Again, I was skeptical when he first told me about this, but once more, I wasn’t sure if this was really true or not. So, I decided to research and find out if it would really make a difference if one puts a car with an ‘automatic’ transmission on neutral at the lights. Oh and by the way, I don’t really think that you can save gas by putting your engine on neutral at the lights.. mainly because your engine will pretty much just idle and while it’s idling it’ll still sip some gas – so I doubt if there will be any gas savings. For gas savings, I’d try turning off the engine when possible (not at intersections though.. because that’s just be too little time to gain any measurable savings), and perhaps use cruise control when possible, and get rid of any extra weight in your car. I guess if you really wanted to save gas, you could try hypermiling (or may be hyperkilometering if you’re Canadian).
Ok, so the question here remains that would engine life/transmission life really be better if you keep you engine on neutral. In my opinion, I don’t think it makes a difference for 2 reasons:
1. The engine is still on if you keep the gear on neutral. This means that you won’t really be saving any ware and tare in the engine by putting the gear on neutral – so I don’t see how you can improve the engine life.
2. Shifting back and forth might actually put more ware on the transmission, because you’ll constantly have to shift in and out of gear every time you are at an intersection (which is a lot of times, considering the amount of times I always have to stop at an intersection)
Furthermore, I think that on an automatic car, neutral is pretty much the same as stopped. Although, I guess if you’re in neutral, you don’t really have to step on the brakes because the car won’t really move forward as the engine is disengaged from the transmission. Therefore, you can probably save some money with the brake lights, the brake pads, and perhaps break fluid, but I don’t think it’ll make much of a difference if you’re driving a car with an automatic transmission.
Anybody have any other ideas/thoughts on this issue?
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Wrong on both counts.
ReplyDeleteEveryone seems to agree a manual transmission follows the rules, so I won't have to dispel a basic misunderstanding of physics for the manual transmission.
For the automatic transmission:
1. Neutral is NOT the same as being in gear when stopped. Let me explain the work / mass / energy equation this way:
Hook yourself up to a very heavy cart, with no wheels. Begin dragging this cart down your street, then stop at a "red light".
Now, instead of pulling your tension off the load straps to wait for the light to change, KEEP the tension on them, to the point that someone must stand in front of you to keep you from surging forward.
Not only are YOU doing more work, the person holding you (your brakes!) is doing more work.
Now it is true that the engine & transmission (your muscles & joints) will receive a bit of a bump as you put your energy back in to the straps to continue on, but both (a) the basic physics equations and (b) your body will agree that there is MUCH less overall exertion on all fronts when you ease back off the straps at the "red light".
Finally, if you are skeptical your car does not follow the rules of physics, test this and my next point on your next 2 tanks of gas.
2. Coasting USES LESS FUEL.
(a) This is VERY easy to verify by comparing 2 tanks of gas. You will see a marked difference. Period.
NOTE: You should not coast on very steep or long hills that would require constant braking. The simple rule will always hold true that coasting uses less fuel, but besides the added danger of too steep/long a hill in coasting, you WILL end up with excessive brake wear by constantly braking on a downhill.
(b) Your engine's "braking" principle USES TORQUE. 1.5k idling RPM is NOT the same as 1.5k RPM under load. The best way to explain this is to refer back to the physics work equation and the factor of 'q' (torque) in the equation.
I don't know if this will translate easily, but think of helicopter. If you're not familiar with the "Ellehammer" Principle, just remember when you've seen a helicopter with the blades turning at full speed on the ground. The RPM's are the same as if it was in flight, but much less work is being performed. Notice that when it takes off, the blades don't speed up, it just takes off. If you could see each blade coming past you, you would see the pitch of the blades changed as the "grab" the air instead of spinning flatly through it, thus causing the torque, or work, increased fuel consumption and, thanks to the Ellehammer Principle, the aircraft to leave the ground.
Now, w/o describing the whole thing, if you can just accept that the blades are turning at RPM (x) when sitting firmly on the ground, and still at RPM (x) while taking off (and eating the MOST fuel). If you were inside the cockpit, you would actually see the Nr (AKA RPM AKA rotor speed) drop slightly, then return, as the rotor head takes on the work.
The RPM is the same, yet MUCH more work (q) is being done, and MUCH more fuel is being used.
An engine (whether your body, a car or a helicopter) under torque is doing more work, the RPM is not the sole factor. Your transmission is also doing more work in this situation.
In a situation where you can consistently & safely coast down a long decline(s) with minimal application of the brakes, you will ALWAYS see greater fuel economy, just as you will ALWAYS see greater fuel economy by disengaging the transmission and coasting gradually up to a red light or other necessary stop when you can see it far in advance.
You will see you can mitigate any "neutral drops" by reengaging the transmission at the "sweet spot". If you surf, you know what I mean. If not, you can learn to feel it first by reengaging the transmission at the precise speed at which you disengaged it. Once you get the hang of that, you'll start to feel the "sweet spot".