Quote:
Originally Posted by SentraSE-R
The automotive pundits say 7 seconds is the magic number with modern fuel-injected cars... You'll use less gas to restart it than you'd waste idling.
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Quote:
Originally Posted by SentraSE-R
The 7 second comparison is strictly fuel used. It doesn't consider electricity to crank the starter. Bump starting is more efficient than using the starter, but you may pay by replacing your clutch sooner.
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Unless it considers the fuel cost of the cranking electricity then it's not a comparison at all.
The wear and tear issue of frequent cold starts doesn't really come into play with EOC because the engine doesn't cool down much. In the winter I shut off the blower fan to keep the coolant temp up, but none of my EOCs are long enough to drop the temps below the operating range even if I had the heat blasting.
I don't consider the wear on the clutch at all because you either excessively wear it or you don't. A good bump start is easier on the clutch than even the best standing start- you're using the clutch to move a few pounds of well lubricated engine innards just enough for the ECM to throw a spark at them. From a stop, you're using the clutch to move a whole car with a bunch of rolling and environmental resistance. If you can do that well, then the clutch will never notice that you now bump start. If you can't bump start well, then it's probably your regular driving that's killing the clutch and the bump starting is going to get the blame because you started doing it at around the same time you started paying attention. At that point your efficiency/value question should be whether you're better off with your own sloppy clutch work or an automatic's sloppy clutch work. You probably are- swapping a clutch costs a lot less than overhauling an automatic.