Coasting in neutral or with clutch down?

[alohaspirit]

thanks for clearing that up


the last question is about shifting back into drive while coasting in neutral

lets say doing 20 mph - 40 mph

[PaleMelanesian]

At 20-40 mph, I just shift to D, let it settle a moment, and go. RPM is low so there's little stress to the system.
Above that, I give a little gas to put the rpm where it will be after the shift, then shift, settle, and go. There's very little bump when you do this.

[Christ]

I just put it in gear, even at 55-60mph.

Fluid shear in the torque converter prevents the "shift shock" that you would expect. It's like turning a fluid-clutch-type cooling fan... The more power you apply to it, the more times it will turn over before the hub catches up. This results in more heat applied to the fluid, since shear causes heat to build up quickly, but it's less heat generated than just starting from a stop.

[jonEmetro]

Back to manual trans. real quick. I swapped in the tall 3.5-1 trans. in my metro and have little engine braking in 5th gear and speeds of under say 45mph. So this question is model/drivetrain specific.

[Christ]

Originally Posted by jonEmetro

Back to manual trans. real quick. I swapped in the tall 3.5-1 trans. in my metro and have little engine braking in 5th gear and speeds of under say 45mph. So this question is model/drivetrain specific.

If you have little engine braking, chances are that you're not in DFCO. DFCO never occurs within something like 500 RPM of the preset idle speed, as there is too much chance for false input and the engine stalling as a result.

You're still better off to coast in neutral than with the clutch down, except that in neutral, you may be breaking some law somewhere...

I've never personally had a throwout bearing explode on me, but I've seen what happens when they do... I bought a car for $200 because one exploded, and the clutch disk also exploded, leaving only a thin sheet of metal between the flywheel and pressure plate, and ceramic dust all over the place inside the bell housing.

[jonEmetro]

Yes, blown throw-out bearing is very loud! I am 100% sure I'm in DFCO cause when I get down to about 1000 rpm I feel a change in decel rate and my SG2 instant MPG changes from 9999 to around 100mpg. I'm tellin ya, tall gears are the way to go.

[Christ]

I made an incorrect assumption that you were closer to idle. Apparently, the 500 RPM thing isn't true either. That's not something I've tested, but something I've been told by "reputable" people.

Taller gears are definitely the way to go, but DFCO still doesn't usually hold a candle to Neutral Coasting, and it definitely doesn't hold anything against EOC.

[jonEmetro]

No doubt, Ive been workin on my EOC skills and slowly improving. But I believe thats a story for a different thread.

[alohaspirit]

Originally Posted by Christ

Taller gears are definitely the way to go, but DFCO still doesn't usually hold a candle to Neutral Coasting, and it definitely doesn't hold anything against EOC.

DFCO < Neutral Coasting < EOC


this is good to know

[PaleMelanesian]

Originally Posted by alohaspirit

DFCO < Neutral Coasting < EOC

I concur, with two exceptions:
1. You are forced to brake for an unexpected stop. You might as well DFCO and save fuel and brakes.
2. DFCO to control speed on a long downhill.