Auto in N question
 

The family and I went to see my Brother in NC this past weekend
We took the PT Crusier - auto tranny.
I did hook up the SG so i could see how we did.
I gathered data on the car at several speeds to get a feel for the impact MPH on MPG

While doing this - i also wanted to see if coasting in gear was better or worse then costing in Neutral.

From a consumptiuon point of view - coasting in N seemed to use slightly LESS fuel than coasting in gear. I suspect the PT does not have a fuel shut off as the MPG did not skyrocket.
Both cases had the instant MPG jump to about 75 ( N hit 80 a few times) hence i called it SLIGHTLY less fuel.

I wanna play with it some more and get more data - a little more contolled than "30 minutes of data crusing across SC)

Here is my observation and question.

When i shift the tranny into N - I expected the RPM to drop to Idle - which is what the Manual in my Altima does... but it did not?

going 65 mph was about 2400 rpm or so. shift to N - engine stayed near 2400 RPM ! HUH? Both the TACH and the SG said this..

the MPG did go up so i know less fuel is going IN -
Is this normal for an AUTO? Am i thinking "Manual Tranny" here?

I do not drive the Crusier much ( wifes car) so i had not played with it before. but am a little confused at this.

Steve

Wow, that is interesting. I can only speak from my own experiences with the Scion XA (automatic) and when I go to N from 45 (since that's where I usually drive at) my RPMs take a dive from 1800-1900 down to 700-900. MPG gains are immediate (instant and current trip) but I'm trying to get into the habit of DFCO coast first then N-coast once I'm below the minimum 1200-1400 rpm to make the most out of fuel consumption.

it may be an idle controler problem

mine drops to idle also.
what happens if you rev the engine a little? it might not be totaly out of gear.

What is the idle after it has warmed up?

My wifes 02 Taurus does that as well....it seems as if speed and RPMs are in direct corelation with each other.
The more I slow down, the RPMS drop......

My Jeep Cherokee works the same way. Makes the N coasting basically worthless on the Jeep. especially since it has the fuel cut off. The only difference I see is I can coast just a little bit farther. The only time I use N is when I'm sitting at a light. Drops the fuel use from 0.74gph to 0.60gph.

Within a couple seconds mine drops to 800-1000 rpm when going to N at any speed. Dont have my mpguino done yet but Im sure Im using less fuel in N as well.

Next time i am in it i will check a few things.
warmed up idle ( Stoped in D)
warmed up idle ( Stoped in N)
Coasting in gear ( at some MPH)
Coasting in N ( at same MPH)

i will check the GPH and the RPM at those cases.
with that info I will hit the Crusier forums and see if this is common or an error

thanks for the inputs

steve

A lot of this depends on the gear and control layout of the transmission.
Because there potentiall could be a big difference between the engine speed (low)and the trans output speed (high), and what gear range is selected from neutral to re-engagement.
Some control strategies will hold the engine above idle in a neutral coast to reduce trans load on re-engagement.