Filter
Top Products
UNDERSTANDING
MPG Measurement
Lifetime
LIFETIME is the most useful measurement. Total miles driven, divided by total gallons consumed,
informs you how efficiently the car has performed overall.
Tank
TANK is the measurement between each fill up. You press the RESET button when the tank is
full. The results are informative, but not perfectly accurate. In cold weather, the bladder inside the
gas tank shrinks. This reduces the overall capacity making the "full" level variable. Also, "full"
can be misrepresented if the pump doesn't shut off at the proper time. These factors make
calculations based on fill-up less accurate.
Trip
TRIP is mostly for fun, since a multitude of variables can affect the measurement to a single
destination. Watch the 5-minute summary segments shown on the multi-display. Remember
though, if you were to start a drive downhill, with a tail wind, a warm engine, a fully charged
battery-pack, and a warm outside temperature, the MPG would be very impressive for that
particular trip. But then if the return trip back was uphill, against the wind, with a cold engine, a
drained battery-pack, and a cold outside temperature, the MPG would appear very disappointing.
In summary, trip results can vary greatly. The overall average is what really matters.
Sudden Drop
Tire pressure may have dropped. For every 10 F degrees colder, pressure will automatically drop
1 PSI. Verify you still have as much air in the tires as you think they do.
Increased use of the heater or air-conditioner (which includes the defroster) will force the engine to
run more often. Try a less demanding setting.
When the temperature drops below freezing, you may notice the engine has to run quite a bit longer
to warm up the catalytic-converter. This is to keep the Prius emissions Super-Ultra low. Avoid
driving short trips; instead, take advantage of the time after warm up is complete by running several
errands at once.
A dirty engine air-filter will also cause the MPG to drop. Check it routinely, especially as the
seasons change. Once flow becomes visibly restricted (dark colored rather than white), the time
has come replace it.
Tire Break-In
Don’t forget that new tires require a break-in period. Before that the tire surface and tread edges
will be rough, causing MPG to be lower than you expect. It takes about 1,000 miles (1,600 km)
before enough wear (barely visible to a trained eye) occurs to allow less abrasive contact with the
road. And since front tires wear more than those in the rear, expect another break-in period the first
time the rear tires are rotated to the front. Fortunately, that reduced MPG will only last a few
hundred miles.
Increasing MPG
A/C & Heater
Minimal use is the key. Using the Heater or the A/C (which includes the defroster) on anything but
a low setting may prevent the engine from shutting off. That will reduce MPG. So, try to avoid
high demand use. Fortunately, on the highway using the A/C is still more efficient than opening
the windows.
Prius User-Guide 9 of 45 Last Updated: 2/07/2006