Care to try making your car a "Homemade Hybrid" with the ten second rule?
Kristin, a contributor to Celsias.com has done a bit of research online, as well as some real-world testing to come up with what she is calling the "Homemade Hybrid" ten second rule. The idea is to shut your car off and restart it manually whenever you stop for a stop light where you expect to be sitting for more than ten seconds. I have heard of the old rule that it takes three minutes of stopping the engine to save the gas it takes to restart the car, and have thought that seemed like a long time. Kristin correctly points out that the constant starting and stopping may wear out the starter a bit faster, but that difference would most likely be made up way before it came time to replace the starter. In her own testing, Kristin found that she saved a whole gallon of gas, or about 30 miles of driving extra per tank of gas by implementing this technique. Anybody else out there care to give it a try?
Edit: Changed the word "less" to "more" - thanks Howard!
[Source: Celsias.com]
Reader Comments (Page 1 of 1)
wayne 10:22PM (6/21/2009)
i do same thing now for past couple months, except i installed a click off and click on switch on my gear shifter, i have a saturn sc 5 speed, i dont turn off key, as i approach a hill i can coast, one click and engine shuts off, clutch in
as i get to end of coasting, clutch out and hit switch again, car starts and away i go, somewhere around 5-6 mpg more from doing this, ill take it,
plus, its kinda fun to do
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Leszek Pawlowicz 2:35PM (3/29/2007)
I do that as well, but use 30 seconds as my criterion. The break-even point for modern fuel-injected cars is 10 seconds; for older cars with carburetors, it's longer than that, but probably not 3 minutes. The Canadian government says that shutting down you engine when you'll be standing still for 30 seconds or more adds about $7 a year for the average car in increased maintenance costs because of the increased wear and tear on the starter, but you save far more than that in fuel costs alone.
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Howard Lee Harkness 1:19PM (3/29/2007)
"...whenever you stop for a stop light where you expect to be sitting for less than ten seconds."
Did you perhaps mean MORE than ten seconds?
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Robert 6:05PM (3/29/2007)
I'd be careful in areas with lots of traffic lights. It seems like you could easily drain your battery if you don't do enough driving in between turning the car off.
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Larry Rose 3:10PM (3/29/2007)
Ive been doing this for years, and it does make about a 5 MPG difference in my car. I key off for coasting (which I do a lot of), and try to bump start (manual transmission) when I can to not use the starter, or spend the electricty. My 1 tank record is 46 MPG in mixed rush our driving in my 1996 Mazda Protege. While my results are not fabulous, they are pretty good considering the vehicle has 150K on it.
Larry
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mobile_army_sugical_hospital 11:56AM (3/30/2007)
Hey, I've been doing this for the past year or so with my 96'Metro (3 cyl). I went from 42MPG to a consistent 46.5+. The key is to coast, shut the ignition off long before you even come to the red light. Like Larry says above, bump start it if you can while still coasting. About 20% of the time I can time it so the light turns green as I coast up to it and bump it back. A thing of beauty!
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MikeW 12:35AM (4/01/2007)
The time for a modern direct injected gasoline engine is 0 seconds.
Modern indirect fuel injection, sequential multipoint-or port is you so desire (on a warmed up car) is 1 second
The carburetors are dead and buried. (set choke, engage fast idle cam) even those it wasn't as bad as people made it out to be.
If a starter is rated at 2,000 watts and only runs 0.5 second to refire a warmed up engine. 1 KW-second isn't much juice. Would it take all of 10 seconds for the battery to be recharged by the alternator?
High current contact erosion could be a problem, more wear comes from cold starts. (only if your car is a chrysler, those bastard bean counters used extra thin contacts, can you tell I had one fail), the flicka-flicka of the key trick only works for so long ~3-4 months.
The idea is when two parts that are non or marginally conductive meet, you release the solenoid, (let the key go), then immediate re-turn the key to start. A conductive pathway may be formed, and the starter will rotate and the engine should fire.
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MikeW 1:08AM (4/01/2007)
This had small merit in the carburetor days, but is completely bunk today.
Cranking a warmed up engine uses less fuel compared to the fuel burned at idle. Sure the programming is for the revs to rise and come down, so call it a draw.
Engage starter (a whopping 2,000 rating) for all of 0.5 seconds (starters do still have overruning clutches?), it might take all of 10 seconds for the alternator to return that energy to the battery.
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