coasting a GM in neutral not economical?

[star_deceiver]

Coasting downhill in 5th gear @ 90km/h nets me about 125ish mpg. Coasting down the same hill in neutral at 90km/h gets me about 200+mpg according to the ecometer. I don't doubt that the results are quite similar when coasting/decelerating to a stop at a red light. This is from the 2ZR-FE 1.8L w/5spd stick common to the 09+ Vibe/Corolla/Matrix/XD.

The benifit of coasting in neutral is saving the clutch, which many can attest to, is a lot more expensive then replacing your brake pads!!!

[Mustang Dave]

The benifit of coasting in neutral is saving the clutch...

How does coasting in neutral save the clutch?

[Thymeclock]

Originally Posted by Mustang Dave

How does coasting in neutral save the clutch?

If you could live in a world where you never had to apply the brakes, they would never wear out. If you could live in a world where you never had to use the clutch, it would never wear out.

I know that would be in a hypothetical world, not the real world. However, the same universal principle still applies: the less you brake, the longer your brakes will last. The less you clutch, the longer your clutch will last.

[NeilBlanchard]

It is better for the clutch to coast in neutral rather than holding the clutch pedal down.

Do you think a clutch is worn by the number of times it is used, or more by how well/badly it is used?

[basjoos]

A clutch is worn out by how much slippage it gets as you engage it. The clutch lining is like brake lining in that a little of it gets scraped off each time you engage it when the engine and transmission are spinning at different rpms. As it speeds up or slows down the engine until it matches the transmission rpm, it is rubbing off clutch lining. If you did mostly highway driving and rev matched each time you changed gears while in motion, the transmission bearings would wear out long before the clutch lining would. If you did mostly city driving in a hilly location, often towed a trailer, and didn't rev match when changing gears, the clutch lining would be the first to go.

I've heard people saying that if you spent a lot of time coasting with the clutch pedal pressed down so the clutch was disengaged, it would wear out the throwout bearing, but I have never had one fail. When Greasemonkee replaced my transmission after 515,000 miles, a 5th gear journal bearing had failed, but it still had 1/3 of the clutch lining left and throwout bearing was fine.

[redneck]

Originally Posted by NeilBlanchard

It is better for the clutch to coast in neutral rather than holding the clutch pedal down ?

Yes it is better for the clutch to coast in neutral rather than holding the clutch pedal down. The reason is because when the clutch is depressed the throwout bearing has to spin. This can lead to early bearing failure. Unlike big rig throwout bearings that are greasable, car throwout bearings are not greasable. In normal use, the throwout bearing will last as long as the clutch lining does.

However, by only pressing in the clutch, you will save wear and tear on the transmission synchronizers.

Synchronizers allow the gears to engage easily when shifting by helping to synchronize (match) the speed of the gear being selected . If your coasting down the road in neutral at speed and wish to put the transmission back into gear the synchronizer for that gear must now attempt to slow the transmission enough to allow the gears to engage. Since synchronizers are commonly made of brass to keep form chiping and or damaging the gears, exccessive wear can result.

By using a combination of the two methods, wear could be minimized.

Short coasts - push clutch = save synchronizers

Long coasts - place in neutral = save throwout bearing

Do you think a clutch is worn by the number of times it is used, or more by how well/badly it is used?

Clutch wear only occures when the clutch surface is not in constant contact. Constant slipping allows heat, glazing and wear to occure. Abrupt use can cause the linning to tear and fail.

To minimize wear, one needs to learn the minimal amount of slippage needed to fully engage the clutch.

>

[gone-ot]

...there's clutch plate wear and there's throw-out bearing wear.

...and, they're caused by different mechanisms.

[DonR]

I can tell you that my 97 Suburban & my 2009 Pontiac G8 do not utilize DFCO very well, if at all.

The Suburban has been verified by my scanguage, (which also will erase the radio memory overnight).
According to the Wife's hot rod's Driver Information Center (DIC) I can only get to about 100 mpg engine breaking in gear (DFCO). I haven't tried the scanguage in it yet.

I don't know if it is because the suburban in older & the Pontiac is Australian or what, but I wouldn't say all GM products use DFCO.

Don

[Thymeclock]

Originally Posted by NeilBlanchard

Do you think a clutch is worn by the number of times it is used, or more by how well/badly it is used?

Both. With use comes wear, and everything wears out eventually.

Clutch wear only occures when the clutch surface is not in constant contact. Constant slipping allows heat, glazing and wear to occure. Abrupt use can cause the linning to tear and fail.

To minimize wear, one needs to learn the minimal amount of slippage needed to fully engage the clutch.

Wear can be minimized by proper driving habits, but not eliminated. Brakes, as I mentioned, are a better example. The more you have to brake, the sooner your brakes will wear down. If you ride the brakes you will cause premature brake wear. But most braking is an unavoidable necessity.

[Thymeclock]

Originally Posted by DonR

I can tell you that my 97 Suburban & my 2009 Pontiac G8 do not utilize DFCO very well, if at all...

...I don't know if it is because the suburban in older & the Pontiac is Australian or what, but I wouldn't say all GM products use DFCO.

Don

I think you are right. I'm not convinced either, as I don't see any evidence of my '09 Aveo utilizing it. After all, it is the cheapest car that GM produces.