Saturday, July 25, 2009

Optimistic Fuel Consumption Displays - or just another case of "No second chance for first impressions" ?

You finally decided to visit your local dealer in hopes of taking a brand new hybrid for a spin. You get in the car and the salesperson kindly shows you the basics about the vehicle and also clears the MPG-L/100Km trip display and you depart. Along the way, you observe very good fuel economy and the final numbers displayed at the end of the test drive become nothing less than "the cherry on the cake".

you are impressed. And that impression tied in with the unmatched smooth and silent driving experience remains in your mind; tempting and seducing you... at least until a few weeks later at the pump!

OK. Perhaps not all of us purchase a fuel efficient hybrid based solely on the fuel economy numbers we achieve in a first test drive. But, wouldn't many people be tempted to make a purchase decision primarily hinging on this factor alone?

As many of us already know, some hybrids have always been calibrated to slightly overestimate the displayed fuel economy... and now that Honda also appears to have returned to the practice with their 2010 Insight (see our in depth review of the 2010 Insight for details) then why not have it escalate to the next level?

In the case of the new 2010 Prius: How does a 3-7 MPG (US) overestimate sound?
It appears that the discrepancy is larger when highly focused and fuel efficient driving is employed whereas the gap seems lessened when the vehicle is driven in less optimal ways.

How do we determine that "instrumented overestimates" are occurring?

Carefully and patiently top of the tank until you see the fuel level, then reset the trip meter of your choice and drive. At a later date/time, return to your favorite pump and refill to the same level as before and calculate your vehicle's actual fuel consumption by hand. Do this just several times and you will have your confirmation.
NOTE: While topping off an AT-PZEV rated vehicle on a regular basis and in this fashion is not a recommended practice, a few times will certainly not compromise your vehicle's evaporative emissions system.

Wasn't it always like this?

Mostly yes, but still... while some "up or down" deviation is acceptable, this much will inevitably be noticed.


1 comment:

  1. It would be better to have accurate fuel consumption displays, but I have no worries about deviation.
    As a buyer, I will look at the NRCAN ratings to compare the fuel consumption of the cars I am interested in since all cars are tested in the same controlled environment. (Of course, I also look at cleanmpg reviews). If somebody only relies on the in-dash display, then too bad for him/her.
    The fuel consumption display is a very valuable tool to improve your driving behavior, regardless of any deviation (as long as the deviation is consistent, be it 10% under or 5% over).