Increase Fuel
Economy with AMSOIL Synthetic Oil
A Look at Fuel
Economy
With no gas price relief in sight, motorists are
looking for ways to stretch their fuel dollars.
As many motorists have noticed, the fuel economy
numbers posted on new vehicle window stickers rarely reflect what is
received after purchase.
Unleaded gasoline prices are currently
averaging $3.40 a gallon, and more than half of Americans say the high
prices are starting to cause them problems. According to a recent
Associated Press-AOL poll, 58 percent of motorists have reduced their
driving, 57 percent have cut back on other expenses, 41 percent have
changed vacation plans and 41 percent are seriously considering
purchasing a more fuel-efficient vehicle.
Vehicles used for towing are notorious
for receiving poor fuel economy, and as many motorists have noticed, the
fuel economy numbers posted on new vehicle window stickers rarely
reflect what is received after purchase. According to Greg Dana, vice
president of Environmental Affairs for the Alliance of Auto
Manufacturers, rather than being derived from road tests, fuel economy
numbers are based on testing performed on a dynamometer in a laboratory
environment. Because pump gasoline from different suppliers and batches
varies considerably, a special 96-octane gasoline called Indolene is
used to ensure consistent test results. According to Dana, the high
octane rating does not affect fuel economy.
Fuel economy ratings are determined by
special computer sensors attached to the tailpipe. By measuring the
weight of carbon exiting the tailpipe, the sensors are able to determine
how much fuel was consumed during the test period.
During the test drive, the dyno is
calibrated to flat conditions and the driver modulates the throttle
according to specific driving conditions determined by the Environmental
Protection Agency (EPA). For the 11-mile city driving test, the vehicle
is driven for 31 minutes at an average speed of 21 MPH. Ambient
temperatures are between 68 and 86 degrees F, and the test includes 23
stops and a 10-minute “heat soak” period where the vehicle is stopped
and the engine is shut off. Six minutes are spent idling, and there are
two one-minute segments where the vehicle speeds up to 50 MPH.
The highway driving test is a
13-minute, 10.4 mile trip at an average speed of 48 MPH and a top speed
of 59.9 MPH. Ambient temperatures are the same as the city test and
there are no stops. Road conditions imitate gently
rolling hills and a combination of rural and interstate roads.
The EPA determined in 1985 that
drivers in real world conditions receive about 90 percent of the city
fuel economy figure and 78 percent of the highway figure. Thus, the
final city value is determined by multiplying by 0.90 and the final
highway value is determined by multiplying by 0.78.
“Once the computer delivers the raw
EPA MPG numbers they are ‘adjusted’ by those multipliers to closer
emulate realworld driving,” says Dana. “Those adjusted numbers are what
appear on the window sticker.”
Small changes in driving habits, road
conditions and weather all have noticeable effects on fuel economy. “A
driver may not notice it, but a vehicle’s fuel economy drops on cold
days because the air is denser and it takes more energy to push the
vehicle through the air than on a warm, dry day,” explains Dana.
Other factors that affect fuel economy
are use of the air conditioner, a heavy load on the vehicle’s electrical
system, engine condition, tire pressure, size and shape of the vehicle
and the load being carried or towed.
Lower axle-gear ratios improve pulling
performance by providing increased low speed torque and improving
acceleration. Though it is a common belief that lower axle gear ratios
have a negative effect on fuel economy, the effect is minimal at worst.
According to Roger Clark, senior
manager for General Motors’ Energy Integration and Fuel Economy Learning
Vehicles Program (ELVP), fuel economy doesn’t change much with an
optional gear ratio. “The typical combined fuel-economy impact, based on
EPA lab test conditions, is about 0.4 MPG to 0.6 MPG between the base
gear ratio (e.g. 3.42:1) and the lowest (e.g. 4.10:1) offered,” says
Clark. “Thatchange is linear. Equipping a truck or SUV with a 3.73 gear
ratio, for instance, would affect combined fuel economy by less than
1/4-mile-per-gallon.”
According to Clark, these fuel economy
changes may not even be detectible during city driving. Lower axle
ratios have more of an effect during long distance freeway driving.
“Most of the axle-ratio changes are going to have a cumulative effect in
fuel economy over time, but it’s going to be very hard to notice any
difference in fuel economy where the vehicle is being driven in a mix of
city and highway conditions,” says Clark.
“The reason we (truck manufacturers)
offer the 3.42:1 and 3.55:1 ratios is those ratios offer the best fuel
economy with a four-speed automatic transmission,” says Clark. “If you
want a truck that responds best to hauling a heavy load or towing a
trailer, then 3.73:1, 3.92:1 or 4.10:1 ratios will provide the best
wheel torque at the lower engine speeds.”
EPA research conducted during the
highway fuel economy test indicates that 54 percent of a pickup or SUV’s
engine power is used to overcome aerodynamic drag. “The best fuel
economy for the typical truck or SUV is cruising right around 40 MPH,”
says Clark. “The EPA test cycle for the highway fuel economy number
averages 48 MPH with a top speed of 60 MPH.”
In a pickup rated at 21 MPG on the
highway, a 10 percent increase in speed over 48 MPH (53 MPH) will
decrease fuel economy by about 1.5 MPG. An average speed of 60 MPH
causes fuel economy to drop another 1.5 MPG. Increasing speed to 70 MPH
brings fuel economy to less than 14 MPG, a 33 percent drop from the
previous 21 MPG.
Aerodynamic and fuel economy research
performed at the Lawrence Livermore National Laboratory and Michigan
Technological University indicates that the added weight and wind drag
associated with towing a trailer forces an engine to work harder and
consume more fuel.
“If you increase driving speed from 50
MPH to 70 MPH, you double the drag force and increase the engine power
required to overcome drag by almost three times,” says Scott L. Post,
Assistant Professor of fluid mechanics at Michigan Tech University.
“Of course, not all of the tow
vehicle’s engine power goes to overcome wind resistance,” says Post. “A
rough estimate is that for cruising on the highway with no hills, about
half of the engine power goes to overcoming drag and the remainder goes
to overcoming rolling resistance.
“When you add a trailer, you add more
wind resistance and more weight, which increases the rolling resistance.
But the overall ratio of drag/rolling resistance may not change much. So
if you are doubling the drag and ground friction when hauling a trailer,
you should expect the mileage to be cut nearly in half as a result.
“The total drag for the
truck-and-trailer combination, however, will not equal the sum of these
two components because the wake from the pick-up will reduce the drag on
the front of the trailer,” explains Post.
The coefficient of drag (CD) for
pickups is between 0.4 and 0.5 CD, while a trailer is around 0.9 CD.
Post estimates total drag for the pickup/trailer combination to be 1.0
CD, but warns that driving in a strong crosswind cancels out much of the
reduced drag resulting from the wake of the pickup.
“The exact amount of drag reduction is
hard to estimate because it will depend on several factors,” says Post.
“For instance, the higher the trailer, the greater the drag, and the
longer the gap between the tow vehicle and the trailer, the less the
wake effect and more drag.”
Post’s studies conclude that every 10
percent increase in drag results in 1 MPG decrease in fuel economy.
The use of
AMSOIL
synthetic motor oils is a proven way to improve fuel economy.
Independent tests show the use of synthetic lubricants can increase fuel
efficiency by two to five percent, while many
AMSOIL
customers report even larger gains.
Fuel Efficiency Tips:
The following tips from the EPA help
motorists receive maximum fuel efficiency from tow vehicles:
1) Avoiding aggressive driving,
including speeding and rapid acceleration and braking, can improve fuel
economy by 5 to 33 percent.
2) Replacing a dirty air filter can
improve fuel economy by up to 10 percent.
3) Repairing engines that are out of
tune or have a defective oxygen sensor can improve fuel economy by 4 to
40 percent.
4) Properly inflated tires can improve
fuel economy by up to 3.3 percent.
T's Advanced Synthetics
Greg and Marcy Thurman
Your Nationwide
AMSOIL
Authorized Independent
Dealer
Nationwide US Warehouses,
Canada and Palm Harbor, FL
727-798-8552
E-Mail:
greg@tsadvancedsynthetics.com
If you
experience problems or have questions or comments about
our website please email us at
greg@tsadvancedsynthetics.com
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