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-   -   At what point is it advantageous to shut the engine off while driving? (https://ecomodder.com/forum/showthread.php/what-point-advantageous-shut-engine-off-while-driving-7124.html)

Mazda_2.3 02-15-2009 01:00 PM

At what point is it advantageous to shut the engine off while driving?
 
Hey everyone, I'm Andrew and yeah this is my first post. I'm trying to figure out if and when I should shut my engine off while driving. At a long stop light? I always do. Coasting down a long down hill straight away? I often do. My real question is at what point does it become advantageous to shut the engine off? Someone once told me the engine uses more fuel to start up than you would use just sitting at idle but I don't think that is necessarily true. Any input?

MetroMPG 02-15-2009 01:06 PM

Your hunch is correct.

A modern fuel injected engine, fully warmed up and in good tune uses very little fuel to re-start. We're talking about an advantage gained after several seconds.

Might want to see:


You may want to take starter wear into consideration as well. (I don't worry about it - I haven't had a bad starter since I had a series of old VW Rabbits when I was going to school. Also, starters are usually easy to remove/repair/replace.)

gascort 02-15-2009 09:27 PM

Andrew, Welcome to EM!

Do you have a manual or automatic tranny?
If you have a manual, see:
Clutch Starting an Engine
If you have the same commute every day, you can determine pretty well where the lights change that are on timers. I clutch start at every light except for 1 or 2 where I know I'm going to have to wait for more than 10 seconds.

Mazda_2.3 02-16-2009 02:18 AM

Great info guys.

My car has a manual transmission paired with the 2.3L 4cyl w/ Variable Valve Timing. The car is all stock with the factory 17" rims. EPA gas mileage is 24/29. I've had the car about 3 weeks and am getting 28 or 29mpg. Not bad but am hoping to make it better. So far I've been coasting as much as possible, downhills and instead of braking. I also shut the engine off at long stops and am shifting pretty early. Unless I'm in fifth, I tend to keep it at around 1500 RPM. Doing 55mph in 5th the tach is at 2800(?), I think.

This is where I am now. Tomorrow I'll start shutting the engine off more often and will start figuring out how to add a kill switch that will allow my accessories to still have power.

Any wisdom or spectacular links from the more experienced folks out there? I'm an apprentice diesel mechanic so I can be a little savy at times. Hopefully any advice you guys can offer won't go in one ear and out the other as a result. Thanks for reading. . . I'll try to keep my posts shorter in the future.

MetroMPG 02-16-2009 10:12 AM

I've got a kill switch in my car - mounted on the shifter. Saves wear on the ignition barrel, and makes it more convenient to use, since I'm usually going for neutral at the same time I want to kill the engine anyway.

FYI, some ideas on how-to...

- http://ecomodder.com/forum/showthrea...-how-4356.html

- http://ecomodder.com/forum/showthrea...itch-5651.html

Have you got fuel economy instrumentation? That'll help more than anything else. It'll motivate you, show you what's working and pay for itself in fuel savings.

Also, in case you haven't seen it:

- 100+ hypermiling / ecodriving tips to increase gas mileage - EcoModder.com

PaleMelanesian 02-16-2009 01:35 PM

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.

Another source about idling vs shutting down: http://www.slate.com/id/2192187/

Geonerd 02-16-2009 01:41 PM

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.

PaleMelanesian 02-16-2009 01:46 PM

60+ mpg says it really IS worth it. ;)

Geonerd 02-16-2009 02:33 PM

In your opinion. :D If you're hardcore regarding FE, go for it! I do think that most people are looking to take a more balanced approach.

I do know that the average Joe watches hypermiler videos of dorks like Gerdes on TV, and just shakes his head. They see him doing insane things like taking freeway exits at unsafe speeds, creeping down the road with 10 cars bottlenecked behind him, slamming the car into gear the second it's started, pushing the car around parking lots, turning the engine off with the car in motion, etc. Joe Sixpack watches all this and thinks, "what an idiot." Joe leaves with the mistaken notion that FE driving is strictly for neurotics, and that there is no point in attempting to improve his own FE. This inability to connect to the general public is a shame, and is something the HM community needs to address.

I'm glad you're getting your 60MPG, but please don't assume that what you do is best for everyone.

MetroMPG 02-16-2009 02:44 PM

Geonerd - I'm not sure how you can be opposed to routinely switching off the engine, then advocate P&G in the next paragraph.

Quote:

you're really not saving much.
You'd better alert the world's auto manufacturers, who are adding idle stop systems to more and more vehicles (non-hybrids) precisely because it saves a significant amount of fuel in urban driving.

Mazda_2.3 02-16-2009 04:35 PM

Quote:

Originally Posted by PaleMelanesian (Post 88076)
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.

[/url]

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 02-16-2009 04:46 PM

Quote:

Originally Posted by MetroMPG (Post 88052)
I've got a kill switch in my car - mounted on the shifter.
Have you got fuel economy instrumentation?
[/URL]

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 02-16-2009 05:11 PM

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 02-16-2009 05:30 PM

Quote:

Originally Posted by PaleMelanesian (Post 88076)

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

Chuck. 02-16-2009 06:28 PM

Quote:

Originally Posted by Geonerd (Post 88079)
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 02-16-2009 06:46 PM

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 02-16-2009 06:56 PM

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 02-17-2009 07:35 PM

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).

Quote:

Originally Posted by PaleMelanesian (Post 88128)
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 02-17-2009 07:49 PM

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 02-17-2009 08:07 PM

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.

Quote:

Originally Posted by TestDrive (Post 88335)
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.


TestDrive 02-17-2009 08:41 PM

Quote:

Originally Posted by Mazda_2.3 (Post 88342)
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.

Seeing the hatch work lower grill (nice looking Mazda3s), I'll change my mind and like leaving the upper grill open better. If the lower grill wasn't such a mess, I'd have suggested partially blocking it in addition to fully blocking the upper. You could probably fully block the lower and still partially block the upper. Take a look at the tiny opening (picture) on basjoos' aerocivic (ugly as sin, but insanely good mileage) which has a full belly pan.

The engine compartment must be designed to vent excess air somewhere. Maybe the front wheel wells??? In any case if you block either grill, there's going to be less air to vent.

Normally it's better to block the upper grill because most cars don't have any sort of belly pan - muffler, mud flaps, oil pan, transmission, steering linkage, struts, ... hanging in the wind, making lots of turbulence. Better to send more of the air over the top where there are fewer obstructions.

PaleMelanesian 02-18-2009 10:06 AM

This is from Phil Knox's photo galleries, book illustrations category. Notice how the lowest nose has the lowest drag. Based on this, I'd go for a smooth upper block first, then block the lower as needed. Even if the car has a fairly smooth bottom, there's the car-ground interaction to deal with, which is more draggy than the free air above the car.

http://ecomodder.com/forum/member-ae...figuration.jpg

Mazda_2.3 02-18-2009 09:00 PM

I will agree that is one ugly civic. Though it's cool that such a small opening is enough to prevent overheating.

I am actually considering doing the uppergrill too but I'll probably get an aftermarket grill first w/o the big bold Mazda emblem.

Quote:

Originally Posted by TestDrive (Post 88347)
Seeing the hatch work lower grill (nice looking Mazda3s), I'll change my mind and like leaving the upper grill open better. If the lower grill wasn't such a mess, I'd have suggested partially blocking it in addition to fully blocking the upper. You could probably fully block the lower and still partially block the upper.


Mazda_2.3 02-18-2009 10:13 PM

Quote:

Originally Posted by PaleMelanesian (Post 88423)
Notice how the lowest nose has the lowest drag. Based on this, I'd go for a smooth upper block first, then block the lower as needed. Even if the car has a fairly smooth bottom, there's the car-ground interaction to deal with, which is more draggy than the free air above the car.

I can kinda see the image going both ways. Yes, less drag with a lower nose but when that low nose has such a huge opening I could see that benifit being cancelled out. This did give me a great idea though.

http://ecomodder.com/forum/member-ma...ibilities.html

just that small opening between the two and perhaps two parallel openings on the lower grill about 1/2" tall each running the length of it. . . hmm...

Wonderboy 02-18-2009 11:35 PM

You may also want to work out some kind of plexiglass covering for the fog light sockets.

Mazda_2.3 02-18-2009 11:56 PM

Definately agree but my goal is for any mod to be removable without
knowing it was ever there. Primarily if I intend to sell it someday but also cause I'm lame and told my girl that nothing would be perminant. Any ideas on how I might go about doing that. I've thought about trying to get lucky at a upullit or on craigslist and finding a bumper that was the same color for cheap but that's not likely. Though if I could, there would be no foglights and no lower grill opening at all. . . . SIGH:o

Quote:

Originally Posted by Wonderboy (Post 88506)
You may also want to work out some kind of plexiglass covering for the fog light sockets.


taco 02-19-2009 01:12 AM

i have had my grill blocked fromt he inside for a few months now, i uses doubloe sided 3m tape(think vent visor tape) it has lasted through 3 snow storms. and is not one bit weak. easy to remove even harder to see. well that is if i painted my coroplast.

i usually get 27-30 mpg, when i was running well like i am now.!!
new wires at 260k miles then a tranny at 155kish miles.



another question what is your drive like, please explain.

Wonderboy 02-19-2009 09:27 AM

@mazda:

I feel the same way about my car even though theres probably no way id be able to sell it at like 190k mi. I havent done any aeromods yet but grilleblocks are definitely easy/effective/temporary enough. As for your fog lights, your regular headlights are probably plenty bright, so if you took the fog light bulbs out, you could either make something that fits in that socket, or hopefully you could take the socket out to put something you're willing to screw into back there. As taco said, some good tape is probably your friend here.

Also, take notice of places where existing screws/bolts are and use those - when i had my corolla and deleted its mudflaps, i was poised to make rear wheel skirts because of the existing holes i could bolt into. There mmay be options like that up front on that mazda you could take advantage of w/o drilling any holes.

PaleMelanesian 02-19-2009 10:10 AM

Wonderboy, take a look at what I've done on my car: Aero mods - new grill block and wheel covers - CleanMPG Forums Plexiglass upper block, and foam mat press-fit into the lower.

Mazda_2.3 02-19-2009 07:13 PM

Definately need to look into the 3M tape option, probably a lot easier than what I'm trying to do now w/ sheet metal and vinyl. My drive is about 11 or 12 miles at 6:30AM so pretty cold (frost on windows and wet roads). It's about 3/4 freeway and there are . . . 7 stoplights (engine off at most) and a MAX (passenger train) crossing on the other 1/4. Few gradual hills here and there but nothing that isn't compensated for by coasting down after. Oh, Highway speed is 55 and I keep to the slow lane.
Quote:

Originally Posted by taco (Post 88523)
i have had my grill blocked fromt he inside for a few months now, i uses double sided 3m tape.

question: what is your drive like, please explain.


Mazda_2.3 02-19-2009 07:20 PM

Wonderboy:

That is definately something I'm going to have to take a look at once my grill blocks are finished. I haven't used the foglights yet at all and the Headlights are definately bright enough. I could definately see some sort of foam plug cut to fit and coated or maybe even plexi being used and fastened from the back w/ the factory holes.

Heck, even making my own holes, if you can't see them they aren't really there.

taco 02-19-2009 11:15 PM

Not too awful of a trip rolling resistance will help u alot. Put at least 40psi in the tires

3 m molding tape is wonderful. Lasted in a 1 .5 hr commute in a blizzard where the road wasn't no where to been seen we got about 8 inches that night (work nights) that was fun but no change in adhesion even with neg. Temps. Also had it too 100 mph and it hold great.


I wannasee 35-40 mpg out of that car!

Mazda_2.3 02-20-2009 01:10 AM

Definately, 40 would be great! I'll have to take a look at my tires. I have those sensors that sound an alarm if they get to low so I've never actually checked them (only had the car 2ish weeks) Wonder if it alerts when the pressure is to high. . . Probably/hopefully not. Gonna look into how I could tape a block in behind the grill on Saturday.

Think there would be slightly more drag from a block inside than outside?

Quote:

Originally Posted by taco (Post 88654)
Not too awful of a trip rolling resistance will help u alot. Put at least 40psi in the tires

I wannasee 35-40 mpg out of that car!


TestDrive 02-20-2009 02:55 AM

Quote:

Originally Posted by Mazda_2.3 (Post 88671)
I have those sensors that sound an alarm if they get to low so I've never actually checked them (only had the car 2ish weeks)

Don't know about your vehicle in particular, but at least some of those are just ECU monitoring anti-lock speed sensors. Absolute pressure isn't monitored, just difference in average rotational speed for each tire. Too large a difference between tires and you get an alarm.


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