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Old 02-28-2020, 09:49 AM   #1 (permalink)
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CVT's (non-hybrid) = fewer opportunities for fuel-cut mode (DFCO) when coasting?



The last CVT I spent much time driving was the 1.2L, 3-cylinder Mirage pictured above.

I was genuinely impressed by how much it was programmed to pursue fuel economy: It tries its little heart out to keep cruising revs as low as possible (see chart).

I remembered being pleasantly surprised that...

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On level roads with a light foot, you can drive around all day at sub/urban speeds under 1500 RPM, including during light acceleration.
That has me wondering: do CVT's programmed for such low RPM, fuel-saving operation offer fewer chances for zero fuel burn (DFCO) when releasing the throttle and coasting in gear? Seems possible you might only get a brief fuel cut before injection resumed to keep the engine running.

Other types of transmissions would have the engine at a higher RPM for a given road speed at the start of coasting. So, more time in fuel cut-off mode.

If that's the case, a CVT hypermiler might benefit from more neutral coasting.

Splitting hairs? Probably! These are the things that keep me awake at night.

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Old 02-28-2020, 10:43 PM   #2 (permalink)
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Funny you should mention this. I noticed shortly after buying the Versa with the CVT I never saw any indication it ever goes into DFCO. My Ultra Gauge sometimes on downhill coasts will give me readings of 175-200 MPG but even then it's constantly changing with speed and rpm. The only possible indication is in the factory installed MPG unit. It will go to 99.9 but the Ultra Gauge is just showing that it has exceeded its limits. The Scan Gauge in my Ford Escort wagon with 5 speed manual will go to 9999 as soon as I let off the gas at highway speed and stay there until either I accelerate again or the engine needs fuel to continue to operate.

With problems that have plagued the CVT I refuse to shift from "D" to "N" and back to "D" to save a couple drops of gas. If it did cause any problems with the CVT it certainly wouldn't be worth the $4000-$5000. they want to replace one.
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Old 02-28-2020, 11:19 PM   #3 (permalink)
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Doesn't seem so right that a CVT could harm the DFCO ability.
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Old 02-29-2020, 07:00 AM   #4 (permalink)
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Longevity could be the motivation behind this. Which is not to say a CVT could not be built that would last virtually forever with DFCO, but rather that it's added wear to the one component most likely to send a car to a junkyard, and people are cost-sensitive both at purchase and during repairs.
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Old 02-29-2020, 08:11 AM   #5 (permalink)
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2018 Honda CRV

Same experience as "2016 Versa"...I have a ScanGage. Immediately upon lifting my foot from the accelerator, it goes into DFCO for about 1/2 second. Then the CVT adjusts and eliminates DFCO. I am trying the EonC just for fun. Can't say it's helping enough to measure. Still getting 29-30 mpg calculated.
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Old 02-29-2020, 05:05 PM   #6 (permalink)
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Another thing I forgot to mention in my previous post the owners manual for the Versa strongly urges coming to a complete stop before shifting gears. As best as I remember the CV transmission in the Versa is non towable.
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Old 03-01-2020, 08:38 AM   #7 (permalink)
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2018 Honda CRV

Only time to be dead stopped is to shift between R and D (probably in and out of P as well). Can't flat tow the CRV at any time. Towing behind an RV can be done with the front wheel drive using a car dolly. Flat bed tow truck is the only way to tow the all wheel drive.

Edited towing...

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Old 03-01-2020, 05:37 PM   #8 (permalink)
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I watched the Ultra Gauge this morning as the car would coast down hills on the way to church. Even at higher speeds than I had the c/c set and in a full coast the best GPH reading I saw was something like .23 on a warm engine. Nowhere even close to .00.
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Old 03-02-2020, 09:12 AM   #9 (permalink)
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I'm sure the my 15 Rogue does if the hill big enough. It will ramp up the rpm when in a coast and it starts picking up speed. It doesn't do it very often because most of the hills we normally aren't big enough. But one neighboring town main street is down hills both was with the low spot in the middle and is steep enough it does it every time in a 20 mph zone if I crest the hill at that speed.

Had 4 tanks when in Colorado around at 35 mpg, it's been a while but I think the CVT would ramp up to either 3400 or 4300 rpm going down hills to avoid brake use. Car's ahead of me were braking a lot more than I seemed to need to.
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Old 03-02-2020, 11:40 AM   #10 (permalink)
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From my personal anecdotal perspective, my wife is a decent eco-driver, though certainly not as obsessed with it as I am. She manages in the high 30's and low 40's consistently with her CVT Honda Fit. So while a CVT might be less effective in the hands of a dedicated eco-driver, perhaps in the hands of someone who is merely trying to do well without extricating every last tenth of an MPG, it serves them better than a "normal" transmission would.

Also of note, my dad is decidedly not an eco-driver. I watched him consistently slip my Yaris (manual transmission) out of gear to decelerate and use only the brakes. For someone like him that doesn't utilize DFCO at all, a CVT's lack of it would have no noticeable effect on his fuel economy, and with its optimized shifting and torque distribution map might help him achieve higher numbers.

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