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Is it OK to switch between N and D on an automatic transmission doing free-wheeling and etc? Is that going to wear our the transmission?
In my Dad's later years he drove me crazy when he drove somewhere and I was a passenger. He was a farmer and drove many different kinds of vehicles for many years. He usually drove Chrysler products of the 60's and 70's in my lifetime.
Well, he retired from farming and treated himself to a new car for retirement, a 1990 or '91 Buick Park Ave.
So he would pull up to stoplights and when the light was red he would put the car in neutral. I told him over and over that the transmission was electronic, computer controlled. He could leave it in drive with the brake on until he runs out of gas and it won't hurt it a bit.
Then the light would turn green and it would take the 80 something old man a few seconds to shift from N to D and the cars behind us would go nuts
...Well, he retired from farming and treated himself to a new car for retirement, a 1990 or '91 Buick Park Ave...
...So he would pull up to stoplights and when the light was red he would put the car in neutral. I told him over and over that the transmission was electronic, computer controlled...
Those Buicks seem to go quite slow in rural areas! (Instead of 55, 45.)
And my elderly dad would always turn everything off in the car so it would not use electricity when the car was off. I too tried explaining he did not have to do that - to no avail!
Most cars can (read: will) shut off fuel injectors entirely, when the throttle is closed and the RPM is over whatever threshold is set in the engine computer. When you are decelerating (manual or automatic) the engine continues to turn with no fuel until the speed of the engine slows and the injectors begin to cycle again. The engine doesn't "shut off"--the fuel does, temporarily. You don't feel this happen, because the engine computer is smart enough to restore fuel injection when it's required, and before it becomes obvious to the driver, that it was shut off in the first place. If you drive down the side of a mountain, fuel injectors may not fire at all for miles at a time, unless throttle is added or the engine speed falls.
When you intentionally put the car in neutral when coasting, the engine falls to idle, and must use fuel to prevent stalling. This can defeat the fuel shutoff that may otherwise be taking place if the transmission was left in gear.
Cars constantly recalculate many variables and attempt to maximize fuel economy. Basically, it's unlikely that you are doing yourself any favors by trying to use an ancient fuel saving strategy in a vehicle that is already working to save fuel every minute that you drive it.
If this is still too complicated, this video might give you an example that makes sense. Simple example of fuel shutoff (via calculated fuel flow figure) in action.
When there's no fuel, would the engine go off and re-ignite? It doesn't do that.
It does actually. There is still a link between your wheels and the flex plate/flywheel on the crankshaft via the transmission so it doesn't stop rotating.
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