The First Easy Way to Improve Gas Mileage
Change Driving Behavior
The easiest way to improve gas-mileage is to change
the driver. Aside from going on a severe diet, drivers can change
the way they operate the car. This called 'hypermilling.' Various
sources claim a 25-33% improvement in gas mileage. The usual gas
saving tips aren't any more helpful than they are obvious. What
drivers need are some immediate positive or negative feedback on
their actions. There are devices that do this with much more grace
than a back seat mother-in-law.
These driver feedback devices all plug into the Onboard
Diagnostics Port (OBD II port). The OBD II port is always located
near the driver's left foot at the base of the dash. All of these
devices that utilize the OBD port can also diagnose check engine
lights. If the check engine light comes on you can find out exactly
what is causing it. That alone will pay for the product after two
or three check engine lights.
I think it's important to understand that all of these
devices here only show calculated fuel consumption. They cannot
measure the actual fuel consumption. The calculated fuel consumption
is based on a few known parameters such as mass air flow, manifold
air pressure, engine rpm, and then assumes are few things such as
a constant 14.7 air to fuel ratio, a constant volumetric efficiency,
and sometimes a correction factor is thrown in. In other words,
these are NOT accurate. But they are precise. It's possible to repeat
the conditions and get the same result. And the accuracy is 'good
enough' for the average user. Just keep in mind that if you see
99mpg or 300mpg for a moment, it isn't necessarily true.
This little device costs about $250 and advertises
savings of $500+ after one year. It has a color screen with pretty
graphics. It constantly grades the driver on the Kiwi score while
monitoring four (up to 26) vehicle parameters. The Drive Green mode
shows drivers how to maximize efficiency through lessons. The Kiwi
also diagnoses check engine lights. If improving gas mileage through
altering your driving habits is the primary goal, this is the tool
The premium option is the DashDAQ. The $700 price
tag let's everyone know it (it can be had for about $550 if you
shop around). The DashDAQ is a small Linux computer with a bright
color touch screen, multiple open source programs for monitoring
vehicle behavior, and all the connections necessary to connect to
any original or aftermarket engine management systems. What puts
the DashDAQ on this list is the Fuel Economy program that functions
somewhat like the Kiwi. Other programs include, engine diagnostics,
custom gauge display, data logging (from over 2000 parameters),
drag strip test, 0-60mph braking test, Dynamometer, a lap timer
(with GPS option), and an optional GPS system.
This is a very powerful tool and compares somewhat
to the DashDaq. But the interface is a much simpler black and white
screen with buttons to the side. What puts this device in this list
is the ability to measure a calculated instant and average fuel
economy. It also has a dynamometer program, engine diagnostics,
data logging, sensor data display, and custom sensor inputs. It
also records GPS data from an external GPS system. The Auterra Dashdyno
can be purchased for $300 to $400 depending on where you shop.
At $170 this is the least expensive option. It does
what the Kiwi does but with a lot less class. Four buttons and a
small display just big enough for abbreviated words shows why. Despite
its appearance, however, it is a very capable device. It monitors
calculated fuel consumption, and can display a variety of live vehicle
data. Like the other devices it is also diagnoses check engine lights.
For Cars Built Before to 1996
If your car was made before 1996 and is not OBD II
compliant none of these devices will work for you. But don't lose
hope just yet.
For cars made before 1996 there's another option out
there. A simple vacuum gauge. The vacuum gauge monitors air pressure
in the manifold. If the engine is moving a lot of air (and fuel)
at high rpm, the air pressure in the manifold will be about equal
to the atmospheric pressure and the needle would point to maximum
(0 inches of mercury). If the engine is cruising down the highway
under low stress, then the engine will pull a strong vacuum in the
manifold. The needle on the gauge may read below 20 inches of mercury.
To conserve fuel, change your driving behavior so that the needle
Accelerometers measure changes in acceleration. There
isn't a way for these devices to measure or monitor gas mileage.
It is possible to use these for a calculated guess as to how much
power the engine is generating. I don't have much faith in the accuracy
or repeatability of these. For iPhone users there is iRev and Dynolicious.
For $200+ these iPhone apps can be connected to the OBD-II port
for more vehicle data. But glory is fleeting. Technologies like
the iPhone are superseded in months, and the old software may not
work with the new iPhone. This was a problem I had with Injectoclean's
diagnostic tool for the Handspring Visor. The original Visor's are
now part of our fossil record!
Other accelerometer devices include the G-Tech Pro
and RaceLogic systems. The G-Tech Pro is an inexpensive consumer-oriented
windshield mount device. The RaceLogic system is a professional
racetrack telemetry system. These are used by automotive journalism
such as Road and Track.
Gas Saving Tips
Don't go over the speed limit. Air resistance increases
with speed. An increase in fuel consumption will be required to
Accelerate before the hill, and then coast up letting
the car naturally decelerate as it reaches the top. This reduces
the work an engine has to do to climb a hill.
Remove excess weight. Kicking out passengers that
won't split the gas bill is a good way to reduce weight.
Stay in a higher gear to keep the engine rpm low.
This works really well with a few engine modifications like an engine
reflash and some bolt-ons to improve low-end torque.
Cruise control does help. Cruise control maintains
vehicle speed, not low engine speed. In most cases the cruise control
will change engine speed less than the human driver that results
in a gas mileage benefit. A vehicle moving at a constant speed stores
kinetic energy that reduces the work an engine has to do.
Keep tires properly inflated. Look on the inside of
the driver door (near the latch) for proper tire pressure. If the
car is front heavy like most front wheel drive cars, keep the rear
tires under less pressure than the front for better rear traction.
A difference of more than 10 psi between the front and the rear
is excessive. Use careful judgment. If you're not sure, keep the
pressure the same on all four tires.
Get an alignment. Energy is being wasted if all the
wheels aren't pointed in the same direction.
Drive relaxed. The Mythbusters TV show had a great
episode where they compared the gas mileage between angry and relaxed
drivers on a closed course. The relaxed driver used 33% less fuel
than the angry driver.
Keep the tailgate up on your pickup. This was on Mythbusters
What NOT To Do
Don't shut the motor off during a stoplight. That
would be a great way to find out that the battery just died. In
fact, you'd let everyone else behind you know that your battery
died. And then the police would show up to point out the idiot who
turned their car off in traffic. And then you can pay for a tow
truck and a new battery.
Don't use low rolling resistance tires (LRR). These
are dangerous. If the car can't stick to the pavement then your
steering a sled. The car needs to adhere to the pavement to brake
and turn effectively. Seriously, don't use LRR rated tires.
Don't accelerate toward a stoplight. That's what New
Don't accelerate really really slowly. It
saves about 1% at best when compared to normal or brisk acceleration.
Don't avoid the gas station. Driving on empty won't
extend your gas mileage. It may prolong the moment the credit card
is swiped at the pump, but it won't change the amount you pay per
mile. You'll pay the same amount per mile if you fill up every 1/4
tank or every 3/4 tank. If you run out of gas you better have a
close friend with a gas can and time to spare. Or pay $100 for a
Step 2: Reprogram
Step 3: Improved Maintenance
Wiper Arm Adjustment
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