Engine Off Coasting - When to do and when not to.

[Bicycle Bob]

Road & Track (?) did some extreme hyper-miling to get 100 MPG once, and found that using the starter was killing them with an automatic shot of gasoline. Bump starting was the winner for them. YMMV I don't switch off for a stop of less than a minute or two.
The other issue is the time it takes for oil pressure to get through the system after any re-start. I try to give it a couple of seconds before I use the accelerator.

[RobertSmalls]

Originally Posted by Arragonis

I'm also wondering what happens to things like ESP with the engine off. I'm willing to try it but I just want to explore the potential consequences.

Just a few points on ACC vs ON. Turning the key to ACC powers down your ECU, wipers, turn signals, Scangauge, ABS, and traction control. In most cars the headlights, horn, and brake lights are among the few things still powered.

You can live without most of those things most of the time, but you're better off with a kill switch, and maybe a Start switch too.

[Arragonis]

RobertSmalls - Thanks - I'm beginning to think the kill switch is the approach to use. I wondered about the ECU though as the "remappers" mod it with the engine off.

B-Bob - Thanks too. I try to leave the engine on if I'm at or near the front of the queue and most of the lights are close to home so I know the sequence. I didn't think about the oil draining point though. I think this engine has a non-return filter but I would need to check. I shall keep engine on for now as its winter and I barely get to normal temp even just with engine on coasting.

[hackish]

Repeated starting does kill the starter. After a start the car also produces a lot more emissions until the cat gets back up to temp. Probably 8-10 seconds on a car that was just running. Many delivery cars that are shut off at every stop will replace a starter every year or so. Unlikely that you will save $300 in fuel with this. It also depends on the starter- some will put up with lots while others die easily under normal use.

The other thing is bump starts are generally considered bad because they break the spring steel straps inside the pressure plate as they're not designed to take load in the opposite direction. A few of my customers are die-hard hyper-milers and I've replaced clutches for this reason. Second time I had a special clutch cover designed with stronger straps so they won't break. Unfortunately he's $1800 behind his fuel savings target having paid for 2 clutch jobs inside a year. If you bump start it in a higher gear and do it gently you will probably greatly reduce the chance of this expensive failure.

[MetroMPG]

Originally Posted by hackish

Unfortunately he's $1800 behind his fuel savings target having paid for 2 clutch jobs inside a year. If you bump start it in a higher gear and do it gently you will probably greatly reduce the chance of this expensive failure.

That's both interesting... and amusing (except for the owner)! What kind of car(s) and how old?

Do you know the driver personally? It would be interesting/instructive to see his technique.

[Daox]

Yeah, it really sounds like your customer needs to learn to bump start more smoothly. I've been doing it for over 30k miles on my Paseo without any hiccups. I know others have gone much longer than I.

[RobertSmalls]

Originally Posted by hackish

Many delivery cars that are shut off at every stop will replace a starter every year or so. Unlikely that you will save $300 in fuel with this. It also depends on the starter- some will put up with lots while others die easily under normal use.

If you're running a delivery service, I think you'll save more than $300 a year by shutting of the engine during each delivery instead of idling. Plus, fewer hours spent idling is better for the engine. Also, the fuel savings is guaranteed, whereas having to replace the starter is unlikely.

Lots of automakers are introducing start/stop technology on their newest engines. I'm not aware of any modifications that need to be made to the engine to accomodate this, so I believe the only components you're placing extra (but acceptable, IMO) stress on are the battery and starter.

[hackish]

Originally Posted by MetroMPG

That's both interesting... and amusing (except for the owner)! What kind of car(s) and how old?

Do you know the driver personally? It would be interesting/instructive to see his technique.

If I remember correctly it was a 2007 Mazda 3 GT 2.3l. I went for a road test with him and he didn't seem to be that hard on bump starting the car. It wasn't side-stepping the clutch by any stretch. I did spent about 15 minutes with the car doing 20-30 gentle start/stops before giving it back to him the second time to make sure the new clutch was bedded. I also told him to avoid his bump starting for the first 1000km. The pressure plate and the disc didn't look like they'd been badly abused and the friction material (even though I replaced it) wasn't severely worn.

[hackish]

I'm definitely not against the economy of shutting down a delivery car. I just don't feel that shutting down your engine for a 5-10 second coast is a good idea. If I manage to buy a 5 gas analyzer this year I might actually be able to test the emissions on a few vehicles to know how bad this really is at the tailpipe.

It is kinda expensive for a science experiment. I have been looking at reflashing a few of the late model cars for better fuel economy. I know we're very successful with diesels. If I could find some successful tweaks for gas powered cars it may afford buying such a toy.

Originally Posted by RobertSmalls

If you're running a delivery service, I think you'll save more than $300 a year by shutting of the engine during each delivery instead of idling. Plus, fewer hours spent idling is better for the engine. Also, the fuel savings is guaranteed, whereas having to replace the starter is unlikely.

Lots of automakers are introducing start/stop technology on their newest engines. I'm not aware of any modifications that need to be made to the engine to accomodate this, so I believe the only components you're placing extra (but acceptable, IMO) stress on are the battery and starter.

[MetroMPG]

Originally Posted by hackish

I have been looking at reflashing a few of the late model cars for better fuel economy. I know we're very successful with diesels. If I could find some successful tweaks for gas powered cars it may afford buying such a toy.

Interesting. If you feel like it, hackish, please post an intro thread. From the bits and pieces I've read so far, I'm curious to know your back story and how you came to be involved with efficiency mods.

Darin