what the sky really is
LOL!
Jerry
--
Jerry Bransford
PP-ASEL KC6TAY C.A.P.
The Zen Hotdog... make me one with everything!
Marcus G Bell
> Karl, How many marina's , buy their 87 gas from one distributor
> and their 89 from another?
> How many distributors buy their 87 gas from one refinery and
> their 89 gas from another?
I side with Karl here. Even if the gas comes from the same
distributor and refinery, without inside knowledge of the
particular gas you are pumping, you have no guarantee that the
method of achieving the octane levels was as simple as adding
extra booster to the 89, despite what one person said may have
been the case at one distributor.
If you are mixing grades of gas to boost the octane of the low
grade, then you should aim for the result to be a bit above the
desired minimum, just in case the result is not a linear
combination. So if you need 10 gallons of 89, then 6 gallons of 87
and 4 gallons of 92 would theoretically put you there, if the 87
and 92 differ by one parameter only. 5 gallons of each puts you at
89.5 which allows a safety margin just in case the actual
chemistry results in a slightly lower result.
-- -- Marcus. ( be...@mail.med.upenn.edu )
TimePilot
separate marinas.
Phoenix <jfga...@spamfree.mediaone.net> wrote in message
news:YUvv3.424$bj6....@typhoon.southeast.rr.com...
> Karl,
> How many marina's , buy their 87 gas from one distributor and their 89
from
> another?
>
> How many distributors buy their 87 gas from one refinery and their 89
gas
> from another?
>
Marcus G Bell
> Wow... all this just goes to show that no matter how simple the
> question and how simple a 'good as was needed' answer can be,
> some people will alwasys go to great lengths to make it FAR more
> complex than it should have been, or needed to be.
It's not a simple problem, so it requires a complex answer,
especially when the first simple answer is questioned.
Here's the simple answer: yes, mixing different grades of gas is
just fine, if you mix it to a half point or more higher than you
thought you'd get based on the numerical average.
Now, if someone asks me why I say that, I might want to go into
more detail. Maybe that's what happened here.
> They're the same ones who when a gorgeous woman says in a sultry
> voice 'Isn't the sky beautiful tonight?', they'll disagree and
> start getting into astrophysics of what the sky really is LOL!
If the woman is commenting on the sky, it's one thing. If she's
commenting on what gas is safe for an expensive engine, that's
another thing.
Marcus G Bell
> My understanding is that Octane rating represents the ratio of
> iso-octane to heptane as an anti-knock additive in gasonline (as
> well as some other liquid fuels).
A nit to pick, the octane number is not the equivalent ratio of
iso-octane to n-heptane, but the percentage of iso-octane in the
total mix. "87 octane" means a fuel with the same resistance to
knock as a mix of 87% pure iso-octane, 13% pure n-heptane.
Now, what we get from the gas pump is not a mixture of pure
n-heptane and iso-octane. It's a bunch of different stuff, and the
chemistry can be complicated. The equivalent octane rating is
measured in a test engine which can compare the fuel being tested
against mixtures of the pure octane and heptane.
If a fuel of 86 octane rating, we might boost it to 87 by adding
certain ingredients. If we double the additive, do we get 88
octane? Probably not, although the numbers would suggest it. What
matters most is how the stuff behaves in the test engine, so we
are talking chemical reactions with logarithms and exponential
dependencies that need to be considered. Not all octane boosters
are equal, nor is it as simple as mixing "real" octane and heptane
in the lab. The refiner will of course do whatever is financially
expedient to get the actual fuel to behave as desired in the test
engine.
That said, many gas pumps "manufacture" mid-grade gasoline by
mixing regular and premium. They do not necessarily mix them in
proportions equal to the proportional change in octane rating. So
89 is not necessarily a 60:40 mix of 87 and 92. It could very well
be 40:60.
Dale 3
>commenting on what gas is safe for an expensive engine, that's<BR>
>another thing.<BR>
><BR>
Methinks it is better not to have gas around sultry women.
Bruce Edwards
Shreveport Yacht Club
It revealed to me, down in my soul, there were two shooters on the grassy
knoll, we never walked on the moon, Elvis ain't dead, you ain't goin' crazy,
it's all in your head. Let us sing.
David Smalley
>
> Is it OK? I have an I/O V8 Mercruiser 305, 1984.
Yes.
As long as the motor doesn't diesel or ping you are probably doing no
harm, other than that to your pocket book for paying extra for the 89 &
93<G>.
Karl Denninger
Phoenix <jfga...@spamfree.mediaone.net> wrote:
>Karl,
>How many marina's , buy their 87 gas from one distributor and their 89 from
>another?
>
> How many distributors buy their 87 gas from one refinery and their 89 gas
>from another?
Probably few if any.
HOWEVER, that ain't the point - you may try to do this to compensate for
the "wrong" grade you got put in your boat by someone who wasn't paying
attention (perhaps you) at a DIFFERENT marina.
All I'm saying is be safe rather than sorry with octane ratings. You're
better off putting in a NON-ALCOHOL octane booster (watch out - some have
METHANOL in them, and that stuff will corrode the hell out of your fuel
system) than trying to figure out an exact mix between two grades of gas.
Or, for that matter, just put in too much premium in the mix - its safer.
Larry KN4IM
Denninger) wrote:
>
>The exact chemical additive package in each may not be the same (they
>probably aren't unless the gas came from the same refineries). That package
>affects the total octane of each, and its combination MAY affect the octane
>of the resulting mix.
>
(snip)
>--
>Karl Denninger (ka...@denninger.net) Web: childrens-justice.org
Geez, I'm glad I don't have all that lab analysis! I bought "regular"
from Speedway (Starvin' Marvin) on the way home, tonight. It was
$1.059/USGal in Goose Creek (SC), instead of the $1.079 my Speedway
charges......
It all came in on the big, rusty, Hess Oil tanker tied up to the docks
just downriver from the paper mill on the Cooper River. I guess they
were offloading some more, today, as the tanker was sitting low in the
water when I went past in my jetboat. The "Bubbas" on the dock
weren't wearin' white lab coats, so I guess they weren't too worried
about "additives" and "ethanol".
Hess sure had it loaded down. They musta got a great deal from one of
those offshore jobbers down in Antiqua (or was it Aruba??...I fergit).
Hope the ballast water and rust from the old tanker settle out in the
storage tank, tonight, before those trucker/oil analysts/additive
experts pour it into the tank trucks next Monday.....
You know, come to think of it, I didn't see any of those petroleum
engineers driving the independent contractor's oil trucks wearin' any
white lab coats, either!
You don't suppose all the 87 octane dumped in all those different
brand of tank trucks is ALL THE SAME, DO YA?!!!
Larry....Octane bullshit....Proof PT Barnum was wrong. It's every 8
SECONDS.
Larry KN4IM
<jfga...@spamfree.mediaone.net> wrote:
>Karl,
>How many marina's , buy their 87 gas from one distributor and their 89 from
>another?
>
> How many distributors buy their 87 gas from one refinery and their 89 gas
>from another?
>
>--
>Jim
>
How many distributors buy their gas from the LOWEST BIDDER on the oil
market??
ALL OF THEM!
Larry
RBStern
>iso-octane to n-heptane, but the percentage of iso-octane in the
>total mix. "87 octane" means a fuel with the same resistance to
>knock as a mix of 87% pure iso-octane, 13% pure n-heptane.
>
Yes, you are right. The ratio is based on a knock performance equivalent to a
reference fuel mix, not the actual ingredients in the fuel being rated.
I did a little follow up research and came across some extensive gasoline FAQ
documents, on a web site created by a gentleman who runs and maintains octane
measuring engines for a refinery in Southern Cal. (Isn't the Internet a great
thing?)
There is a mind numbing amount of chemistry in the information. Most over my
head. But there is also practical discussion of the implications of the
chemistry. I did come across this reference to octane mixing on his "Gasoline
FAQ Page 3."
"6.15 Can I mix different octane fuel grades?"
"Yes, however attempts to blend in your fuel tank should be carefully
planned. You should not allow the tank to become empty, and then add 50% of
lower octane, followed by 50% of higher octane. The fuels may not completely
mix immediately, especially if there is a density difference. You may get a
slug of low octane that causes severe knock. You should refill when your
tank is half full. In general the octane response will be linear for most
hydrocarbon and oxygenated fuels eg 50:50 of 87 and 91 will give 89."
So, I stand by my original point of (87 + 89) / 2 = 88. However, I must admit
that the original poster's scenario isn't controlled enough to not warrant a
safety margin.
The web site I got the reference from is maintained by a gentleman named John
Runyard. Even if you don't care for the chemistry, the guy is an engine nut.
The engines he works with are very interesting. Good pics, too. The address
is:
http://www.geocities.com/toto?s=76000015
Rich Stern
Karl Denninger
Ding ding ding ding ding! :-)
--
--
Karl Denninger (ka...@denninger.net) Web: childrens-justice.org
Marcus G Bell
> [snip] So, I stand by my original point of (87 + 89) / 2 = 88.
> However, I must admit that the original poster's scenario isn't
> controlled enough to not warrant a safety margin.
Rich, thanks for pointing that out. The information comes directly
from Bruce Hamilton's Octane FAQ, posted periodically to
rec.autos.tech, which I used to follow. Interestingly enough, my
memory indicates that his position was somewhat different several
years ago, more congruous with information I had from elsewhere.
So, it seems my info was out of date.
Given that this has changed over the years, it seems we cannot
take it as a given that gasolines of different octane ratings will
for all time behave as a linear combination of their octane
ratings. For the time being, though, mis your own with predictable
results.
Anyone notice that "87" is like 1.19, "89" is 1.34, and "93" is
1.39? Quiz: Of the three, which is the biggest ripoff?
Phoenix
--
Jim
1994 Regal 256 for sale - see ad at
http://www.classifieds2000.com/cgi-cls/ad.exe?P61+C189+A0+R1127049+Q25830689
4
To see pictures of the boat's layout visit:
http://www.regalboats.com/htm/boats_commodore_258.shtml
Marcus G Bell <be...@mail.med.upenn.edu> wrote in message
news:7pnrpn$ii$1...@netnews.upenn.edu...
Marcus G Bell
> > is 1.39? Quiz: Of the three, which is the biggest ripoff?
Phoenix (jfga...@spamfree.mediaone.net) wrote:
> ahhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh how about 93...... did I
> guess right?
Two ways of looking at it. Say the price should be proportional to
the octane number, so divide the octane by price. You'll find that
87 is the best bargain, 89 is the worst.
Or, say that we start with cheap 85 octane and boost it to 87, 89,
& 93 by adding small amounts of an expensive booster. Under this
reasonable scenario, it's understandable that higher grades should
not be as good a deal, but at the very least the price of a mid
grade should fall between regular and premium in proportion to how
you could mix them to get the mid grade. 89 is 1/3 the way from 87
to 93, so it should cost an extra 1/3 the difference betwen 1.19
and 1.39, over the cost of 87. That would put it at 1.257, which
would be rounded to 1.259, which we call 1.26, but the station
charges 1.34. So, the 89 is again the inferior bargain.
My suspicion is that mid grade is priced closer to premium as an
incentive to buy the premium. "Look, only a nickel a gallon more
than mid-grade, but a lot more octane, wow, what a bargain!"
HarryKrause
I certainly go through these mental exercises while waiting for my turn at
the gas pump.
"Gee, 39 gallons at $1.19, or $46.41...or 39 gallons at $1.25, or $48.75.
Let's see, $48.75 minus $46.41 = $2.34, or...about two bottles of Corona or
a dozen and a half live shrimp for bait or a couple of SlimJims for the
guests to eat."
Decisions. All the time decisions.
--
Harry Krause
- - - - - - - - - - - -
What goes around usually gets dizzy and falls over.
Marcus G Bell
> Me, I am mixing grades because I bought too high and
> unnecessarily expensive grades based ona stupid advice. So now I
> am buying 87 gas.
If your engine runs fine with 87 and does not have a system to
take advantage of higher grades, then anything more expensive is
probably wasted money. If 87 is OK for you, you are fine mixing 87
with whatever higher grade is in the tank now and then filling
with 87 ever after, unless you need to go higher to eliminate
pinging as the engine ages.
There are no harmful effects of mixing grades as long as the
result is as good as or higher than the recommended octane rating.
The mixing must be done thoughtfully if one of the grades is lower
than the recommendation.
Phoenix
You stated that as long as you use the a gas at the rated or higher octane
than you should have no problem. I heard or read (I can't remember which,
they say the mind is the 2nd thing to go. ) that using a higher octane gas
than the engine is rated for is not only expensive, but can also be
detrimental to the engine.
Since I know very little about engines and octane, maybe you can comment on
wither this is fact or BS.
--
Jim
1994 Regal 256 for sale - see ad at
http://www.classifieds2000.com/cgi-cls/ad.exe?P61+C189+A0+R1127049+Q25830689
4
To see pictures of the boat's layout visit:
http://www.regalboats.com/htm/boats_commodore_258.shtml
Marcus G Bell <be...@mail.med.upenn.edu> wrote in message
news:7poqnj$jsk$2...@netnews.upenn.edu...
Marcus G Bell
> Marcus, You stated that as long as you use the a gas at the
> rated or higher octane than you should have no problem. I heard
> or read (I can't remember which, they say the mind is the 2nd
> thing to go. ) that using a higher octane gas than the engine is
> rated for is not only expensive, but can also be detrimental to
> the engine.
> Since I know very little about engines and octane, maybe you can
> comment on wither this is fact or BS.
All right, now that you point this out, there were a few engines
that could be damaged by too high an octane, so the answer depends
on the engine. It is not BS, but not applicable to most engines
either. Thanks for bringing this up. I should have been more
carefull about how I worded my "advice", that is wasn't worded so
as to apply to all engines in general.
An engine management system that includes a knock sensor resets
certain parameters when it senses knock, as may happen if a low
grade of gas is used. More specifically, spark timing is retarded
to eliminate the knock. The converse is that it periodically
advances the spark timing till it senses knock, then pulls back a
bit. This allows it to test if better gas is being used, so that
it can take advantage of the better gas.
As was pointed out by Dave Brown in another thread, early
MerCruiser EFI systems could advance the timing into the range
where pre-ignition would occur, because a limit was not programmed
into the computer. As long as 87 or 89 octane was used, no
problem, because the knock sensor would keep the timing in check.
With premium gas, knock occurs at a bigger advance, so timing
could advance into the pre-ignition range and the knock sensor
couldn't "hear" the pre-ignition. As I understand it, MerCruiser's
response: rather than send out new ECU chips with a proper spark
advance limit, issue a bulletin to the effect of "don't use
premium gas." Pity the uninformed who use premium and hole a
piston.
So, if you have an early MerCruiser EFI, take care that you are
not doing something you shouldn't. Probably most others are not
hurt by high octane, but not necessarily helped either.
Read the owner's manual, actively seek out any updates or service
bulletins which have been issued after the manual was printed,
consult a dealer who has this information. Better than listening
to me, for sure.
Knock (also called detonation): spontaneous ignition of unburned
air/fuel mix in the increasing heat and pressure that occurs AFTER
the spark ignites the mix elsewhere in the combustion
chamber.
Pre-ignition: spontaneous ignition of unburned air/fuel mix in the
increasing heat and pressure that occurs during compression by the
piston upstroke, BEFORE the spark.
HarryKrause
>
> Pre-ignition: spontaneous ignition of unburned air/fuel mix in the
> increasing heat and pressure that occurs during compression by the
> piston upstroke, BEFORE the spark.
>
> -- -- Marcus. ( be...@mail.med.upenn.edu )
I think Eisboch's wife was complaining about that very problem with her
hubby. Spontaneous pre-ignition.
--
Harry Krause
- - - - - - - - - - - -
Flashlight: container for storing dead batteries.
RBStern
>Let's see, $48.75 minus $46.41 = $2.34, or...about two bottles of Corona or
>a dozen and a half live shrimp for bait or a couple of SlimJims for the
>guests to eat."
>
Then factor in the mileage implications. Ten years ago, I had an '87 Honda
Civic that I religously tracked the mileage on. On long highway drives, I
could get 39 mpg on 87 octane. 41 mpg on 91 octane.
The math gets too involved when all variables are considered.
Here's my simple solution formula: If you're flush, buy premium if you think
it helps you. If you're broke and your engine runs ok on 87, that'll do fine,
thanks.
Rich Stern
RBStern
http://www.geocities.com/TimesSquare/Alley/7026/index.html
Rich Stern
Michael J Porter
Marcus G Bell <be...@mail.med.upenn.edu> wrote:
=>RBStern (rbs...@aol.com) wrote:
=>> [snip] So, I stand by my original point of (87 + 89) / 2 = 88.
=>> However, I must admit that the original poster's scenario isn't
=>> controlled enough to not warrant a safety margin.
=>
=>Rich, thanks for pointing that out. The information comes directly
=>from Bruce Hamilton's Octane FAQ, posted periodically to
=>rec.autos.tech, which I used to follow. Interestingly enough, my
=>memory indicates that his position was somewhat different several
=>years ago, more congruous with information I had from elsewhere.
=>So, it seems my info was out of date.
=>
=>Given that this has changed over the years, it seems we cannot
=>take it as a given that gasolines of different octane ratings will
=>for all time behave as a linear combination of their octane
=>ratings. For the time being, though, mis your own with predictable
=>results.
=>
=>Anyone notice that "87" is like 1.19, "89" is 1.34, and "93" is
=>1.39? Quiz: Of the three, which is the biggest ripoff?
=>
=>-- -- Marcus. ( be...@mail.med.upenn.edu )
Interesting, around here (Delaware), it's more like 1.25, 1.35,
1.52 or so. I suspect the high test is so much more expensive
because of the TV commercials that try and lead you to believe your
car will perform "like a tiger" or that really clear gas is best.
Mike