Quote:
Originally Posted by ChipB
I think this is a bit over-stated. Yes, there's extra wear, no doubt. But all the engine oil doesn't instantaneosuly drain when the pump stops - it takes several minutes for oil film to dissipate. And since the oil is warm, pressure builds almost immediately when the engine restarts. As for extra wear on the starter motor - sure, but the engine is warm and well oiled (at least compared to a cold start) and the RPMs for restart are very low, so the work required from the starter motor is quite low. Generally electric motors fail due to a combination of age, corrosion, and the stress of having to do heavy work, not so much from duty cycles themselves. I would guess that the wear on the restart is probably 1/10 of cold start wear. You factor X is therefore more like 2 than 10. I owned my last two BMWs for 12 years and 11 years respectively, and never had to replace a starter motor even though they were daily drivers. So the trade off is the potential extra cost of a replacement starter motor that this vehicle may need that it otherwise wouldn't have, versus gas savings.
I will say that it takes getting used to. I find if I don't pay attention at the stop light and suddenly realize that the light has turned green and try to accelerate quickly it's a pain in the butt. The practice I've adopted is watch the lights, and when the cross-street's light turns yellow a slight lift of pressure from the brake pedal - not enough to cause the vehicle to roll forward - is enough to start the motor so that it's ready 3 seconds later when the light turns green. On the other hand my wife hates it and always turns the feature off.
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If you don't like it why not just turn it off? Undoubtedly it is there so the 'tests' for MPG & CO2 shows a higher MPG and a lower CO2 figure. The plug in hybrid X5 should be interesting next year with instant torque from the electric motor so no lag at take off.