Some A/T questions

[Chalupa102]

Kind of a silly question, but for an automatic transmission, why can't you start a car while in drive? Anyone maybe shed some light why this is. When starting the car back up at a stop light, is it ok to go right from neutral to drive the moment the engine is started, or do you need to wait a few seconds? Do you need to wait a few seconds before accelerating after switching to drive? Also, is it good or bad to downshift, so to say, with an A/T to use fuel cutoff and minimize brake usage? For example, if your coming to a stop sign and you take overdrive off, which begins fuel cutoff, then after slowing down more (<25mph), put it in 2nd to maintain fuel cutoff still slowing the car, and using the brakes to stop.

[thatguitarguy]

You can't start a car in drive because there is a switch in the trans or the linkage that prevents you from doing this. You can start the car, and immediately hit the accelerator even before you shift into drive, but this is abusive and not a good idea. The key to ecodriving is being smooth.

I do manually downshift to maintain fuel cutoff and don't think I'm causing any harm.

[Christ]

You can't start the car in gear for 2 reasons:

1 - It's dangerous. The engine could rev unexpectedly after/during starting, and cause the vehicle to move.

2 - The engine is already a huge load for the starter. Add in the transmission and fluid pump... pumping fluid, and you've got even more load. All the while, it's trying to move the car, perpetrating #1.

You could bypass the Neutral Start Switch, but I don't recommend it.

BTW - Park is just Neutral with a locking pin.

There is nothing wrong with downshifting in an automatic. In fact, it's recommended to save engine/transmission wear and brake linings. If you're going down a grade, or slowing down, downshifting works exactly the same as it does in a manual. You don't always need to use your brakes to slow, often, you can move to the next lowest gear, ready your brakes, and use engine compression to slow the vehicle to an appropriate speed for the situation you're negotiating.

If you find that your transmission is shifting up and down frequently, such as in hilly terrain, it's best to shift manually into the next lowest gear, or slow down to prevent it. Each shift represents clutch wear and fluid shear, which creates heat. Often, worn parts aren't the cause of a transmission failure, instead, it's bad/burnt/overworked fluid which allows other parts to self-destruct.

[Chalupa102]

Thanks for the replies. I've been downshifting for about a week now and just wanted to make sure it wasn't bad.

Originally Posted by thatguitarguy

...You can start the car, and immediately hit the accelerator even before you shift into drive, but this is abusive and not a good idea...

I would never hit the accelerator before switching to drive. That just sounds like it would be horrible for the tranny.

What i was wondering with questions 2 and 3 was, say for a senario i'm stopped at a light with the engine off, tranny in neutral holding the brakes and the light turns green. I'm the first car in front and can't see the side light that turns red, so i start the car and immediately put it in drive, then about a second later let off the brakes and accelerate from the light. Am i good by putting it in D from N as soon as the engine is started, or do i need to wait a second before going to D?

I was asking about the starting in D question cuz one time before i forgot to switch to N and couldn't start while in D. Luckly no one was behind me at the time.

[thatguitarguy]

Just my opinion, but I think you're OK with shifting into D as soon as the engine is running in the situation you are talking about. Not OK for the first start when the engine is cold. Again the key is being smooth.

Even if you can't see the light on the other side, you should be able to read traffic and have a feel for how long they've had the light. As the light turns yellow the traffic flow should be slowing down and maybe people are getting ready to make their left hand turns and such. It's about paying attention to everything that's going on around you, and should be a part of every driver's routine. Defensive driving techniques go hand in hand with ecodriving techniques.

I'll turn off at a long light or a train crossing or construction delay, but I definitely don't turn off for every red light.

Look at the big picture.

[Christ]

Yes, you can put it in D just as soon as you let off the key and the engine is started. Gentle on the accelerator until you start moving, though.

If you've got a back road and some time, you can put a manual button on the starter solenoid and that will allow you to crank in any gear, so that you can see how your vehicle would react to being started in D or R or any other setting. It *shouldn't* damage the transmission, but it will work the starter a little harder. It may save you a gram or two of fuel on restarts while you're waiting for the transmission to engage back to D, etc.

[Thymeclock]

Originally Posted by Christ

Yes, you can put it in D just as soon as you let off the key and the engine is started. Gentle on the accelerator until you start moving, though.

True. I shift into neutral at virtually every red light I'm waiting at, then put it back into drive when the light changes. Why? because it takes a load off the A/T, and thus it generates less heat.

But I don't understand why you are downshifting an automatic. I can understand how it will provide braking (and save your brakes to some small degree) but how will it save gas? If the downshifted engine is braking the car more, it will be coasting less.

[Chalupa102]

Originally Posted by Thymeclock

But I don't understand why you are downshifting an automatic. I can understand how it will provide braking (and save your brakes to some small degree) but how will it save gas? If the downshifted engine is braking the car more, it will be coasting less.

I do use a lot of NICE-on coasting, especially to lights. The times i tend to downshift is when i have to come to a complete stop at the bottom of a hill, or if a light changes unexpectedly and i have to slow down pretty quickly. With downshifting you should check your mirrors to make sure no one is tailgating you. I sometimes throw on the flashers for a second to let the person behind me know that i'm dropping speed. I will also use the brakes in conjunction with downshifting if there are cars behind. The thing i like about downshifting over NICE-on coasting is fuel cutoff (reading 9999 on sgII), but of course you do slow a lot faster than you would doing NICE-on coasting.

[Christ]

Originally Posted by Thymeclock

True. I shift into neutral at virtually every red light I'm waiting at, then put it back into drive when the light changes. Why? because it takes a load off the A/T, and thus it generates less heat.

But I don't understand why you are downshifting an automatic. I can understand how it will provide braking (and save your brakes to some small degree) but how will it save gas? If the downshifted engine is braking the car more, it will be coasting less.

There are times when you'll need to stop or slow faster than coasting in neutral would allow. It's the next best thing, especially if your vehicle has DFCO.

As far as normal driving, I downshift to provide engine braking on hills, and that's about it. If you're in hilly terrain, it's not to save fuel, it's to save your transmission. Each shift creates clutch wear and fluid shear which heats the transmission more, and that's bad, so you downshift to keep the transmission from shifting up and down all the time. It could also save fuel in some cases, because upshifting and downshifting are fairly inefficient, and being in a lower gear, even with higher RPMs/less load, you might still use less fuel in some cases.

[Thymeclock]

Originally Posted by Chalupa102

I do use a lot of NICE-on coasting, especially to lights.

What is "NICE-on"?