Putting automatic trans in neutral when going downhill?

[Yarus Maximus]

There are stretches in my commute that are 1/2 mile downhill and rather steep. Is it safe to put the car in neutral, then back to drive at the bottom of the hill? I would like to save some fuel but do not want to harm the transmission.

[Astroman]

It's not safe or good for your transmission, and you're actually not saving as much fuel as you would leaving it in gear. While in gear and going downhill DFCO kicks in, shutting off the injectors. The engine is still running, its just not getting fuel. When you put it in into neutral DFCO doesn't work so you still are using gas. I have an automatic with a scangauge II.

[127.0.0.1]

Originally Posted by Astroman

It's not safe or good for your transmission, and you're actually not saving as much fuel as you would leaving it in gear. While in gear and going downhill DFCO kicks in, shutting off the injectors. The engine is still running, its just not getting fuel. When you put it in into neutral DFCO doesn't work so you still are using gas. I have an automatic with a scangauge II.

above....totally depends on the speed, and steepness of the hill

some hills, dfco is more economical
some other hills, neutral is more economical


you really need a real-time mpg reading if you need to nail it down.

if in doubt, leave it in gear...it is 'overall' better for the car and mileage

neutral doesn't hurt the auto tranny, but kicking it back at improper rpm's
can stress the solenoids and clutches. and with no engine braking you may
just end up wearing the brakes faster

[Astroman]

Yeah a Scangauge II or similar works best to know for sure. Where I live 95% of the hills work best fuel wise leaving it in gear.

[KrazyDawg]

There's a part of my commute where I go downhill for 2 miles. If I start the hill at 60 it still stays in 60 while using DFCO. I don't have a scangauge but I figure I would get better gas mileage than driving slower up the hill and speeding down the hill.