Sunday, March 30, 2008

Hypermilage Driving

I ran across an article the other day where these fanatic people were getting over 100 mpg using cars that had no special equipment or alterations. I thought - wow, this is just what I need! It so happened that Annie had a practice and a concert in SLC on consecutive days, and so we put some miles on the old Grand Am, and I got a chance to practice some hypermileage techniques.

In case you are wondering how mileage is calculated by the EPA, you can go here. If you follow that page on down quite a ways you will get to the section where the driving techniques are outlines. Note: Not all of these techniques are safe or even legal, not all of them will save you money over all. You might get better mileage if you turn off your car when you wait at a stop light, but the wear and tear on the starter motor, battery and alternator might not make it worth it.

Section II - Basic FE saving techniques
Now that we have a good feel for what others perceive as a problem without knowing what they themselves are achieving, let us begin to consider the ways to match if not beat the EPA estimates.
  • Do not use quick accelerations or brake heavily: This reduces fuel economy by as much as 33 percent at highway speeds and 5 percent around town. EPA tests do not account for this kind of vigorous driving.

  • Do not idle excessively: Decreases average FE. The EPA city test includes idling, but drivers that experience more idling experience lower MPG.

  • Do not drive at higher speeds: This increases aerodynamic drag (wind resistance) and mechanical friction which reduces fuel economy. The EPA test accounts for aerodynamic drag up to highway speeds of 60 mph, but drivers often exceed this speed.

  • Cold weather and frequent short trips reduce fuel economy, since your engine doesn't operate efficiently until it is warmed up. In colder weather, it takes longer for your engine to warm, and on short trips, your vehicle operates a smaller percentage of time at the desired temperature. Note: Letting your car idle to warm-up doesn't help your fuel economy, it actually uses more fuel and creates more pollution. Drive to your furthest destination first and then as you are heading home, stop at the closer destinations in order from furthest to closest as the car is warmed up for longer portions of your drive.

  • Remove Cargo or cargo racks: Cargo and/or racks on top of your vehicle (e.g., cargo boxes, canoes, etc.) increase aerodynamic drag and lower FE. Vehicles are not tested with additional cargo on the exterior.

  • Do not tow unless absolutely necessary: Towing a trailer or carrying excessive weight does decrease fuel economy. Vehicles are assumed to carry three hundred pounds of passengers and cargo in the EPA test cycles.

  • Minimize running mechanical and electrical accessories: Running mechanical and electrical accessories (e.g., air conditioner) decreases fuel economy. Operating the air conditioner on "Max" can reduce MPG by roughly 5-25% compared to not using it.

  • Avoid driving on hilly or mountainous terrain if possible: Driving hilly or mountainous terrain or on unpaved roads reduces fuel economy most of the time. The EPA test assumes vehicles operate over flat ground.

  • Do not use 4-wheel drive if it is not needed. 4-Wheel drive reduces fuel economy. Four-wheel drive vehicles are tested in 2-wheel drive. Engaging all four wheels makes the engine work harder and increases crankcase losses.
Maintain your Automobile: A poorly tuned engine burns more fuel, so fuel economy will suffer if it is not in tune. Improperly aligned or under inflated tires can lower fuel economy, as can a dirty air filter or brake drag.

Try to purchase high BTU content gasoline if available: Fuels Vary in Energy Content and some fuels contain less energy than others. Using oxygenated fuels or reformulated gasoline (RFG), can cause a small decrease (1-3%) in fuel economy. In addition, the energy content of gasoline varies from season to season. Typical summer conventional gasoline contains about 1.7% more energy than typical winter conventional gasoline.

Inherent Variations in Vehicles: Small variations in the way vehicles are manufactured and assembled can cause MPG variations among vehicles of the same make and model. Usually, differences are small, but a few drivers will see a marked deviation from the EPA estimates.

Engine Break-In: New vehicles will not obtain their optimal fuel economy until the engine has broken in. This may take 3-5 thousand miles.

The things that will get you the most good are pretty easy:

Don't drive at high speeds. In airplanes I have been told that drag increases as the square of the speed, and power needed (and fuel burned) as the cube of the speed. I'm not going to get all mathematical, suffice it to say that your mileage will be noticeably lower at 65 rather than 55. I know that traffic won't always let you drive slower, but if you can take a few extra minutes it will save you money. The many large trucking firms are setting their speed limits in their trucks to 62. FYI.

Coast to a stop as often as possible.... within reason. Pushing on the gas until you are close to the stop, then slamming on the brakes costs in gas, brakes, and tires.

Gently accelerate. Imagine you have a raw egg between your foot and the gas pedal.

Generally coasting down hills isn't encouraged... I don't think it is illegal if your engine is running, (don't take my word for it either.... I am no legal expert) but this will help you a lot if you have a long hill. Turning off the engine can be done, but if you aren't careful you might turn the key to far and lock up your steering. And you lose your power steering and power brakes. So this is probably taking things too far. I am pretty sure that turning off the engine is not legal... or smart.

Anyway, driving a 1995 Grand Am with 90,000 miles on a rebuilt engine, fairly well maintained, correctly inflated tires (some of the hyper milers over inflate their tires, which helps with the mileage, but hurts handling, stopping and tire life), with a 5 speed manual transmission and two people in it... we left Maverik in Riverton and drove home. We traveled 104.3 miles, and it took 2.72 gallons of gas to re-fill the tank. Doing the math give 38.35 mpg for this trip. The next day we made the trip back to SLC, and had to drive some on I15 at high speed, with normal traffic acceleration and then back to Maverik. We dropped down to 32.39 mpg for that leg of the trip.

So, I am a fan. I have been driving my Ranger a lot more gently, and found that even with a 4 wheel drive, boxy truck that I can noticeably improve my mileage. If anybody tries some of these techniques, I would be interested to hear from you with a comment.

No comments: