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I have fried who puts his automatic tranny in neutral whill coasting down long hills and says he saves a lot of gasoline that way. The engine is idling going down a hill at 60 plus mph for a mile or two. He does this every chance he has.
Is this bad for your AT????
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EJO now a 1993 944T 197K; ex '65 123S; ex '75 245; and ex '81 242GT; also 2001 Kia Sportage, Chrysler 2002 T&C and 2006 MINI Cooper
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posted by
someone claiming to be David Hunter
on
Fri Dec 28 01:13 CST 2007 [ RELATED]
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I doubt that he saves any measurable amount of gas. Fuel to injectors is shut of while de-accerating in any event. I guess it makes him feel good though.
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Not at all, I would say that your friend could save even more gas by shutting his car off going down the hill and that wouldn't hurt it either,
Modern fuel injection systems cut fuel off completely during deceleration. But there is power to be lost, and fuel to be saved by via the torque converter.
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Goatman
So you are telling me that I in my 944T with AW71 (no torque conv.) could coast for a long time?
He says he keeps engine running in order to keep fluid pumping in his AT as the drive shaft/plate/gear is still turning?
Comments?
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EJO now a 1993 944T 197K; ex '65 123S; ex '75 245; and ex '81 242GT; also 2001 Kia Sportage, Chrysler 2002 T&C and 2006 MINI Cooper
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Good Morning folks,
Regardless of any fuel savings to be realized or any mechanical wear and tear, there is a safety reason to not disengage the transmission.
There are three ways to avoid an impending collision; change course, slow down, or speed up. Those three elements are the only inputs into the system that the driver controls. Why would you willfully remove one-third of the ability to avoid a collision?
--
Mr. Shannon DeWolfe -- (I've taken to using Mr. because my name tends to mislead folks on the WWW. I am a 51 year old fat man ;-) -- KD5QBL
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Safety is the consideration, and I'd offer the premise that coasting affects two of the three factors, the ability to accelerate out of a problem and the braking effect of the engine compression. Braking effect makes an admittedly small contribution to stopping the car, but sometimes 10 or 15 feet at 60-70 MPH is the difference between a close call and a fatal accident.
Also, I wonder how much more frequently your acquaintance has to change brake pads.
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All automatic transmissions have torque converters, including your Aisin Warner. If you engage neutral you WILL coast further then if you didn't. Try it.
Cars are towed many miles with the engine off, and the rear wheels are still turning the driveshaft.
I don't think it would hurt it at all, as long as the tranny was full.
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It is my understanding that older AT's had two pumps, one driven off the output shaft, the other from the input shaft.
Now, I believe, they have only the front pump. Thus towing without the engine running for any significant distance will result in damage.
As to coasting, gas savings are iffy, but perhaps measurable. With the engine running, even at idle, the front pump is running and ATF circulating so there should be no damage.
The safety considerations are of most importance. It's a judgement call.
I, too, coast, but for other reasons. I have noticed that braking effect is better when approaching a stop. As from 30mph to zero. Then back to "D" while awaiting the green light.
Pass this to your friend.
Regards,
Bob
:>)
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Bob
I agree to what you said. I'm a manual shift driver and therefore like to shift my cars, but the Volvo and Chrysler are ATs.
Today with 4-6" of snow coming down here in West Michigan I too throw my Volvo in neutral while braking. It does make the car stop quiker at the lower speeds in this slippery stuff. While at a stoplight I always put her in neutral so I can keep the foot off the brake without lounging forward.
He doesn't coast in traffic, but most often on the highway while exiting with a stop at the end and therefore coasts from 70+ mph to 0 mph just a sweeping exit about 3 miles every day must save him some gas.
As for safety I would say putting it in N is more dangerous at that speed than not being able to accellerate, can you imagine what would happen if it slips into R(ace).
Thanks for your replies.
--
EJO now a 1993 944T 197K; ex '65 123S; ex '75 245; and ex '81 242GT; also 2001 Kia Sportage, Chrysler 2002 T&C and 2006 MINI Cooper
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EJO,
While at a stoplight I always put her in neutral so I can keep the foot off the brake without lounging forward...
This is the most dangerous place to take your car out of gear. Of the three controls at your command to avoid a collision, only one is availble when stopped; acceleration.
Suppose you see a car sliding on the snow in your mirror? With the car in neutral the reaction time is significantly increased over what it would be to slip your foot off the brake and onto the accelerator pedal. I would rather run a traffic light than be a stationary target for a 3000 pound sleigh coming up behind me.
Reactions are ingrained. Without thought your foot moves from the brake to the throttle and back again as necessary. If you have consciously moved the transmission to neutral, the neural pathways that react RIGHT NOW are unaware of the conscious brain's action. Your immediate reaction will be to subconsciously move your foot between the controls to avoid danger while the car is still in neutral. Now your brain has to recognize that the car is not moving forward, recall the reason why, direct your right arm to move the shift lever, and the right foot back to the throttle. When changing from subconscious reaction to conscious action, the entire process is slowed as the brain makes choices and issues directions. And, there is a finite amount of time necessary for the transmission to physically engage. Snow will cause immediate loss of traction, requiring modulation of the throttle; again adding time to the equation.
The whole process increases the time the car begins to move by at least a factor of five; the difference between .5 second and 2.5 seconds. And, the difference of 42 feet -vs- 230 feet that a car sliding at 30 MPH coming up behind will cover before you begin to move.
If you have time to think about it, it has already happened.
If your engine RPM is high enough to add to braking time, idle speed is too high. Idle speed should be well below the hydraulic coupling speed of the convertor.
--
Mr. Shannon DeWolfe -- (I've taken to using Mr. because my name tends to mislead folks on the WWW. I am a 51 year old fat man ;-) -- KD5QBL
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Shannon
About 3 years ago I had a 12ton plus behemot coming at me in my rearview mirror while at a stop/intersection. I did accelerate but as it was slippery my car (Chrysler T&C) did not lounge forward and the snowplow truck rammed my 5th door in and I was just missed by a car driving thru the intersection.
I know what you are saying but when I drive my manual shift cars I leave them in neutral as I don't ride the clutch.
I have used acceleration with steering many times in my driving career to avoid being sandwiched or side swiped with success, but never acceleration alone.
I get your point but it doesn't work(ed) for me.
--
EJO now a 1993 944T 197K; ex '65 123S; ex '75 245; and ex '81 242GT; also 2001 Kia Sportage, Chrysler 2002 T&C and 2006 MINI Cooper
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