Shifting into Neutral to Save Gas? - 986 Forum - The Community for Porsche Boxster & Cayman Owners

JCL12 · 08-06-2007, 03:16 PM

What do you all think of this:

My box is a tiptronic. Despite the auto-trans, my box has some pretty darn strong engine braking. (I am not used to this)

When coming to a spotlight or going down a hill, what do you all think of putting the car into neutral to eliminate engine braking and coast with less friction? Although it'll definetly save me some gas, is frequent "shifting" from drive to neutral going to cause premature wear and tear on the transmission?

Thoughts and comments?

08-06-2007, 03:57 PM

Just my 2¢...

I don't think it's worth it. My belief is that the auto tranny shifter was not designed to be shifted so frequently, otherwise it would be so noted in the owners manual. AFAIK, there is no car manufacturer that recommends this technique.

To my chagrin, my father and brother still do this, after debating it with them. To each their own.

Even Steven · 08-06-2007, 04:05 PM

Quote:

Originally Posted by JCL12

What do you all think of this:

My box is a tiptronic. Despite the auto-trans, my box has some pretty darn strong engine braking. (I am not used to this)

When coming to a spotlight or going down a hill, what do you all think of putting the car into neutral to eliminate engine braking and coast with less friction? Although it'll definetly save me some gas, is frequent "shifting" from drive to neutral going to cause premature wear and tear on the transmission?

Thoughts and comments?

Actually, it will not save you any gas. A little known fact about modern engine management systems is that they have the ability to cut off the fuel pulse entirely when coasting, such as a long downhill grade. Now, I'm not a Porsche mechanic, so I'm not 100% sure that Porsche does this, but I do know for a fact that most other manufacturers program their engine management systems to do this in order to raise their average fuel economy.

So the next time you're coasting down a hill, if you put your transmission into neutral, remember that you're forcing the computer to send fuel to your engine to keep it idling. If you were in gear instead, the fuel pulse may be shut off entirely by the engine management system, thus increasing your fuel economy.

If you doubt this, just do a little bit of research on the Internet and you'll discover it's true.

08-06-2007, 04:32 PM

Also from a safety perspective, it is best that you are in gear, in the event you need to avoid, or maneuver, around something.

TriGem2k · 08-06-2007, 04:34 PM

Who SERIOULSY buys a Porsche thinking "Well it’s good on gas"???

Today I took my car to work with me just for fun.

I went to the bank, parked the car, left the Car & A/C running for 20mins, came back, drove to another bank, parked my car, left the Car & A/C running for about 35mins, then drove it back to my office. Shifted gears between 4-5.5k RPM every time.

When a car is this much fun, who cares about an extra 5MPG?

Maybe you should just buy a Prius and then shift that into neutral & turn off the engine while coasting.

vipola · 08-07-2007, 06:35 AM

Ouff.. Ideling like that is NOT good for a engine!..

Quote:

Originally Posted by TriGem2k

Who SERIOULSY buys a Porsche thinking "Well it’s good on gas"???

Today I took my car to work with me just for fun.

I went to the bank, parked the car, left the Car & A/C running for 20mins, came back, drove to another bank, parked my car, left the Car & A/C running for about 35mins, then drove it back to my office. Shifted gears between 4-5.5k RPM every time.

When a car is this much fun, who cares about an extra 5MPG?

Maybe you should just buy a Prius and then shift that into neutral & turn off the engine while coasting.

TriGem2k · 08-07-2007, 11:01 AM

AHAHAHHAHA good one Grizz. I'll take my chances though, the A/C sure keeps the car cool in the heat.

Rick, its not about throwing money away, I'm spending the money in order to be comfortable when I get back to my car and not burn my bottom when I sit down. Since your house is on a hill what are you going to do about premature brake fade?

Vipola, neither is turning on and off your engine all day long for short amounts of time. I'll take my chances letting my engine idle.

rick3000 · 08-07-2007, 07:31 PM

Quote:

Originally Posted by TriGem2k

Since your house is on a hill what are you going to do about premature brake fade?

I park in the garage.

Dr. Kill · 08-08-2007, 07:45 AM

Quote:

Originally Posted by TriGem2k

AHAHAHHAHA good one Grizz. I'll take my chances though, the A/C sure keeps the car cool in the heat.

This is a risk. You might want to consult your insurance policy. I am under the impression that mine will not cover theft if I have left the keys in the car, or left the car running.

Back2DTM · 08-07-2007, 12:32 PM

Wow that is very bad for your car, bud.

Quote:

Originally Posted by TriGem2k

Who SERIOULSY buys a Porsche thinking "Well it’s good on gas"???

Today I took my car to work with me just for fun.

I went to the bank, parked the car, left the Car & A/C running for 20mins, came back, drove to another bank, parked my car, left the Car & A/C running for about 35mins, then drove it back to my office. Shifted gears between 4-5.5k RPM every time.

When a car is this much fun, who cares about an extra 5MPG?

Maybe you should just buy a Prius and then shift that into neutral & turn off the engine while coasting.

JCL12 · 08-07-2007, 02:00 PM

Back to the initial topic -

Bottom line: Is going from D-->N to eliminate engine braking for gas saving purposes (down hills and red lights) going to be bad on the tranny or not?

skip_168 · 08-07-2007, 02:05 PM

Quote:

Originally Posted by JCL12

Back to the initial topic -

Bottom line: Is going from D-->N to eliminate engine braking for gas saving purposes (down hills and red lights) going to be bad on the tranny or not?

the tranny can take it, but itz alot of wasted effort on your part...

Even Steven · 08-07-2007, 05:10 PM

Quote:

Originally Posted by JCL12

Back to the initial topic -

Bottom line: Is going from D-->N to eliminate engine braking for gas saving purposes (down hills and red lights) going to be bad on the tranny or not?

Did you read my post? You will not save gas by going into neutral...you'll actually use more gas by doing that.

Perfectlap · 08-07-2007, 02:11 PM

The Boxster has AC?

NICE! could never figure out what all those buttons with snow flakes meant.

If its above 60F, the top is down....People always accuse me of going tanning at the fake bake. I tell them its true I have a tanning machine, it has a 250 HP boxer engine straight from Stuggart.

zackwatt · 08-07-2007, 02:35 PM

Quote:

Originally Posted by Even Steven

Actually, it will not save you any gas. A little known fact about modern engine management systems is that they have the ability to cut off the fuel pulse entirely when coasting, such as a long downhill grade. Now, I'm not a Porsche mechanic, so I'm not 100% sure that Porsche does this, but I do know for a fact that most other manufacturers program their engine management systems to do this in order to raise their average fuel economy.

So the next time you're coasting down a hill, if you put your transmission into neutral, remember that you're forcing the computer to send fuel to your engine to keep it idling. If you were in gear instead, the fuel pulse may be shut off entirely by the engine management system, thus increasing your fuel economy.

If you doubt this, just do a little bit of research on the Internet and you'll discover it's true.

You Sir, Are Correct.

Modern engines use NO fuel to coast to a stop. In neutral there is no longer a mechanical linkage to the road to drive the rotation of the engine. Therefore something must be done to "run" the engine, so engine management must start the fuel flow.
Just think, you are getting those last few feet for FREE. YAY!

JCL12 · 08-07-2007, 02:58 PM

Quote:

Originally Posted by zackwatt

You Sir, Are Correct.

Modern engines use NO fuel to coast to a stop. In neutral there is no longer a mechanical linkage to the road to drive the rotation of the engine. Therefore something must be done to "run" the engine, so engine management must start the fuel flow.
Just think, you are getting those last few feet for FREE. YAY!

To Clarify: you are saying that when you coast in drive, all fuel flow ceases and engine RPM is maintained by absorbing the cars kinetic energy, effectively slowing it down faster but using zero gas?

Even Steven · 08-07-2007, 05:14 PM

Quote:

Originally Posted by JCL12

To Clarify: you are saying that when you coast in drive, all fuel flow ceases and engine RPM is maintained by absorbing the cars kinetic energy, effectively slowing it down faster but using zero gas?

Yes, in a nutshell. It's not quite that simple, but the fact remains that a modern fuel management system has the ability to shut off the fuel pulse completely when a vehicle is coasting. Think of it this way--Why should the engine management system waste fuel by sending it to engine engine in a car coating down a hill? Fuel isn't required in such a situation, so it can simply be turned off. If you put the transmission into neutral while coasting, you are forcing the engine management system to start sending fuel to the engine to keep it idling. Therefore, it is more economical to leave the car in gear and coast down a hill instead of popping it into neutral and coasting down the hill.

Like I said earlier--do a little research and you'll learn all about it. I happened to learn this stuff in school

spark00 · 08-08-2007, 04:23 AM

Quote:

Originally Posted by Even Steven

Yes, in a nutshell. It's not quite that simple, but the fact remains that a modern fuel management system has the ability to shut off the fuel pulse completely when a vehicle is coasting. Think of it this way--Why should the engine management system waste fuel by sending it to engine engine in a car coating down a hill? Fuel isn't required in such a situation, so it can simply be turned off. If you put the transmission into neutral while coasting, you are forcing the engine management system to start sending fuel to the engine to keep it idling. Therefore, it is more economical to leave the car in gear and coast down a hill instead of popping it into neutral and coasting down the hill.

Like I said earlier--do a little research and you'll learn all about it. I happened to learn this stuff in school

This is interesting. Is this same for manual transmission also? I tend to leave my shift on neutral when I'm coasting to stop. I would like to save gas for environmental reason if I can. haha.

kras · 08-06-2007, 06:55 PM

I'm looking to buy a boxster. This is one thing I noticed in my test driving that I didn't like. The tiptronic down shifts sometimes when I don't want it to.

I know that there supposedly are several different modes that the transmission will choose from and I was wondering if there is a mode that doesn't down-shift.

djomlas · 08-06-2007, 07:19 PM

Quote:

Originally Posted by kras

I'm looking to buy a boxster. This is one thing I noticed in my test driving that I didn't like. The tiptronic down shifts sometimes when I don't want it to.

I know that there supposedly are several different modes that the transmission will choose from and I was wondering if there is a mode that doesn't down-shift.

just get a manual, its a fun car. why would you want a car to shift for you?