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05-10-2006 07:02 PM #1
Mileage Tips: Engine Start-up & Warm-up
In the Mileage section of this site, you advise drivers not to allow their car time to warm before driving. I disagree.
First, this wears heavily on an engine, lowering its overall efficiency and the efficiency of parts related to it (including pollution controls). Next, most computers enrich the fuel/air mixture in a cold engine to make it burn more effectively and run properly. At idle, this process takes in very little fuel. However, at highway speeds, it requires massive amounts of fuel to move such a large object and make the engine run in a proper manner. Additionally, computer controlls will prohibit a car's torque converter from locking up until the engine has warmed up, making the car run an average of 500 rpm faster to maintain the same speed. In three ways, not allowing a car to warm up destroys fuel economy in both the short and long term.
A similar argument is needed to refute the tip that turning off one's engine while waiting in line at a fast food chain is a good idea. The most damaging process an engine and its associative parts experience is start up. Start up usually involves a temporary poor charge of fuel to get the engine running, thus wasting gas. Only if the car predates the 1990s and the car needs to idle for more than 7 minutes should it be shut down. Also, right after restart, a car engine runs at a higher rpm than at idle. Again, restarting an engine several times greatly increases wear on an engine and decreases efficiency.