The question of how long to leave an engine idling at a stop
vs. restarting it - and which uses more fuel - came up in this thread:
Pulse and Glide questions..Totally new to this
But I figure it's worth its own thread.
IWillTry wanted to know the same answer, so he
systematically measured fuel consumption @ idle, and compared it to the fuel consumed performing a warm restart.
His observations (based on a 1.0L gas engine with throttle-body injection):
Quote:
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If you begin to extract useful work from your engine within 1 second of starting it, then the additional fuel consumed by restarting your engine is equivalent to about 0.2 seconds of idling. So you don't even need to consider how long you might be stopping for. If you're interested in reducing fuel consumption, turn your engine off whenever you can, and don't turn it back on till just before you need it. If you're a typical city commuter this can increase your mileage by around 10%.
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He makes the same caveats about starter wear.
See his
full report on iwilltry.org.