Our latest mileage challenge took three hybrids — the Honda Insight, Mercury Milan Hybrid and Toyota Prius — and one diesel, the Volkswagen Jetta TDI, from Chicago to Fond du Lac, Wis., and back. The total distance came to just over 300 miles: The first 38 miles were in urban gridlock, the next 230 miles or so consisted of relatively open highway driving and the final 35 miles took place in afternoon interstate traffic.
Three of our contenders had automatic climate control. We set all three at 68 degrees and hit “Auto.” Ford and Toyota told us their air conditioning would run continuously in automatic mode, but both systems use electric air-conditioning compressors that don’t ding gas mileage as much. Conversely, the Insight has a conventional hydraulic compressor, but Honda said it runs on an as-needed basis when you hit “Auto.” That left us with the Jetta TDI, with a manual system that also uses a hydraulic air-conditioning compressor. We scratched our chins, considered our options and settled on leaving the temperature dial at 68 degrees, the fan at half-speed and the air conditioning on. That sounded about right to us.
A further wrinkle: The Prius and Insight both have economy modes that optimize everything from the drivetrain to air conditioning for better gas mileage. (The Prius also has Power, EV and Standard modes; the Insight just has Economy and Standard.) We’d have left both in Standard mode, except the Insight defaults to Economy whenever you restart the car. It stands to reason that most drivers will acquiesce to that, so we did the same — and, to compare apples to apples, we put the Prius in Economy mode, too. (The Milan Hybrid doesn’t have any such programs. It proved refreshingly simple.)
All four cars had trip computers with gas-mileage readouts, which we reset to start each leg. Our varied route gave us a chance to see how each one did, especially given their EPA ratings. The Prius and Milan Hybrid are rated higher in the city, while the Insight and Jetta TDI are rated higher on the highway. Comparing two extremes — 38 miles of urban gridlock during Leg 1, with average speeds around 20 mph, versus 71 miles of interstate driving for Leg 2 at average speeds of 59 mph. Here’s what each car’s trip computer reported:
- Insight: 52.5 mpg urban, 54.0 mpg highway
- Milan Hybrid: 45.1 mpg urban, 43.9 mpg highway
- Prius: 67.0 mpg urban, 60.5 mpg highway
- Jetta TDI: 38.5 mpg urban, 48.3 mpg highway
We won’t spill the beans yet, but there’s more to the story. Suffice it to say the fill-ups at day’s end yielded some unexpected results. Stay tuned for more.
Previously: Mileage Drive 5.1: Hybrids vs. Diesel