I know all the secrets to extending gas mileage. What harm is there is putting the care in neutral while waiting for a traffic light. I know you do not recommend doing it while coasting, but does it do any harm to the automatic transmission?
With an automatic I see no or very little increase in MPG by shifting to “N” while at a traffic light. I think that it will only wear the transmission (a very little bit if at all) I’d leave it in “D” and drive with a lighter foot. What secrets are you talking about anyway . . . I think that sharing some of those secrets might help others who read these posts. Rocketman
It does absolutely no harm to shift into neutral when stopped. Some folks might challenge this statement, but they have no evidence at all to back them up. So do as you see fit. Incidentally, neither method has any effect on your gas mileage. None.
It won’t harm the transmission, but it won’t save any gas, either. I suggest leaving an automatic in gear at traffic lights. There is no advantage in shifting to neutral, and it could be a safety hazard. If you need to move quickly you won’t be able to.
Do NOT, under any circumstances, shift to neutral and coast while driving. NEVER.
WHY??? While coasting, does lower revs save gas, and it provides a longer coast with the engine is disengaged.
Coach, your method may have been true for older, carburreted cars. It no longer applies to modern fuel-injected computer-controlled vehicles. They all have a gadget called the throttle position sensor (TPS). When you coast, in gear or not, the computer knows to shut down the gas flow so it is merely enough to maintain idle. The rpms hardly matter.
If you still believe there is a fuel savings, do the calculations. Or check with the math coach. You may come up with a penny per mile. Your sense of due economy is commendable, but some cost-cutting techniques simply do not yield measurable results.
While I agree that on modern cars it saves little to none, I don’t see how keeping the car in neutral is a safety hazard. Lots of us have manual transmission vehicles and put it out of gear when we are at a stop light. How would that be any different?
Now if you are at a light that you know to be exceedingly long, or stopped at a RR crossing, by all means shut the car off for the duration.
The problem with shifting into neutral and then back into gear at every light is that this allows fluid pressure to slam those clutch plates together. That very faint, subtle bump you feel is actually a sledgehammer at work.
IMHO, it’s unneccsary and harmful to the transmission.
And, in fact, most cars these days will completely shut off the fuel when coasting in gear, wheras if you shift into neutral it has to use a little bit of fuel to keep the engine idling. Theoretically, coasting in neutral will actually use more gas!
Agree with you OK . . . and let me add that the modern automatic transmission is really complicated and expensive to fix, and not intended to be shifted in and out of gear at stop lights. One other thing for the OP . . . if you forget to shift back into “D” and drift backwards (I know, manual tranny drivers could do this also) you’ll hit whatever is behind you . . . and I believe that you might be more likely to do this than manual tranny drivers simply because you are used to driving an automatic. Just my two cents. Rocketman
When coasting in neutral the car is not being slowed by the engine there for getting more miles (inches) for the energy that got you to the speed at which you started your coast.
It’s not theoretical. In a modern car, you will use more gas coasting in neutral, than running downhill in gear with the throttle closed.
If you have an instantaneous mileage function on your trip computer, you can see it happen. Mine gets about 40 mpg coasting in neutral versus up to 99 mpg running downhill with my foot off the gas pedal.
I agree on transmission prices. Back in the old days one could get a rebuilt transmission for 250 bucks exchange but with high tech engineering and electronics the price of a transmission can be a car killer when the vehicle has aged a bit and accumulated some miles on it.
Going back about 20 years I can remember very well listening to several Subaru owners going ballistic over prematurely failed automatic transmissions which were almost 5 grand at the time. Add sales tax and it’s in excess of 5 grand.
They just knew they were being ripped off by us but the dealer COST on those transmissions was slightly over 3700 dollars.
The first time I worked up an estimate on one of those it caused my heart to skip a number of beats also. The sad part was that the transmission failures were not related in any way whatsover to the car owners driving habits or lack of maintenance.
If it was my car and someone hit me up with an estimate like that I’d go into the stratosphere also.
Is 0.001 mpg worth it?
Kinda makes you think twice about the “rocking” procedure many people employ when stuck in snow dosen’t it? “R” to “D” repeatedly until you get unstuck? Holy cow! Think I’ll stick with a manual shift. Rocketman
Automatic transmissions shift gears hundreds of times during a typical trip, shift in and out of N at the red lights and now it has to make hundreds of shifts per trip plus a half dozen more. Unless you do something really bone-headed like reving the engine and dropping it into D to burn rubber, I don’t see the harm.