Just curious...I figure I would save gas by putting the gear in Neutral when i'm going down a hill on the highway and when I drop below a certain speed, I would put the gear back into Drive. Is that a bad thing to do?

I.e. car traveling at 90 mph, I would put it in Neutral to coast down hill, and when the speed drops to about 65, I would put it back in gear, then repeat the same process when I'm able to coast.

Weird how when I took a 1500 mile road trip, I only averaged about 25 mpg on the highway going 75 with the a/c off.

Anyone have any feedbacks?

 

Actually you would probably use more gas that way , Basically in gear in decell conditon foot off gas trans braking the car would be in fuel cut ( no fuel being deliverd . If you put it in N the car would be idleing and using fuel

 

I've always thought that more fuel = higher rpms. So when the car is at 3500 rpms, it would be using more fuel then it is at 900 rpms?

 

You would get better gas milage by just driving at 65mph.

 

but then you're going to put extra load on the engine when accelerating back up to 90 so you're not going to save gas.

it's better to maintain one speed (rpm) than go up and down.... and even if it did save you a few cents per tank, the first ticket you got for going 90mph would wipe out all the savings.

 

Fuel injection only uses fuel when needed . In decel basically the fuel is cut no matter the rpm .

 

I would think you could cause transmission damage by going that fast with the transmission pump only pumping at idle speed. The engine rpms should be matched to the wheel speed for all of the drivetrain to work as designed. It may not be as big a deal with a manual tranny because it does not have a pump and hydraulics. Just seems like a possibility to me. I would not recommend doing it.

 

Not one the 2k3 auto. I get the best gas milage going 40-50 and 75-85. Everything not mentioned gives the lowest gas milage.

 

Wouldnt that be messin up the internals of the transmission, clutchbands and stuff? From forcin it in and out of gear while goin pretty fast

 

I hear what you're saying, and maybe that would apply to some older cars, but the beauty of the Maxima is that when you're coasting downhill in gear, even though RPMs are higher, no fuel is being delivered at ALL (therefore during deceleration/coasting, higher RPMs have no effect on fuel consumption during that period)
On the other hand, it should add engine braking to the mix, so if the car slows down noticeably without touching the accelerator then it may not be as efficient (since idling in N would let you accelerate thanks to gravity)

As for tranny wear, I'm sure it would do something over a long period of time, but then I drove an old '90 Mazda 626 automatic for ~30-40K miles (it had 186K when I was finished) and I used to coast in neutral, manually shifting up/down too (it had the HOLD system, basically mazda's old manual-shift automatic) and it never showed any signs of mechanical failure as a result (it slipped occasionally when really cold, but it did that even when I first got it)

 

just leave it in D. you get worse mileage puttin it in neutral and you put more stress on the tranny. It is perfectly happy coasting in gear and by shifting it out of gear then back in, that creates friction = more wear

 

i asked this same question a while back
someone replied that 'N' acts like a gear just like all the others and its not a good idea to be going too fast, just like you wouldnt speed up to 60 and drop it into '1'......thats what i got......gas is a whole other issue

 

Can i apply a few tubes of ky jelly? Ya think that would help?

 

There should NOT be any issues when coasting in neutral on an automatic transmission. Actually, the engine can benefit from lesser wear because of lower engine's RMP operation. The only thing that can possibly damage the auto-trans is when you shift it back to gear while at higher cruising speed (this I had confirmed w/the experts). As for fuel saving benefits, I am going to investigate on this matter, technically.

 

Well? I'm waiting...lol j/k

 

Is it ok to throw your car into while sitting at a red light waiting for the to change? I do this all the time, and I just wanted to know if this could/would cause any problems with the transmission, because if it does, I'll stop doing it.

 

I do it too. I was told by my mechanic while stationing for long period of time in "D" mode...to always shift the trans into neutral.

 

Auto transmission-101
http://www.familycar.com/transmission.htm

Try post your question here:
http://www.2carpros.com/topics/trans.htm

 

you are an idiot.
you will spend the extra .000003 cents ur "saving", ur actually using more gas...paying for a new tranny once ur warranty is up. You want gas milege? Buy a manual!

 

uhh..mechanics do what kind of business? They are worse then lawyers...of coarse he'll tell u that! so u go back to him when u need a new tranny.
People's trannies are taking craps left and right for no reason. Heath, NT2SHBBY
was slippin at 11k. giovanni, kloogy at 59k, no reason...

Treat ur tranny like u would ur girl... unless....ur some phycho beater

 

Keeping your transmission (auto) in gear while sitting in hot weather may lead to it heating up quite a bit, so that's why it's better to put it in park or neutral.

Auto transmissions are not harmed by putting them out of gear, it's the putting them back in gear at speed bad since you force the transmission to synch up to engine speed very quickly.

That said, it makes absolutely no sense to coast from 90 to 65 and then back up.

It makes sense to coast down from like 60 to 0 and then when you stop for the light/ralroad/turn/sign/whatever put it back in drive and be on your merry way.

 

Treat ur tranny like u would ur girl... unless....ur some phycho beater[/QUOTE]

Funny that you quoted this phrase and mentioned some of the members (not pointing names) who obviously are into enthusiastic driving and PROBABLY had taking their vehicle over the limit!

FYI: The mechanic happens to be my best friend's brother who had more than 15 years of working experiences.

 

lol, o, something new
Well shifting into N isnt bad...its shifting back while ur driving...

 

I've found that my MPG starts to decline over 70 MPH. Cruising @ 90 will use more gas than crusing at 70. I average about 27.7mpg @ 70 MPH. That will pull back to mid 20s over 70.

On all fuel injected cars with OBDII computers, (that's about 100% of cars made today), the computer will stop pulsing the injectors (cut fuel) when certain conidtions are met by the MAF, manifold pressure, and throttle position sensor reads closed but the RPMs are over a certain threshold (extended deceleration).

This is done to to reduce emissions and aid in engine braking.

I can see your point about putting it in neutral going downhill. Personally, I think that may actally use less gas since you're letting gravity pull the car along. Leaving it in gear you would actually have to give it some gas to not decel too much from engine braking. But, it's such a small amout it's not worth the risk and wear of putting the trans back in D at such a high speed. That is harsh on certain clutches in the trans.

 

My experiences exactly. 70 mph is about optimum for my car. Anything over 70 and mpg starts to drop, and fast. 80 gets me about 24.5mpg. I'm talking manually calculated mpg, not what the little trip computer says.

 

is one or two extra miles per gallon really worth the chance? If gas is that big a deal for you just get a Prius.