At what point is it advantageous to shut the engine off while driving?

[Mazda_2.3]

Originally Posted by PaleMelanesian

My bro-in-law has a 3s hatch. Watch out for the electric power steering. It stays off, even after you restart the engine, UNTIL YOU DROP BELOW (about) 20 MPH. Then, most likely in the middle of a turn, it kicks back on. It's manageable if you are expecting it, scary if you're not.

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Yeah, I've definately noticed the lack of power steering after restarting. Caught me off guard the first few times but I've gotten use to it. Are there any mods to imrove FE that have been done to your inlaw's 3s hatch? I've got some basic ideas but read last night that the drag coefficient is like .35 and I'm thinkin that is pretty high so I've really got my work cutout for me.

[Mazda_2.3]

Originally Posted by MetroMPG

I've got a kill switch in my car - mounted on the shifter.
Have you got fuel economy instrumentation?
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The kill switch is on my list but I want to pick up the ScanGauge first. I'm actually just waiting on my tax returns to order one. I've heard that the kill switch will need to be able to allow power to continue for the accesories so the ScanGauge doesn't turn off and reset. Haven't figured it all out yet but I should be getting the shop manual for my car in the mail soon. Couldn't believe they didn't have a haynes or chilton manual for my car! I was lucky though and bought the shop manual on CD from ebay for $10.00. From there I can hopefully figure out the kill switch.

[PaleMelanesian]

His is stock. I can see how you could clean up the nose a lot, just by covering the gaping grille. There is NO need for even half that much opening. The shape is good, you could just do some kind of skin over what's already there.

Edit: I see you're getting a Scangauge. Good. It can work with key-off or a kill switch. Just set the Fuel Type to Hybrid. It doesn't receive any updates from the ECU during the brief off-on cycle, but otherwise it's fine. That's all I have. The kill switch is good, but not mission-critical.

[MetroMPG]

Originally Posted by PaleMelanesian

Another source about idling vs shutting down: Is it more efficient to leave your car idling? - By Brendan I. Koerner - Slate Magazine

That's a quality link! Hadn't seen it before. Thanks.

[Chuck.]

Originally Posted by Geonerd

Greetings.

IMO, routinely killing the engine just isn't worth it. Apart from starter and/or clutch wear, you are also beating up the ignition switch. The engine itself also experiences a little extra wear at every stop: The protective film of oil collapses as it slows to a stop and doesn't reform until the engine regains speed. Also, I find that the constant obsessive fiddle-farting to be distracting and tedious. A small engine like yours probably doesn't burn any more than 1/4 gal per hour at idle. Unless you're stuck at a loooong light, train crossing, etc., you're really not saving much.

Since you've got a manual transmission, I'd suggest you read up on specific fuel consumption and pulse/glide driving. The basic notion is that you try to run the engine in it's most efficient RPM/throttle envelope. This is usually found from ~20% to ~50% of redline, and between 40% and 80% of full throttle. (Don't get too close to flooring it, the car may richen the mixture if it thinks you REALLY want to accelerate.) Your variable valve timing will probably extend and distort this zone somewhat, depending on how the ECU is programmed. In practice, all this means is that you short shift and give it a fair amount of gas. This was worth almost 5 MPG city for me.

Actual BSFC (brake specific fuel consumption, or sometimes just SFC.) charts are, unfortunately, hard to find. You might ask the mechanics at the local dealership; sometimes the factory manuals have extra goodies that are not generally available.

30 years ago, there might be a case for this, but with fuel-injectors instead of carbs, and oil that coats the engine much more effectively, pulse and glide does not put the car's hardware at very much risk. Add a FAS switch and you don't need to use the ignition or bump start the car either.

[Wonderboy]

I agree - I think Geonerd has a point in general, that many people, "joe sixpack" would benefit far more by making better habitual improvements like slow/low rpm acceleration, driving 55 on the hwy, or getting instrumentation - the "safe" things. I however think that this is a place more geared to going to the extreme - ecoMODDING, modifying not only your habits, but going to the extreme enough to actually modify your own vehicle to get that 1% better MPG. With that spirit in mind, EOC and shutting your engine off at lights is irrefutably significant in a community where people make their cars look like space shuttles, push their cars around parking lots, and make killswitches for their engines. The "extreme" of shutting off your car at stop lights is nowhere near as extreme as some of the other things people do. It may not be for everyone, and not worth suggesting to some, but I think this is a place where joe sixpack need not apply, and it's reasonable to suggest such methods.

When talking to joe sixpack, however, I probably wouldn't go suggesting EOC and shutting the engine off at lights right away.

[PaleMelanesian]

I do somewhat agree about not pushing the "advanced" stuff to Joe.

However, I think shutting off at lights is one of those "low hanging fruit" things, along with tire pressure and instrumentation. When I'm driving the Odyssey, which doesn't like engine-off at speed, it makes a big difference. Me driving similarly both ways, on my normal routes, with red light shutdown being the major difference. I get mid-20's mpg leaving it to idle, and 30+ shutting it down at lights.

[Mazda_2.3]

Ahead of you on the grill. I'm thinkin that the upper grill alone should be adequate to cool the engine compartment. So, I've cut a 1/16" aluminum insert for the lower grill and am halfway to covering it with black vinyl to spruce it up. It's gonna look a little rougher than I anticipated because the grill curves from left to right but also top to bottom making it difficult to get a good fit w/o the appropriate tools. It should work though and if I like what it does to my MPG I may redo it to look better. I should have a picture of it online by Monday.

Oh and good to hear about the Scangage (that it will work with keyoff).

Originally Posted by PaleMelanesian

His is stock. I can see how you could clean up the nose a lot, just by covering the gaping grille. There is NO need for even half that much opening. The shape is good, you could just do some kind of skin over what's already there.

[TestDrive]

Better to have the opening in the lower grill and close off the upper.
More air going over the relatively smooth top; less air churning under the dirty bottom.

[Mazda_2.3]

I based my decision on the fact that the lower grill was so large and with the OEM belly pan (extends from the front bumper to just past the axles) it seems that a lot of air would be getting trapped in the engine bay. Could you possibly elaborate on why it would be better to block the top grill? Oh, and I have a picture of the grills on my profile.

Originally Posted by TestDrive

Better to have the opening in the lower grill and close off the upper.
More air going over the relatively smooth top; less air churning under the dirty bottom.