http://millp002.wordpress.com Just another WordPress.com weblog Tue, 27 Oct 2009 21:39:59 +0000 en hourly 1 http://wordpress.com/ http://s2.wp.com/i/buttonw-com.png http://millp002.wordpress.com http://millp002.wordpress.com/2009/09/29/hello-world/ http://millp002.wordpress.com/2009/09/29/hello-world/#comments Tue, 29 Sep 2009 22:37:22 +0000 millp002 ]]> For a long time now I have frequently heard people say that they use cruise control to save fuel in their car. They still constantly complain about their poor fuel economy. While cruise control may reduce fatigue due to constantly having to adjust the accelerator pedal, if you are not driving on a nearly straight perfectly level road then it will actually make you use more fuel possibly a lot more. For example, I recently purchased a used 2005 Jeep Liberty, with the V6 engine. After hearing several people remark about how poor the fuel economy of these were I decided to check it out for myself. After a week of driving during which my wife and I both spent similar time behind the wheel the MPG was arround 17.5. While this is not horrible, it could be better. So I decided to try installing a high efficiency air filter. This should have improved the fuel economy by a few percent. But after a week of my wife commuting to and from school, and me not driving it at all, I recalculated the fuel economy and was very disappointed when it turned out to be only 15.2 MPG. Puzzled; I tried and tried to figure out how this was possible. After some discussion with my wife she stated that she used cruise control so that she could save gas. Bingo! Well there’s youre problem, I told her. Because of the hilly terrain between our house and her school, even though she was on the freeway, the curves and hills cause the cruise control to use more fuel. She did not believe me, but after a while I convinced her to at least try driving for a week without using the cruise control. At the end of the week I recalculated her fuel economy and came up with 21.4 MPG. Now that I can live with. The reason that cruise control made the Jeep use more gasoline is simple really. It tries to maintain a constant speed regardless of the terrain the road crosses. People can react to changing terrain in advance. For example if you are coming up on a curve you can take your foot off of the accelerator pedal and let the car slow down gradually. The cruise control will maintain constant speed until you apply the brakes at the last minute. that will also cause you to have to brake harder and thus wear out your brakes faster. Also, when approaching a hill a human will normally accelerate gently to gain a little speed before reaching the hill, and would not be that concerned if the vehicle lost a little speed on the way up. The cruise control will not react until the vehicle has slown down by a few miles per hour, and then it will pin the throttle wide open trying to regain lost speed. So, cruise control, even though it may save some gas in some situations like flat straight road it can also have the opposite effect.

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