Is it OK to roll down a hill in neutral with the engine off?

Alan Cesar wrote:

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.

It will come. That, and the EU test is pretty lame.

That, and some stop-start does run closed loop right away- they never turn the sensors off. finally, the amount of fuel to restart normally is more a matter of who calibrated it than how much it really needs...

OP- since you are creeping down a hill, it won't hurt the trans.

I know that bump-starting an engine that dies on the highway, over and over again at 60mph+, will eventually kill it. : )

This is a line at school? I'd say change schools because you are obviously not learning enough to figure out how to beat traffic!

Racer1ab wrote: And now, thanks to the advent of GPS tracking, it's a fireable offense at nearly any trucking company.

If I stop a driver and have a chat for five minutes, they call. The GPS tracking is insane. I just tell him to put me on and I'll explain how "long the line is." Can't argue with scurrity. < /off topic rant >

Keith Tanner wrote:

Knurled wrote:

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.

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've used to see some pretty scary E36 M3 happen on the west side of the Eisenhower tunnel when I'd commute between Denver and Vail pretty regularly. I NEVER want to be a truck driver just from seeing those shenanigans go down.

In reply to Keith Tanner:

Hit the jakes!!!!!

Gearheadotaku wrote: vs. the uphill both ways we all had to deal with!

Through 6 feet of snow in July.

Mmadness wrote: 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 dont know the Volvo auto tranny in this but if it is a ZF, odds are the tranny pump is driven by the input shaft which is probably not turning when the engine is off. If so, the lack of fluid pressure would cause wear in bearings and failure.

Not all auto trannys are made this way. Odds are if the owners manual advises against flat towing, a lot of it is for this reason.

Mmadness wrote: 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.

automatic transmissions have no rear pump any more. So coasting with the engine off is not a good idea and you won't be able to bump start it.