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03-17-2010, 05:07 PM | #1 |
Ignition vs. Roll start?
I must say I am impressed that with the Yaris mileage obtaining 40mpg over 1368 miles with a good mix of long freeway driving through New York and Massachusetts on winter fuel and tires. I cannot wait for summer!
However, I have a question. There are a lot of hills in my area and I often find places to cost for over a quarter of a mile. For these I turn of the car and let it roll and am even able to roll into and park my car in the school parking lot after .2 miles of costing and over 360 degrees of turning. Most of my coasting, though, is when I see a red light in the distance. Sometimes the light turns green and I love the extra mpg boost from not having to start from a full stop, but I would like to know: --> Which is better? Roll start the car in an appropriate gear? Or use the ignition system to start the car? Also, many say the wear and tear of ignition is similar to 7 seconds of the engine being on, so I turn my car off for nearly every light and am debating about turning off the car to roll up to stop signs... is there too much of a good thing? I do use the fuel shutoff DFCO (sp) as well, but I find I would rather just turn the car off and coast for greater distances. Also, did I notice that the ODO only counts when the car is actually in the on position? After driving an SUV, the lack of power steering in the Yaris feels like the power steering in my Xterra, and it seems the break hydraulics only repressurize when the engine is on. I cannot afford a Scangauge, but do I have to turn the car back to the on position without igniting the engine to have a more accurate mileage calculation? Plus, it gets a little cranky and likes to turn the engine back on if it has not spun down fully and it is a bit distracting to have to turn the car on and off several times to finally but the engine to sleep. Is this true for the other hypermilers? It's funny, sometimes I feel like my car is off more than it is on! Thank you Alypuppy 09 HB Manual Trans. Last edited by Alypuppy; 03-17-2010 at 07:41 PM. |
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03-17-2010, 08:46 PM | #2 | |
Steals terrorist's lunch
Drives: 2007 Yaris Liftback Join Date: Mar 2007
Location: Reno, Nevada, USA
Posts: 1,299
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It sounds like you're off to a great start with hypermiling! When you are moving at anything faster than 10 MPH and want to restart, bump start in 5th and then quickly shift to the appropriate gear and go. I do this several times per day. Correct, the odometer only increments when the ignition switch is in the "On" position. This is also the necessary switch position for the electric power steering assist. Yes, the difficulty with turning the engine off is normal in this car. I'm not sure why but I think it is due to the fuel that is queued up on the rail when we stop the engine at higher RPM. My trick is to cycle the ignition switch to the "Off" position, count to two-one-thousand, then cycle it back to the "On" position.
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- Brian Share the Road I often carry 2 carpool passengers and mountain bikes or snowboards/skis over a 4,500 foot elevation difference. Click the graphic above to see my detailed mileage logs. |
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03-17-2010, 09:11 PM | #3 |
Thank you Brian! =o)
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03-17-2010, 10:26 PM | #4 |
Drives: 2008 Yaris Sedan Join Date: Feb 2010
Location: Oklahoma City, OK
Posts: 323
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Just drive normally. The Yaris is smart enough to cut the fuel completely when:
1. The accelerator pedal is at idle position. 2. The transmission is in gear. 3. The clutch is engaged. 4. Engine speed is above 1100 rpm. (I think it's 1100 anyway.) 5. Engine is at normal operating temperature. Your fuel consumption will be zero under those conditions. Not even the normal 0.2 GPH for idling will be used. Search for "DFCO", or "Deceleration Fuel Cut Off". -Steve |
03-18-2010, 10:24 AM | #5 | ||
Drives: 2013 Chevy Spark 1LT 5-speed Join Date: Oct 2008
Location: Oklahoma
Posts: 1,185
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Yes, just drive normally, and let the car do its job...no need for the added distraction |
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03-18-2010, 01:08 PM | #6 | |
Steals terrorist's lunch
Drives: 2007 Yaris Liftback Join Date: Mar 2007
Location: Reno, Nevada, USA
Posts: 1,299
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And cycling the ignition is not a "distraction". Your eyes don't leave the road, you still have assisted steering, and the brakes are good for 4-5 touches. Seriously, of all the things that one can gripe on for being a distraction while driving, cycling the ignition is at the bottom of my list. There is a time and place for DFCO usage but it has two severe limitations: 1) It steals momentum. 2) The engine uses fuel again once any of its conditions are no longer met. Coasting with the engine off is much more efficient in all aspects when you know you'll be coming to a stop for a while, or when you want to maintain more momentum in between the times you let the engine run.
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- Brian Share the Road I often carry 2 carpool passengers and mountain bikes or snowboards/skis over a 4,500 foot elevation difference. Click the graphic above to see my detailed mileage logs. |
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03-18-2010, 02:52 PM | #7 |
Drives: 2007 Yaris LB Join Date: Mar 2007
Location: San Jose, CA, USA
Posts: 685
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The only concern that I have about roll starting the car is based on an article that I read a few years back. There is a risk for unburnt fuel to end up in the catalytic converter, where, together with a spark from the engine (since the first cat is quite close to the exhaust header) could cause a burn (mini-explosion) inside the cat. That would most likely destroy it.
Having said that, I've roll-started the Yaris a few times before and everything was fine, but I don't think I'll ever try to roll-start it when the engine is cold. Back home in Romania, when I was a kid, my dad had a crappy car and I remember the countless times we would push it down the street for half a block to start it. But that was an older car with a carburetor engine. Since most people have automatic transmissions here in the US, I always wondered, is it possible to roll start an AT car? I remember my Jeep Cherokee had a low gear (1), the only setting that would give me engine brake, but I've never tried to roll start it... I was afraid of breaking it
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5% Tint Rear | Micro Image LED Ignition Light Kit |
03-18-2010, 03:43 PM | #8 |
Half a Bubble Off Plumb
Drives: 2009 Yaris Sedan Join Date: Mar 2009
Location: Bristol, Tennessee, USA
Posts: 1,593
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No, you can't roll start an automatic.
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03-18-2010, 04:12 PM | #9 | ||
Drives: 2013 Chevy Spark 1LT 5-speed Join Date: Oct 2008
Location: Oklahoma
Posts: 1,185
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03-18-2010, 05:01 PM | #10 | |
Drives: 2008 Yaris Sedan Join Date: Feb 2010
Location: Oklahoma City, OK
Posts: 323
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http://tinyurl.com/yg2e4kz And honestly, to someone who's other car regularly gets in the 50-60 mpg range when driven normally... it seems a little silly to me to see Yaris drivers going to such lengths to go from forty-something to forty-something-point-one. -Steve |
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03-18-2010, 07:27 PM | #11 | |
Start another Oil Thread!
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save gas while slamming into the car in front of you when you have no power brakes?
yeah that sounds like a hypermiler.
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03-18-2010, 08:01 PM | #12 | |
Drives: 2008 Yaris Sedan Join Date: Feb 2010
Location: Oklahoma City, OK
Posts: 323
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-Steve * Minus a little energy lost to heat during the collision itself. |
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03-18-2010, 08:08 PM | #13 | |
Start another Oil Thread!
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i am literally rolling on the floor laughing. thank you for your perfect explanation of "conservation of energy" law.
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03-18-2010, 09:24 PM | #14 |
1NZ-6spd
Drives: '05 6-Spd Vitz RS Join Date: Oct 2008
Location: Oshawa, Ontario, Canada
Posts: 2,967
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That's not entirely true. The old 2 speed powerglide transmissions have a transmission pump on the output shaft making it possible to build enough pressure inside to spin the engine. Though I think you'd need to get it going about 20-30km/h before that would happen.
But as for the regular Auto tranny, not a chance in anything. In fact, you most you can't even flat tow because the bearings inside the transmission don't have any pressurized lubrication due to the fact that the pump is located on the input shaft. So without the engine turning you have no oil circulation and could end up with fried bearings. PS, that goes for you hypermilers out there with autos. Shut your engine off at your own risk of doing costly internal damage while trying to save a few pennies of fuel. |
03-18-2010, 09:39 PM | #15 | |
Steals terrorist's lunch
Drives: 2007 Yaris Liftback Join Date: Mar 2007
Location: Reno, Nevada, USA
Posts: 1,299
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I understand that hypermiling is different than what you know, but please do not sensationalize it. It is simply a different way to drive a car, and it works.
__________________
- Brian Share the Road I often carry 2 carpool passengers and mountain bikes or snowboards/skis over a 4,500 foot elevation difference. Click the graphic above to see my detailed mileage logs. |
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03-18-2010, 09:53 PM | #16 | |||
Drives: 2008 Yaris Sedan Join Date: Feb 2010
Location: Oklahoma City, OK
Posts: 323
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There are reasonable fuel saving practices... which are, in general, good for safety, as well. And then there are foolish practices which annoy and endanger the hypermiler and others. Fortunately, the reasonable, safe, and non-annoying ones also yield the bulk of the actual FE benefits. -Steve |
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03-18-2010, 09:55 PM | #17 | |||||
Start another Oil Thread!
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you do what you gotta do... but congratulating a guy about his ability to coast down a hill sans-power-braking is just retarded. it's not worth the ounces of fuel saved... especially considering the fact that most of you are wasting the money spent on gas...... on some other stupid obsession, like action figure collections...
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03-18-2010, 09:59 PM | #18 |
Drives: 2008 Yaris Sedan Join Date: Feb 2010
Location: Oklahoma City, OK
Posts: 323
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One thing that generally gets lost in these discussions is the true motivation. It's not the pennies worth of fuel saved. It's being able to go on forums like these and say "I finally hit 50 mpg!" and have a couple dozen people 'attaboy you for doing so well. That's the true motivation and potential pay off.
-Steve |
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