Toyota Prius HSD User Manual download pdf (Page 15)

Seasonal Cycles

All Vehicles

Seasonal cycles affect all vehicles, not just hybrids. But with a Prius, you are much more aware of

the MPG changes due to having a Multi-Display constantly informing you of efficiency differences.

With traditional vehicles, owners typically were not aware how much of an affect climate has on

their vehicle’s performance. They just assume MPG remains relatively constant throughout the

entire year. In reality, that isn’t even remotely correct. Large fluctuations are actually normal.

Temperature &

Lifetime Measure

The difference between the warm & cold months is a significant change in MPG. In the winter, the

engine takes longer to warm-up, and the engine is needed to operate the heater. Both cause more

fuel to be consumed. The density of cold air is thicker, making it hard to push through. This

reduces efficiency. In the summer, running the A/C to keep you cool requires electricity from the

battery-pack. That electricity is ultimately derived from the engine, which consumes fuel to

accomplish that. So, the more you use the A/C, the lower MPG will be.

These examples of real-world data (from http://john1701a.com/prius/prius-data.htm

) clearly the

shows a cyclical effect of efficiency caused by winter and summer (specifically in Minnesota):

The top graph, spanning 3.75 years of time, is a summary of month averages. Below it is data

plotted using individual fill-up points instead. It clearly shows wild fluctuations. These are based

heavily on the influence of temperature. This is why the measure of Lifetime MPG is the only

method for judging true efficiency performance. Long durations will reveal an on-going average

value, which is extremely easy to see by that nearly straight line among the otherwise seemingly

chaotic graph.

Prius User-Guide 15 of 54 Last Updated: 9/01/2007

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Toyota Prius HSD User Manual Page 15