Automobile fuel efficiency
Contents
Driving tips
Engine braking vs coasting
In my V6 1997 Passat GLX I found over the years that engine braking got me better mileage than idling during braking. When I started driving a 1999 Audi A4 with a smaller, turbo-charged engine, I found that idle sipped so little gas that it often was better to idle than to engine brake in it. Now that I live in hilly Ithaca, with a 2007 Passat Wagon I have found that the choice of methods of braking depends on the speed and the slope of the hill—Engine braking was only best for steeper hills and/or heavy decelerations.
In all the above cases, the car has had a manual transmission, and I have used the on-board mileage computer to help with the studies.
Engine braking in a gasoline car is best done when rotations per minute are between 2000 and 4000—Higher RPM wear heavily and lower RPM provide little braking or even fight the brakes. See http://en.wikipedia.org/wiki/Engine_braking
Efficient car models
Diesel or electric hybrid?
Why not both? Train locomotives have been series hybrid diesel for decades, but the combination of technologies greatly increases the production cost, so it is rare.
So, if you can only get one or the other, which should you pick? Simply put, diesel will be better for long hauls, electric hybrid for start and stop town driving. You'll see that highway efficiency ratings for diesels are very high compared to similar gasoline models, while city ratings are noticeably higher with hybrids. I, for example, do most of my miles on the open road, so over the year I would do best with a diesel. If we had two cars, a larger diesel for road trips and a smaller hybrid for in-town shopping would be ideal—Well, until they offer diesel hybrids.
Why automakers don't provide North America with their more fuel-efficient models
Automakers claim that Americans don't want the fuel efficient vehicles that people in other parts of the world enjoy. In fact, demand for fuel efficient cars is just not as steady as it needs to be for automakers to be able to plan a release. Model production is planned two to five years in advance, and fickle Americans, on average, only look for fuel efficient models after peaks of gas prices that only last a few months, and those gas price peaks are not predictable in advance of more than 6 months. While there are tens of thousands of us who would purchase a better vehicle, companies don't see that demand as enough to justify devoting production and sales efforts.
Some modifications of models are easy enough to offer as special-order vehicles. For example, in 2007 I purchased a model that normally sold with an automatic transmission. To get a manual version, the dealer here had to send an order, using a published but not well-known code, to the factory in Germany, and I had to wait a month for the car to arrive. The switch to a diesel engine, however, is much more complicated than switching transmissions, since so many parts besides the engine change. Safety and environmental approval may or may not be important issues also.
I, for one, would pay thousands extra to have a much more efficient version of the car I currently own, and it turns out there is such a model available in Europe. I currently drive a VW Passat Wagon with a 2.0 turbo gasoline engine. While VW has decided to remove the wagon from the North American market, it is expanding its offerings in Europe in the fall of 2012 to include a turbo diesel engine and even all wheel drive, and the two combined. I wrote to VW letting them know I'd love to buy one in the US, and they replied that they look at such inquiries to measure interest. Anyone can tell VW and other makers what they really would like to see in the market by contacting them through their web sites. Here are some sites of companies that offer better cars overseas:
If we wanted, we could all be driving diesel-electric hybrid all-wheel-drive super-cars, such is the power of the consumer. Instead, we're mostly driving uninspired cars, and the economics of turnover means we'll be mostly stuck in these for another decade.
Automakers and many consumers equate efficiency with lack of luxury
While the average fuel economy has remained quite low in America, since the oil embargoes of the 1970s there have always been fuel-efficient vehicles from many marques. Small cars like the Chevy Vega were created in the 1960s, in part in response to cheap cars like the VW beetle, but came into their own in the 1970s when gas prices skyrocketed. The way to efficiency in that era was to reduce weight and forward-facing area, resulting in sub-compact, unsafe cars.
Now we have extremely efficient diesel engines, electric-hybrid cars, electronic ignition, and higher average freeway speeds. These changes allow for significant fuel savings in any size car, at any level of luxury. In fact, a large luxury-vehicle that increases efficiency by 20% would save a lot more fuel than a small vehicle with 20% better efficiency driven the same miles, because 20% of a higher number is a higher number. However, in car sales it must be assumed that those willing to pay more for luxury are not as interested in fuel savings as those who buy a cheap car.
What might save us from this poor state of affairs is that environmental concerns are shared by poor and rich alike. Once wealthier Americans who have an interest in reducing their environmental footprint have dealt with their home heating and cooling, which usually leads to their largest impact, they should consider their automobiles. As mentioned above, larger, more luxurious cars have more to gain from efficient technologies.
