First of all, Maximas never got good fuel economy. My lifetime average
with my 2000 Maxima with 100,000 miles is 21 MPG with a 5 speed. This is
*right on* the revised estimates from:
http://www.fueleconomy.gov/feg/findacar.htm
The old combined mileage rating was 24 MPG for the 5 speed. It is good
to see the EPA got a clue and is posting more realistic ratings. The
automatic transmission 2000 Maxima had a combined rating of 23 MPG but
was recently revised down to 20 MPG under the new testing criteria. If
you beat that in city or mixed driving just count yourself lucky.
That government website also lists the Maxima as using regular gas, but
I know that the actual EPA tests are conducted using the manufacturer
specified fuel (91, in this case) so the listing is just a typo and
shouldn't be ammo in the 87 vs 91 debate. I noticed this mistake in
several cars' listings anyway.
Which leads us to my word on 87 vs 91, for what it's worth:
From the 2000 Nissan Maxima shop manual:
page GI-8:
"PRECAUTIONS FOR FUEL
Use premium unleaded gasoline with an octane rating of at least 91 AKI
(Anti-Knock Index) number (research octane number 96). If premium
unleaded gasoline is not available, regular unleaded gasoline with an
octane rating of at least 87 AKI (research octane number 91) can be
used. However, for maximum vehicle performance, the use of premium
unleaded gasoline is recommended."
page EC-141 lists Low Octane fuel as a possible "Poor Fuel" trouble
diagnosis.
page EC-34:
"The knock sensor retard system is designed only for emergencies. The
basic ignition timing is programmed within the anti-knocking zone, if
recommended fuel is used under dry conditions. The retard system does
not operate under normal driving conditions. If engine knocking occurs,
the knock sensor monitors the condition. The signal is transmitted to
the ECM. The ECM retards the ignition timing to eliminate the knocking
condition."
It is clear from the foregoing that use of 87 octane is not meant to be
done in the long term.
The manual...
says *use premium unleaded*
says use regular when premium is *not availiable*
*does not say* to use regular when I feel premium is too expensive
*does not say* to use regular when I can't feel a difference with the
premium
says low octane is in the same category as *poor fuel*
says the knock sensor retard system is designed for *emergencies*
says the knock sensor retard system is not meant to operate *under
normal driving conditions*
If you pump 87 octane gas expecting the knock system to continuously
retard the timing for you just know it is not meant to be used that way.
Another thing, the phrase "Maximum vehicle performance" does not just
mean acceleration either. It means durability and economy as well. You
affect all of these negatively by putting 87 octane in the tank. Sure
you can *feel* a loss of power and you can *measure* fuel economy, but
how do you know what impact pumping 87 has on durability? Well if the
car is slower and gets poorer mileage you can expect a negative effect
on durability as well.
I also don't care what your local Nissan tech has to say. I have access
to the same training materials and information as he does. His opinion
is no better informed than mine. The engineers are the final word, not
your local Nissan or garage tech. Argue with the Nissan engineers all
you want, I'm not going to. If you pump regular gas *in the long term*,
you are potentially damaging your car for the sake of a few bucks. Not
catastrophically but why do it at all if you don't have to? Besides, the
guys who built the engine don't think it's such a hot idea either.
There are a lot of folks here and on many internet forums who argue
about the value of pumping 91 octane in the Maxima. I am not saying I'm
an expert but neither are they! Unfortunately every piece of advice is
just a guess because your situation contains many factors, some you
don't even know about like gas *quality* and *formulation* (not octane).
Driving habits, altitude, ambient temperature, condensation in the gas,
and seasonal changes to the formulation (in NY they add 10% alcohol part
of the year) will greatly vary the fuel's knock sensitivity and change
tank to tank.
There was a news special on NBC in NY about gas station pump money
errors where the re****ter discovered that drivers were getting premium
gas out of a regular pump when the station ran out of regular. This was
even tested by an expert they brought in because they were looking for
the reverse situation. If that was your car you might be spreading the
gospel of 87 octane not causing a knock without realizing you really had
91 in there the whole time. This happens more than you think because
stations do run out of one type of gas and substitute another because
the wrong truck showed up to fill the station's underground tanks. Of
course, the reverse is possible.
Furthermore, the knock sensor in the Max (and all modern cars)
intervenes to retard the timing *before* the knocks become audible,
making a detonation diagnosis by ear dicey at best. The malfunction
light does not even illuminate when the knock sensor operates (page
EC-392).
Know these facts:
* The Nissan Maxima owners manual and shop manual say to use 91 octane
fuel. Nissan engineers and *not* marketers wrote this. Marketers would
very much like to conceal this fact since it does not help sell a car.
* You may not hear any knocking when running 87/89 octane fuel but that
doesn't mean the computer is not invisibly retarding the timing and
reducing performance (power/economy/durability)
* Retarded timing is *not the most efficient timing* or it would run
that way all the time. Retarded timing will reduce fuel economy as well
as increase combustion chamber temperatures.
Do what you will with this. I decided that the price increase for
premium gas isn't enough to avoid it. As the price of all gas rises the
difference in price shrinks. At least it does near me. My advice is to
run 91 octane and ease up on the lead foot if you need to save gas. It
also saves on wear and tear.
--
Oil is always 15 years from running out, the oceans are always 10 years
away
from rising 10 feet, and the internet always has only 3 years left before
it
runs out of capacity. Color me skeptical.
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