Sunday, January 06, 2008

How efficient is a Prius?

I received my brand new Toyota Prius three weeks ago. Technologically, it seems like quite a remarkable car. I say seems because I don't really know much about cars. I can't really tell whether the electrical engine is anything more than a marketing gimmick, especially considering its ridiculously low autonomy (about 1km).

Obviously, the Prius is noteworthy not because of its powerful engine -- its accelerations won't ever rivet you to your seat -- but because it is supposed to use little gas. Anyway, after three weeks of driving, today it alerted me through a blinking square on the dashboard that it needed a refill. When I brought it to the gas station, her odometer was showing 670 km. Her tank was full after drinking 41.25
liters of unleaded gasoline, which brings me to my main point.

Assuming the gas tank was completely full when I got it (which is somewhat an iffy proposal), my Prius yielded an average of 6.1 liters for 100 kilometers. By the way, 6.1 l/100km is equivalent to 38.56 MPG (US gallons). This result is considerably worse than the mileage advertised by Toyota, i.e. 4.4 liters per 100 kilometers, i.e. 53.46 MPG. Nevertheless, the Prius still emerges as being more fuel efficient than most other cars.

Of course, a single measurement is not necessarily representative, especially considering that those 670 km included a drive to a nearby mountain. After googling for a few minutes, I stumbled upon a US-governmental page showing the MPG obtained by other drivers . My MPG happens to be worse than the average shown on that page.


The second time around, I measured 810 km for 42.02 liters of unleaded gasoline, or 5.2 liters per 100 km (45.3 MPG). This result is very much aligned with the average reported by other drivers. It could probably be improved, as the 810 km included a trip to a nearby mountain.

The difference with the first result can be explained by the fact that on the highway I now drive a little lower than the authorized limit, at 110 km/h instead of 120km/h.


Anonymous said...


By Toyota Prius, do you mean , "Prius Hybrid" ? I ask because the word "prius" is not present in your text. I assume yours is a hybrid car.

And, yeah if that's a hybrid, then they are suited best to the heavy traffic at the city, i.e. when the cars move in short "stops & drives" (we say so in our native language) in a traffic jam.

Such traffic jams are mostly seen in densely populated (or unhealthily civilized) cities. A good example could be Istanbul, where I live. But also in uniformly populated and healthily organized cities like Berlin there's a problem: There are a lot of traffic lights in almost every roundabouts and anyone driving inside the city must spent a significant portion of the time waiting at those traffic lights...

Both these cases and the like will cause a huge losses of time and gas (contributung further to the profits of the oil giants) and deteriorating the health of both cars and the people.

At heavy traffic conditions and short distance travels a hybrid would be perfect choice, not only because it would consume less, also because it would produce less noise during the stops.

For long distance and out of the city trips diesel engines might fit better. A 59 kW Volkswagen Polo BlueMotion with its official statement "3.2 liters of diesel consumption per 100km" could outperform even those hybrids.

Ceki said...

Thank you for your comments.

As of this writing (i.e. April 2008), the Toyota Prius corresponds to one and only one model which is hybrid. For all practical purposes, the Toyota Prius is synonymous with hybrid cars. However, that is very likely to change in the near future.

Anyway, most people are misled to think that the Prius is only fuel-efficient within cities. Actually, its combustion engine uses the Atkinson cycle instead of the more common Otto cycle. For a given engine size, the former is less powerful but more fuel-efficient than the latter. Consequently, the Prius is more fuel-efficient than most cars, not only within cities but also on highways.

geoffh said...

Yes, I can confirm that the Prius is also more fuel-efficient on highways. I live about 45 (highway) miles from my office, and when I started driving my 2008 Prius 7 months ago, I was getting about 45-50 MPG, compared to 31 in my 1997 Acura Integra.

Another great benefit of the Prius is its consumption feedback on the dashboard monitor. It has helped me to gradually increase my highway efficiency to around 55-60 MPG through experimentation. I find that the optimal speed is around 55-60 MPH (~90-100 KPH), that using the cruise control feature yields a 5-10% boost in efficiency.