Do manuals coast farther then automatics?
 

I have been thinking about this the past few days, and I figure I would just ask. Do manuals coast farther than automatics? Both in neutral. Lets say you drive the automatic and manual on the same exact piece of land, at the same speed put both cars in neutral, which one will coast farther?

Which, IN or OUT of gear(s)?

Manuals have LESS overall power loss (~12-15%) AND can be placed in NEUTRAL, but some gears are always engaged.

Automatics have MORE overall power loss (~15-20%) BUT are never completely disengaged due to combination of pump and torque converter operations.

In theory, the automatic will. Automatics weigh more, and all things being equal, adding weight adds momentum. Imagining like you said, both in neutral at the same speed in the same spot with same conditions, adding weight will increase the coast distance. Granted it's not too much weight, standards have weighed less in every vehicle I have compared the two transmissions.

Being about 100lbs heavier then standards hauling that heavy automatic transmission costs you fuel just in its shear weight let alone its friction losses.

Most of the wasted fuel caused by the automatic trans is due to the lack of early/lower rpm high gear engagement, I suspect you could due very well with a gear selectable automatic trans.

An automatic will win in this regard- it should coast further, all other things being equal.

2 feet further ? 10 feet further ? might friction losses cancel it out ?

What friction occurs when it's not in gear? I didn't think there was any.

input shaft is still spinning

But perhaps that's not a real good argument as the standards transmission is as well , only with lighter fluid viscosity

I am not aware of the differences between the standard and auto, I was only aware of the weight difference. I couldn't speak to the input shaft, but I imagine if both have then it would be working the same.

Where does the auto trans fluid pump get its power? Is it a parasitic load on the trans directly, indirectly via the engine, or more indirectly via some electrical system drawing on the battery?

Woah, thanks for the replies guys. What about with the clutch pushed in on the manual? Would that make anything of a difference?

Shouldn't, but one could shift out of gear and release the clutch.

I would expect the manual to coast a little farther in gear because it wouldn't be so slippy as an automatic, but on neutral the difference might be negligible.


I have never seen an electric ATF pump.

I don't understand what this is, or how the slippiness would influence it coasting out of gear. :confused:

The fluid pump is turned by the engine directly by drive teeth on the back of the torque converter body. Whenever the engine is running, the pump is being turned. I would argue that its energy consumption is negligible in the big picture, but still takes slightly more energy that a manual transmission in neutral.

This has no overall effect on coasting distance. Coasting distance is very similar between an auto and manual transmission, but you are using slightly more energy if you are idling with an automatic while doing so.

Both a/ts and m/ts have plenty of gears, shafts, and bearings which continue to spin if the vehicle is coasting whether it's in neutral or not and whether the engine is on or off and whether the clutch is engaged or not. The exceptions are those very uncommon vehicles that can freewheel. I'm not sure, but I suspect that if the only variable is if the transmission is auto or manual, the coasting distances would be very similar.

I'm wondering what prompted the question and what will we do with the answer?

Many but not all a/ts should not be coasted extended distances with the engine off due to lack of transmission lubrication. Most m/ts are splash lubricated; the simple fact that bits are spinning in the oil lubricates them and no pump is required. So if I wanted to do extended coasting- presumably the reason I want to coast in the first place is to have the engine off to save fuel- I'd prefer to have a m/t.

Clutch in or out makes no difference whatsoever because it is on the wrong end of the transmission for disrupting the transmission-to-wheels connection.

I EoC (Engine on Coast) for a good 11-13 miles on my way home from work everyday, and I barely lose any speed while coasting, with my old Camry, I could coast for an extremely long time before I would have to accelerate again, which I now suspect was because of the heavier weight. If manuals coasted better, I could probably engine off-coast with a manual for about 8 of that if manuals coasted any better. Due to this information from all you guys, there isn't a doubt in my mind that I am getting a manual when I get the rest of the settlement from my car accident. Right now I have 800$ and am trying to find an old beater, but they are extremely hard to find in Cali due to the strict smog requirements. I can find them all day around my uncle who lives in Washington, but not here.

Here is the stretch of freeway I get to coast on. Note however, I do have to climb that everyday and I only average 28-33mpg the entire time.

https://www.google.com/maps/dir/34.3...m3!4m2!1m0!1m0


[Edit]: Only reason I don't engine-off coast now is because I enjoy my auto tranny intact.

Another edit: Here is my route to work everyday: https://www.google.com/maps/dir/1480...34.2112961!3e0

It's a shame your uncle can't buy a car and you just drive it from time to time.

Wink.

I literally just asked my mom this last night haha, but I don't think an old beater would survive the 1,100 mile drive home from his house to my house :P

Coasting on neutral it would be less noticeable than coasting on gear, unless the automatic transmission has that neutral-coasting feature like the one used in the Saturn Astra.

Ok guys, now for my final question, which is more productive for EoC, coasting with engine off and clutch pushed in, or coasting with engine off and car in neutral? Talking about a manual here, not auto.

I do both and don't really notice a difference between the two.
When I've got clear road behind me I P&G between 55 & 35 in neutral with my foot off the clutch so I don't have to Fred Flintstone the clutch the whole time.
When I'm in traffic my P&G is more like 55 to 45, so the glides are shorter. I usually clutch it then, but even then I'm throwing it in neutral sometimes.

It should be a small difference, but neutral would be better. In gear with the clutch pushed in, you will be spinning more parts (clutch disk, input shaft, related bearings, etc). There is not a lot of friction here, so it's probably not a big deal either way.

The pilot bearing is intended to be used intermittently, so I would have concerns for long-term life of the pilot bearing if you regularly coasted in gear with the clutch pedal depressed.

Coasting with a gear engaged and the clutch depressed may be useful to bump-start, saving the starter and the battery.

If your coast is going to be relatively short pushing the clutch in would be the better choice.
A) Your going to press the clutch in anyways even if you wanted neatreal .
B) Why waste time then shifting it out of gear waiting 9.5 seconds then repress the clutch Put back into the gear when a simple press of the clutch is all thats needed, in the case of a short coast.

Once the clutch is pressed it disengages the drive from the gears, same as when in neutral. The clutch is only actively being worn when changing gears or first pressing it, not holding it pressed in.