Turning off engine with an automatic - Fuel Economy, Hypermiling, EcoModding News and Forum

saunders1313 · 10-11-2008, 01:32 PM

I've heard some posts saying that you shouldn't turn off the engine while coasting if you have an automatic. The only reason that I've found for this is that the transmission pump turns off. Are there any problems that could arise from turning off the engine? I P&G a lot and I'd like to start turning off the engine during long glides.

aerohead · 10-11-2008, 01:54 PM

My thought is that without the engine on (and pump operating as you mention ),it's the same as towing an automatic transmission car with it's drive wheels on the ground,which usually burns up the transmission.

trikkonceptz · 10-11-2008, 04:08 PM

While the claims of damaging automatic transmission that are flat towed in neutral are true. This damage can occur over hundreds of miles consistently being towed in N. I EOC "Off" coast my automatic with no problems. My longest EOC is 1 mile and I do it every day. I have been doing so for the past 20K miles with no ill effect. Before doing it though I did flush my tranny and added synthetic transmission fluid, just in case ... LOL

Cd · 10-11-2008, 06:35 PM

I tried this with my Civic once. The car has to be in park to restart the car, so I had to pull over by the side of the road.

Anyone know how to get around this ?

Cd · 10-11-2008, 06:41 PM

I shift into Neutral several times on my 7 mile commute to work. I coast down a hill for around 3/4 of a mile ( google maps ).

I find that even when I am going down hill, shifting into N will allow the car to go from 45 at the top of the hill to around 56 MPH at the bottom of the hill.
When I leave the car in Drive, it actually seems to slow the car.
I'll verify this the next time I go into work.

I know for certain that placing the car in N on level ground will allow me to coast at least 175 - 200 yards farther than leaving it in Drive.

( Is there a problem with my transmission ? )

Sean T. · 10-11-2008, 08:16 PM

In my car, going down a hill with a steady grade, I can shift into neutral and it feels like i tapped the gas. On one car, as soon as I shift into neutral it goes from 50 to 55, and I start gaining on the cars ahead of me.

I was actually about 5-10 car lengths behind a ranger the other day when I shifted into neutral and I had to use the brakes just before the bottom of the hill because I was gaining on him so fast... he never used the brakes once.

ankit · 10-11-2008, 10:17 PM

http://ecomodder.com/forum/showthrea...anny-1153.html

Some good points in this thread and the link posted above. I looked up my vehicle in a link posted in taht thread (ability to flat towing, which can be done in my altima). Now I do a daily ~.7 mile EOC, which is about 1/10th of my daily commute. Pretty nice IMO.

Z man · 10-12-2008, 02:34 AM

Quote:

Originally Posted by Cd

I shift into Neutral several times on my 7 mile commute to work. I coast down a hill for around 3/4 of a mile ( google maps ).

I find that even when I am going down hill, shifting into N will allow the car to go from 45 at the top of the hill to around 56 MPH at the bottom of the hill.
When I leave the car in Drive, it actually seems to slow the car.
I'll verify this the next time I go into work.

I know for certain that placing the car in N on level ground will allow me to coast at least 175 - 200 yards farther than leaving it in Drive.

( Is there a problem with my transmission ? )

No, you are right.

the transmission holds you back when coasting.

Neutral is better!

saunders1313 · 10-12-2008, 07:49 AM

Neutral is certainly better than just taking your foot off the gas. So as long as your car is supposed to be able to be towed flat it's ok to turn off the engine, but if it's supposed to be raised then it might cause problems. What about an ignition kill switch, would that get around the problem of not being able to flat tow the car?

TestDrive · 10-12-2008, 08:56 AM

Quote:

Originally Posted by saunders1313

What about an ignition kill switch, would that get around the problem of not being able to flat tow the car?

No. An ignition kill switch does nothing to address the problems some vehicle have with flat tow.

When you flat tow, the turning of the drive wheels turns some of the internals of the transmission. If the design of the transmission is such that the transmission fluid is pumped through the system in the same manner as when the engine drives the transmission, then everything is A-OK. If the design of the transmission is such that the transmission fluid is NOT pumped through the system in the same manner as when the engine drives the transmission, then parts of the transmission are subject to overheating - potentially leading to premature failure - particularly if you flat tow the vehicle for a significant distance.