Premium Vs Regular
The bottom line - Most cars don't need premium, but a few do -- and not necessarily the ones you'd expect. And premium's not likely to "clean" your engine, either...
Premium
vs. Regular Gas: How to Decide
The Bottom Line Most cars don't need premium, but a few
do -- and not necessarily the ones you'd expect. And premium's not likely to
"clean" your engine, either. While many people claim that their car runs better on premium, this
costly fuel is really only needed in a few circumstances. However, when it is
needed, it must be used to spare your engine from costly damage. On the other
hand, if you burn premium when your car doesn’t need it, the damage won’t be to
your engine but only to your pocketbook.
It’s All In The Numbers
The AKI (anti-knock index --
also known as "octane rating") of the fuel is an average of two different
methods of computing the fuel's ability to resist engine knock. Regular unleaded
gas in the U.S. has an anti-knock index of 87, while mid-grade is usually 89,
and premium typically is 91 - 93. The higher the number, the more anti-knock
protection the fuel offers.
Engine knock occurs when the
fuel in the cylinder ignites by itself before the spark plug ignites it. The
technical name for this condition is "pre-ignition." It sounds like marbles
rattling around in a can, and it generally gets worse the harder you press on
the accelerator pedal.
Knocking can indeed damage an
engine because what is in effect happening is the "explosion" of the fuel/air
mixture is trying to push the piston downward in the cylinder before it's gotten
to the top of its stroke and is free to move downward. The engine is actually
working against itself to a degree, and there is a lot of mechanical stress
placed on certain engine parts, such as the pistons. In extreme cases, knocking
can burn holes in the pistons and create other forms of engine damage.
Oil companies sell higher AKI
fuels (also known as premium) to address this problem. A fuel with a higher AKI
actually burns more SLOWLY than fuel with a lower AKI. This is because the fuel
is less volatile and requires more heat input before it begins to ignite.
(For this same reason, high AKI
fuels will actually make your car HARDER to start on a very cold day. In extreme
cold -- below 0 degrees F -- you want a more volatile fuel which ignites easily
so you can get the engine going without extensive cranking. So if extreme cold
is expected, buy 87 AKI gas unless your owner’s manual advises against it.)
Who Needs Premium?
Basically, all premium fuel
does is resist knock. So the short answer to the above question of “Who Needs
Premium?” is simply any vehicle whose engine knocks without it. Consider these
guidelines as you decide whether you really need premium or are in the majority
who do not:
1. If your
vehicle makes the above-described knocking sound when you accelerate, try the
next higher grade when you refuel, and then see if the knocking goes away. If it
does, stick with that grade. If not, bump it up another grade the next time you
get gas. Generally speaking, high mileage vehicles with a lot of carbon deposits
in the engine are likely candidates for needing premium or mid-grade gas, since
these deposits reduce the volume of the engine's combustion chamber and make
knocking more likely. In addition, the carbon deposits themselves get hot and
may act to ignite the fuel if lower AKI fuel is used. High mileage engines do
not always have carbon deposits; those that have been driven mainly in town and
done a lot of idling are most likely to be “carboned up.” My Ford F-150 has
210,000 miles on it and does not knock on 87 AKI regular unleaded, so that’s
what I use.
2. If your
owner's manual calls for higher AKI fuel, use what the Good Book says. Usually
this will be specified by manufacturers of high compression, high performance
engines. If lower AKI fuel were used in these engines, performance would suffer
because the engine's computer system would have to retard the ignition timing
(reducing horsepower and fuel economy) to keep the engine from knocking.
If, in such an engine, the
computer could not retard timing enough to keep it from knocking, the engine
itself could be damaged. This would not be likely to happen on one tank of fuel,
however. So if you lend your BMW to your son or daughter who has a hot date,
don’t run for the siphon hose if he or she returns it with a full tank of
regular unleaded. Just drive more easily than normal so the engine's maximum
performance isn't needed, and there should be no problem.
But I Want to Keep My Engine
Clean!
The higher AKI of
premium gasoline does not in itself make it any cleaner than regular gas. Oil
companies, however, like to advertise that their premium fuels are ‘specially
formulated” to clean fuel injectors, restore lost power, and, hey, maybe even
improve your sex life. But the truth of the matter is that any “cleaners” that
could be added to gasoline itself are probably not going to be present in
sufficient quantities to do much good.
A better strategy to keep your
fuel injectors clean is to buy your gas from reputable stations that have a
relatively brisk business. In this way the gasoline is liable to be freer of
water and other contaminants. It’s also not a bad idea to avoid buying gas from
stations while their tanks are being filled by a big tanker truck. It’s possible
that the filling process could stir up gunk that’s settled to the bottom of the
station’s storage tanks and make it more likely that debris could wind up in
your own tank. (Gas stations have filters that are supposed to prevent this, so
this is a minor point for those who want to be extra careful; it’s not a really
big deal.)
“But I Just
Think Premium Makes My Car Happy”
If you enjoy using premium
because you think it makes your car “happy,” then go right ahead and use it.
President Bush has asked Americans to spend money to support the economy, so you
can view it as your small patriotic contribution. And if you own stock in an oil
company, so much the better. Using fuel with a higher AKI than needed will in no
way harm an engine. Also, your engine won’t get “a taste” for the good stuff and
rebel against you if you fall on hard times and have to use cheap gas.
Alcohol: The Tough
Question
No, this isn't a
lecture on drinking and driving. Ethanol is a type of alcohol that is often
added to fuels to increase the AKI rating. Government regulators like it because
they claim it helps engines burn cleaner. Should you use it?
This is a more complex question
than what AKI rating to use. Alcohol-gasoline blends may make a car do better on
an emissions test, so if you need one to get your car licensed in your state and
are afraid your car may not pass, fill your tank with an ethanol blended fuel
before you take it for its emissions test.
Whether these blended fuels
actually keep any pollution out of the environment is not as certain. This is
because emissions tests don’t necessarily take into account the fact that your
car may burn more fuel if you use an ethanol blend. On a per-gallon basis, a car
will emit fewer pollutants with an ethanol blend fuel because ethanol burns more
cleanly than gasoline. But on a per-mile basis -- the only basis that matters --
an ethanol blend fuel might not be any cleaner than gasoline because cars
typically get worse gas mileage with it than with straight gasoline.
For example, if you get 30
miles per gallon with straight gasoline, and 28 miles per gallon with an ethanol
blend fuel, for every 1000 miles you drive, you are burning a little over two
more gallons of the ethanol/gas blend than you would have burned if you had used
straight gasoline. So even if the ethanol/gas blend burns, say, 5 percent
cleaner than straight gas, you are still actually polluting more with the blend
because you’re burning almost 7 percent more fuel.
There are other issues as well:
Ethanol has a tendency to degrade rubber fuel system components such as gaskets.
While late model cars have supposedly been made with gaskets that resist damage
from ethanol, some older models may not be so resilient. What can happen is
little pieces of rubber that have come off of deteriorating gaskets can find
their way to fuel filters or fuel injectors and gum things up.
All in all, for the environment
as well as most vehicles, ethanol in gas is probably not going to do much harm
or much good. But on the off chance that it may, I personally prefer to avoid
it. Trouble is, in a lot of states, stations do not have to tell you if their
gas has ethanol in it. You can, however, look for stations who advertise their
fuel as “100 percent gasoline” or similarly.
(These comments do not apply to
newer dual-fuel engines that designed to run on either gasoline or methanol. If
you have one of these engines and use methanol, follow owner’s manual
recommendations.)
In
Summary
Fuels with a high
AKI number are needed in a few cars, but the majority will run fine on regular
unleaded. If your car knocks when you accelerate, or if your owner’s manual
calls for a higher AKI, use one of the premium grades. Otherwise, regular
unleaded will save you
money and reduce your driving costs.
Source: www.epinions.com
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Gas Saving Tips
Here are some tips to help you reduce the amount of gas you use. If you are already following these tips, you are probably getting the best gas mileage your car can deliver.
Gas Saving Tips
Here
are some tips to help you reduce the amount of gas you use. If you are already
following these tips, you are probably getting the best gas mileage your car can
deliver.
Keep
Your Engine Properly Tuned
Fixing
a car that is noticeably out of tune or has failed an emissions test can improve
its gas mileage by an average of 4 percent, though results vary based on the
kind of repair and how well it is done.
Fixing
a serious maintenance problem, such as a faulty oxygen sensor, can improve your
mileage by as much as 40 percent.
Drive
Sensibly
Aggresive
driving (speeding, rapid acceleration and braking) wastes gas.It can lower your
gas mileage by 33 percent at highway speeds and by 5 percent around town.
Sensible driving is also safer for you and others, so you may save more than gas
money.
Fuel
Economy Benefit: 5-33% Equivalent Gasoline Savings:
$0.12-$0.76/gallon
Observe
the Speed Limit
While
each vehicle reaches its optimal fuel economy at a different speed (or range of
speeds), gas mileage usually decreases rapidly at speeds above 60 mph.
As
a rule of thumb, you can assume that each 5 mph you drive over 60 mph is like
paying an additional $0.20 per gallon for gas.
Observing
the speed limit is also safer.
Fuel Economy Benefit: 7-23% Equivalent Gasoline Savings:
$0.16-$0.53/gallon
Remove
Excess Weight
Avoid
keeping unnecessary items in your vehicle, especially heavy ones. An extra 100
pounds in your vehicle could reduce your MPG by up to 2%. The reduction is based
on the percentage of extra weight relative to the vehicle's weight and affects
smaller vehicles more than larger ones.
Fuel
Economy Benefit: 1-2%/100 lbs Equivalent Gasoline Savings:
$0.02-$0.05/gallon
Avoid
Excessive Idling
Idling
gets 0 miles per gallon. Cars with larger engines typically waste more gas at
idle than do cars with smaller engines.
Use
Cruise Control
Using
cruise control on the highway helps you maintain a constant speed and, in most
cases, will save gas.
Use
Overdrive Gears
When
you use overdrive gearing, your car's engine speed goes down. This saves gas and
reduces engine wear.
Note:
Cost savings are based on an assumed fuel price of $2.31/gallon.
Source: www.fueleconomy.gov
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