So i went to the mountains this weekend and got 15 mpg going up and 25 mpg on the way down, but on the way down i would shift into neutral for about 10 or 15 minute intervals until there was uphill. The RPM's would drop from about 2500 to around 600 My question is, is this bad for your transmission? I have an automatic transmission

bump

You are missing out on compression braking by shifting into neutral. When you are going downhill you will burn up your brakes. I'm thinking its not a good idea to coast in neutral for that long with an auto, but I'm not entirely sure. The thought never crossed my mind before.

yeah you will use alot more of your brake pads....

Being in neutral itself will not hurt anything except brake pads, as mentioned above, but most modern vehicles shut off the fuel supply when coasting in gear, so by shifting into neutral you might also be using more fuel than just coasting in gear.

It's lose lose.

It wont hurt the trans at all but will burn up your pads.

Keep it in gear. It's safer that way.

Where you can damage the tranny is by shutting down the engine while coasting, with no fluid circulating bad things will eventually happen. Of course, coasting in neutral with the engine off is just asking to die in a fire as well.

The costly thing here in the States is it is illegal to coast on the road and the fines for it are steep and usually also get you a Careless driving ticket as well.
It is just not worth the mileage you think you are gaining!
And most fuel injected cars shut down fuel while coasting, which is why they get better mileage than a carburated car in the first place.
Itsme

And the cops would know that you are neutral... how exactly?

With the engine running, the pump for the trans is still spinning, so pressure is still there. No problem at all with shifting into neutral.

Engines don't cut all the fuel and the fuel that's still in there is more than at idle. Check your injector pulse width and fuel pressure, it's more than at idle with closed throttle position switch 'On' and rpm over 1k. Although you give up compression braking, you're using less fuel. But the trade off is brake wear.

Going down the major passes here in Colorado (Vail Pass and Eisenhower Pass), I just kick it out of overdrive and it stays at or below the speed limit. I get close to 90k miles out of my brakes. I also service my transmission every 60k miles with a positive displacement machine using BG products.

You can save fuel or you can save brakes, but you can't save both!

Cyclemut, They don't often catch coasters, but usually they do when somone is going downhill at high rate of speed and is not using their brakes much.
You are right, you are still burning fuel when going downhill, but you are getting like 100 mpg during that time. It is the uphills that kill mileage!
It just comes down to the better choice for you. I choose not to coast and I have a manual in both of my trucks. The diesel truck I have has an exhaust brake and that is a lifesaver, when towing my hefty toyhauler downhill!
http://i616.photobucket.com/albums/tt243/ItsmeWayne/100_0100.jpg

Holy freakin' sweat toy hauler Batman! Now that's what I'm talking about!

I'm not saying anyone will get 100mpg in their rig doing this, but was more simply answering his direct question about hurting the trans and dispelling the computer shutting all the fuel off thing. Nissan is concerned (I believe, overly concerned) about these engines running lean so they'll run 'em rich whenever possible. A high rev, no throttle condition can tend to overlheat the cylinders, yada yada.

Nice Cummins Itsme! I love those engines, just hate the electrical systems that come with the rest of truck. Me and Dodges don't combine well for some odd reason. It's weird.

Am I the only one then that coasts when appropriate, and is in gear otherwise?

Like shifting, I just pick what seems right at the time.

If its a steep hill and I don't want to be going too fast, I am in whatever gear keeps me at a reasonable speed.

If its a mild enough slope where I don't need gas, but my brick-like aerodynamics will keep me from going too fast, I'll coast.

It sort of SOUNDS like the rest of you ONLY do one or the other?


It almost sounds like "Who here uses their brakes?"

"I never do, it makes me go too slow or stop, and wastes gas"

and

"I always drive with my brakes on, its better to waste gas than to die in a high speed accident"

etc.


:wink-big:

I do both, that is to say, I go both ways. ;)

Am I the only one that goes downhill like a slalom skier to both save gas & brakes at the expense of my tires? :)

Am I the only one that goes downhill like a slalom skier to both save gas & brakes at the expense of my tires? :)

LOL

My tires are more expensive than my brakes....plus, I always worry about a kid or a dog, etc, running out into the street.

I hit too many Jersey and PA deer as it is....so, I don't tend to drive THAT fast...the whole physics thing is sort of a limiting factor when I start doing the force = mass times acceleration thing....and limit my speed to #'s that seem more survivable.

:wink-big:

I do both, that is to say, I go both ways. ;)

LOL

So, you and I both go both ways...


but never together....



:2cool:

No sword touching!

The costly thing here in the States is it is illegal to coast on the road and the fines for it are steep and usually also get you a Careless driving ticket as well.
It is just not worth the mileage you think you are gaining!
And most fuel injected cars shut down fuel while coasting, which is why they get better mileage than a carburated car in the first place.
Itsme

whether this is true or not is not relevant. the important thing here is that this is the funniest f'ing thing ive ever heard.