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Originally Posted by phoebeisis
Tom-stopping the motor can save some fuel. My Scanguage tells me
1)Small 4 cyl about .2 gal.hr at idle- 2001 Prizm(corolla) 1.8 4cyl
2)Decent sized V-6 .4 GAL/HR Honda Pilot
3)V-8 ,5-.6 GAL/HR Nissan Titan 5.6 V-8
The Prius seems to use in the .2 gal/hr range.I suspect it uses less, but the scanguage only reads to 1/10th gallons.
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I actually tested the idling rate on my '03 Civic Hybrid when fully warmed up by rolling at in neutral until the instantaneous gauge first pegged "120mpg" at 15mph. That works out to .125 gallons/hr, or 3/4 of a cent per minute at current fuel prices.
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Lots of folks spend an hour a week idling-a V-8 will save 180 gallons($500+) a year if it had a shut down(ignoring AC etc). Luck,Charlie
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180 gallons/yr would mean they were idling an hour a
day. Actual savings for an hour a week would be more like $70/yr.
When it gets down to it, there really is not a whole lot of money to be saved by shutting the engine down at stop lights and such, especially on smaller engines, which would make it difficult for most manufacturers to justify much more expensive starter equipment dedicated for that purpose. In the case of a hybrid system, the motor etc. are already there, and the engine shutoff doesn't cost anything extra to implement.
I suspect mild hybrid systems such as the GM Silverado Hybrid save more fuel with a larger combined starter/alternator by applying necessary accessory loads at more convenient times, such as during braking (and easing off on charging under acceleration) than from actual engine stop. The generator application though is another big plus. I think all hybrids should offer that feature as a "selling point" as it wouldn't cost much to add, and it would be very useful for many people, even in passenger cars, to have reliable 120vAC sockets for camping or whatever. The amount of pollution saved by reducing standalone generator use could actually outweigh the direct fuel savings.