Coast in Neutral (Automatic transmission) OK?


#1

In Colorado, we coast in neutral for miles down grade on I-70, with occasional brief braking to avoid over speed limit.

Is this bad for a 2007 Toyota Corolla, 1999 Expedition, or other automatic transmission vehicles?

Thank you


#2

2005 Corolla. Why can’t we go back and edit out errors?


#3

Because they still haven’t fixed the interface.

Back on topic: In addition to the theoretical reduced vehicle control that comes with coasting in neutral, some drivetrains can be damaged. Check the owner’s manuals of the vehicles to see if there are any warnings about towing them with all four wheels on the ground and the transmission in neutral.


#4

I coast in overdrive down these very long gradual slopes. Do not recommend doing it in neutral.


#5

This method is illegal in many states but clearly it is unenforceable.

It ought to be harmless but what’s the point? You are not saving any measurable amount of fuel. The preferred method is simply to set cruise control and let the car maintain its speed. If you tend to overspeed, downshift one gear and cruise in that gear.


#6

I had some ignorant reply in here. Took it out.


#7

Dont know about your vehicles, but with my 02 Sonata I’d be wasting fuel by coasting in neutral.

Coast in gear & the injectors are shut off.

Coast in neutral & the injectors have to supply enough fuel to maintain an idle.


#8

Its just dangerous for your health if an emergent condition arises where you need power.

What is the point besides the placebo effect of thinking your saving fuel?


#9

Interesting! Wondered about that myself.
If coasting in DRIVE, is there truly no combustion in the cylinders?
Thank you.
WHY WAS I NOT NOTIFIED OF ANY REPLIES?


#10

Still illegal anywhere? Thought that went out years ago when braking systems improved and automatic transmissions became common.
I get MUCH better gas mileage than cruise control. But I place in cruise control on the plains. (Still, oit will apply extra fuel to maintain speed and sometimes even downshift to maintain speed. What a waste. So I disengage cruise control when coming to some grades.)
Descending, it is better to briefly wear brake pads a little than downshift and increasengine RPMs, wear on drive train and possibly increase fuel injections/minute.


#11

In short, don’t do it.

The tranny hydraulic pump is driven by the input shaft from the torque convertor. Therefore if the output shaft is spinning at 50mph and the engine is idling it won’t be delivering the required pressure to the tranny. It’s the same as running your engine at 3000rpm with an oil pump delivering 1000rpm of oil pressure. The result is increased wear, burnt tranny fluid and a premature visit to the tranny shop.

Plus it’s dangerous, vehicle dynamics are balanced around an on load system, when you unload that system - coasting in neutral, the vehicle is inherently unstable. Try a sharp turn in neutral sometime and you’ll get the idea.


#12

Ditto!

Back in the '50s, some cars would suffer automatic transmission damage if allowed to coast (or to be towed for more than a very short distance) because they lacked a rear pump in the transmission. An automatic transmission with just a front pump could not supply fluid to lubricate some parts of the transmission if the car was allowed to coast.

While transmission designs have changed significantly since then, it is still potentially damaging to the transmission to allow a vehicle to coast for any significant distance, not to mention the reduced control on curves, the inability to react rapidly to an emergency situation that requires instant acceleration, and the plain facts that it simply does not save gas and is illegal in many jurisdictions.

This is a really great example of being penny wise and dollar foolish.


#13

“WHY WAS I NOT NOTIFIED OF ANY REPLIES?”

Perhaps your secretary was taking an extended coffee break. It is very difficult to get good help nowadays.

;-))


#14

Yep, the other nice thing about cars equipped with a rear tranny pump is you could push start them.


#15

Well the concensus here seems to be that it doesn’t save any fuel, but I’m not sure who to believe, you guys, or the people who milk 48 or so mpg out of a non-hybrid Honda Accord AT.


#16

“I’m not sure who to believe, you guys, or the people who milk 48 or so mpg out of a non-hybrid Honda Accord AT.”

If you really believe those people, then I have a bridge connecting Manhattan and Brooklyn that I would like to sell to you. Just because someone CLAIMS that they are achieving 48 mpg on an AT Accord, that does not mean that they are being truthful.


#17

I think the consensus is it’s dangerous, bad for your transmission and most likely illegal. Were you to be involved in a collision while doing this I’d guess your insurance company might also have some comment.

Any fuel saving would be questionable anyway and certainly would be eliminated by transmission damage.


#18

I remember push-starting cars with automatic transmissions. I recall most cars had rear pumps in the auto trans up through the
early-to-mid 60’s.

Ironically we found out the hard way at the gas station I worked at that car makers stopped including a rear pump. We pushed a customer car for miles and miles with our garage truck and couldn’t figure out why the car wouldn’t start! Live and learn.

Back to the base topic, I agree with all the replies. Coasting in neutral is penny wise, pound foolish and dangerous.


#19

It depends on the car. Some (like mine) totally shut off all fuel deliver when the engine is turning faster than idle speed (950 rpm on mine) That is only true for FI cars and not all of them.


#20

95% of the fuel you can save by driving techniques, you can get without doing anything goofy like driving in neutral with an automatic transmission.