Where I go to school, there is a twenty minute wait to get into and out of the parking lot each morning which is downhill both ways (about 1/4mi.). Lately, I've been shutting off my car (Volvo S60R automatic) and coasting in neutral. Will this do any harm to the transmission or AWD?
I don't see any harm at that low of a speed. Beware of no power steering or brakes though.
I don't see any real benefit, either. It may be saving you a couple tablespoons' worth of gasoline but that's about it.
Unless you suddenly need power, no. Note that rolling an auto like that, some 60s stuff aside will mean you're spinning things that get pressure lubrication, that only get oil pumped in with the engine running. A few miles wont hurt, but many will burn it up. Also, starting the engine takes a lot of gas relative to idling it. I'd probably just let it idle in neutral, and I try to hypermile when I can.
My grandfather use to do this when he delivered ice back in the day, (yes that long ago). He thought it was the best way to save gas as he came down the mountains. Until one day he went to start the truck and it didn't start. So he continued to coast until he got all the way down the to the bottom. Of course it was at the bottom of a valley where a train also opportunistically ran through. Yup, Im going to tell you a train came through and wiped the truck out, because that's exactly what happened. The gas of course was worth less than the truck.
Mmadness wrote: which is downhill both ways (about 1/4mi.)
I just want to know how this part works 
(I know, I know, different entrance/exit, gain altitude in parking... it just reads funny)
vs. the uphill both ways we all had to deal with! 
My father as an IH dealer back in the thirties. There was some problem with driveshaft failure. Turns out the drivers were coasting down a long hill and the shafts were exceeding their designed rpm. that was his story anyway.
stuart in mn wrote: I don't see any real benefit, either. It may be saving you a couple tablespoons' worth of gasoline but that's about it.
I wanna see the car that will idle for 20 minutes on a couple tablespoons of gasoline.
I think mine will go through a half gallon idling for that long. I remember that I figured I would get about 35mpg if I just left it idling while towing it on a trailer.
iceracer wrote: My father as an IH dealer back in the thirties. There was some problem with driveshaft failure. Turns out the drivers were coasting down a long hill and the shafts were exceeding their designed rpm. that was his story anyway.
That makes no sense.
I'm betting that back in the 30s, some cars could go faster downhill in neutral than they could go on level ground. The "fast" Ford V-8s had what? 85 HP? The IH delivery trucks probably had much less than that.
and had very steep gears.
Honestly, I would like to know who started the whole "it needs more gas to start than to leave it idle" if this was true, then BMW would not be offering the "start stop" mode as part of their gas saving agenda. With it on, their engines will shut down if you sit at idle for a certain period of time and restart as soon as you go to move again.
If it didn;t save gas, I doubt BMW would do it.
Trans_Maro wrote:iceracer wrote: My father as an IH dealer back in the thirties. There was some problem with driveshaft failure. Turns out the drivers were coasting down a long hill and the shafts were exceeding their designed rpm. that was his story anyway.That makes no sense.
Clearly, you've never heard of Georgia Overdrive
Urban whatever said: n. Trucker-speak for coasting down a hill or more often a mountain with the transmission disengaged. 18-wheelers can only go so fast, and the engines slow them down when coasting, so to go faster they take the engine out of gear. Runaway truck ramps were built for people who do this..
Really?!
I believe it is against the law some places. How you'd get caught without hitting something I don't know.
An old carburetor motor would probably use more gas to cold-start than idling for a few minutes. But anything fuel injected will start using less gas than needed to idle for 30 seconds.
Wait a second - so this is happening while you're waiting in line to get into the parking lot, and traffic is just creeping along? If that's the case it's probably not a big deal.
bgkast wrote:Urban whatever said: n. Trucker-speak for coasting down a hill or more often a mountain with the transmission disengaged. 18-wheelers can only go so fast, and the engines slow them down when coasting, so to go faster they take the engine out of gear. Runaway truck ramps were built for people who do this..Really?!
I think signals were crossed somewhere.
There was a long and interesting thread on eng-tips regarding truck brakes and runaways. Interesting for me because I'm not a truck driver but I recognize that drums are still used on Big Trucks because they pack the most stopping power in a given package size, at the expense of heat issues. It's worse than for cars because it takes air pressure to disengage the brakes, meaning that there is going to be a maximum braking available when there is zero air pressure, and when the drums expand when super-hot there is little to no braking available.
Anyway, you need to crawl down the steep/long slopes using an engine brake which, in a roundabout way, converts the energy of braking into coolant heat. As long as you don't miss a downshift. Then you can be quite boned if you don't have the braking capacity to get the truck slowed down enough to get it into a low gear again.
Cone_Junky wrote: An old carburetor motor would probably use more gas to cold-start than idling for a few minutes. But anything fuel injected will start using less gas than needed to idle for 30 seconds.
cold start yes.. the choke would kick in. But once warmed up, no extra fuel would be needed. I had a Fiat 124 that would start with a single hit to the starter from hot. It did not even need to rotate the engine a full revolution.
Even a already warmed up efi motor runs open loop(rich) for a little while when you start it.
Kenny_McCormic wrote: Even a already warmed up efi motor runs open loop(rich) for a little while when you start it.
Not long enough to matter. Also: BMW isn't the only company using start/stop technology. Nearly every car sold in Europe has this feature. Because it pays off.
We don't see it much stateside because it doesn't have much effect on the EPA ratings because of the way our gov't runs tests. Under Euro testing, it does.
Trans_Maro wrote:iceracer wrote: My father as an IH dealer back in the thirties. There was some problem with driveshaft failure. Turns out the drivers were coasting down a long hill and the shafts were exceeding their designed rpm. that was his story anyway.That makes no sense.
Heavy duty trucks in the 30s cruised at 45 tops.
Knurled wrote:bgkast wrote:I think signals were crossed somewhere. There was a long and interesting thread on eng-tips regarding truck brakes and runaways. Interesting for me because I'm not a truck driverUrban whatever said: n. Trucker-speak for coasting down a hill or more often a mountain with the transmission disengaged. 18-wheelers can only go so fast, and the engines slow them down when coasting, so to go faster they take the engine out of gear. Runaway truck ramps were built for people who do this..Really?!
Yeah, the "out of gear to go faster" thing is obviously wrong to anyone who's spent time near trucks on mountain passes. You can smell the brakes as they try to keep those rigs under control and you can hear the compression brakes purring.
CW McCall even wrote a song about it. http://www.youtube.com/watch?v=C5A8COF_NYQ
I was told by a trucker that it is illegal.
And now, thanks to the advent of GPS tracking, it's a fireable offense at nearly any trucking company.
Some companies will even penalize you with an overspeed violation if you go faster than their governed speed down a long grade.
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