Zythaxus

putting the automatic transmission in neutral with the engine running disengages the geartrain, like depressing the clutch pedal on a manual transmission. - note that with modern automatic transmissions, the engine must be running to keep the transmission fluid circulating; which lubricates the geartrain.*
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however, my state and probably many others, prohibit the practice of coasting down hills with the transmission in neutral.* the logic behind this is that first, the engine helps with braking on downgrades, and reduces heat and wear in the brakes.* second, if the transmission is disengaged, then the transmission will have to be reengaged before the driver can accelerate to avoid trouble.

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