Effect of coasting in Neutral on MPG display

[mpaton]

I've read comments from people who coast about this affecting the MPG display.

So here's some more pertinent information. Today I drove up a somewhat twisty road towards a ski area. The road had a 35mph speed limit, and was generally uphill. On the way back down, I started coasting in Neutral (manual transmission) with the engine still on, and reset the A Display while moving. I did this before while driving down a hill at about 60mph, and the display promptly went to ---- for a few seconds, and then read 61.0 MPG

This time, it went to ----, which didn't really surprise me, but I was surprised when it stayed like that for about a mile. By then, I had encountered a slight uphill stretch, and my speed had slowed to about 28mph, so I engaged 5th gear, accelerated gently back to just over 35, and then put the gear lever back in neutral, thinking this would then produce a reading. But no, no reading for the next half mile, until I stopped at a Stop sign, and then pulled away.

So maybe some more experiments along these lines will tell us how the consumption is calculated, possibly being useful to the frequent coasters.

[BillThompsonMirage-ES-CVT]

I have a 2015 ES with CVT. My observation is that when coasting in N, the MPG reading is ---.

[wellswebdesign]

I have a Scangauge E and a manual transmission. It gives a fairly instantaneous mpg readings. I think it basically shows what the last few seconds mpg rating is. When coasting in neutral, the highest "real" number I've seen is around 250mpg. It often just goes to 9999mpg. I don't coast enough to know how much it helps the overall mpg, but I do know it coasts quite nicely!

[Don]

Hi Wellswebdesign,

What has the Scangauge showed you so far. I have the 5 speed too, would love to know what the sweet spot is MPH and rpm for the little 3 cylinder. and is the rpm sweet spot ruffly the same in all gears...I have never seen a Scangauge in action, only on web video so i don't know to much about them other than they are supposed to be good for instant information to help with MPG.

I got this on a 12 mile round trip to town and back for my AVG MPG, was 68 going to town and came down to 65 on the way back. I am really wanting to work on upping the mpg while the engine is on and im driving so that i can keep increasing it over all.

Thanks in advance.
Don

[MetroMPG]

If by sweet spot you mean "best fuel economy", it's the same rule of thumb as any other car I've driven: the lowest speed in the highest gear possible/practical.

FYI, see:
Thread: Speed vs. mpg/mileage/fuel economy chart - Mirage 1.2L 5-spd and CVT

[Don]

Thanks Metro,

I have a copy of that chart in my car. I am wondering about Scangauge and how it can help as far as getting to the wanted speed. I tend to really speed up slow and I know that it is possible that i do this to slow and wasting energy by accelerating to slow to get up to speed I am usually in 5th by about 25 to 30 mph. when trying to get to 60 so i can coast down to 40. LOL i know it is a crazy question. but i am thinking some others might be a bit crazy too and know the ruff answer. I am disabled and doing the mpg competition against myself is a blast.

Thanks in advance, Don

[MetroMPG]

So you're mainly wondering about acceleration technique. There's no simple answer, but lots of "it depends..." situations.

Glacial acceleration (like 0-60 mph in a minute) isn't great: the engine is inefficient accelerating at extremely light loads.

Fast acceleration that uses high RPM isn't good either -- high RPM is very inefficient.

Strong acceleration that uses high load, but low RPM (requires a manual transmission, shifting at no more than ~2-3k RPM), is more efficient, particularly if it's followed by a long coast (look up "pluse and glide").

One instance where slow acceleration is more efficient than the above is if you have to slow down again immediately after accelerating.

I've spent a fair amount of time coaching people to drive efficiently, and it's common for people to worry about acceleration technique. But the truth is it doesn't matter as much as what acceleration technique you use as what you do AFTER you accelerate. People waste far more fuel with the brake pedal than the gas ... by failing to react early to slowdowns ahead by rushing in and jamming on the brakes at the last minute instead of easing off the gas early and coasting in.

[Daox]

When I had my test Mirage with the CVT, I found that if you had a steady foot, this was the best way to accelerate. Push the gas pedal down however much you want, and keep your foot there. This kept RPMs lower and engine load higher. If you constantly kept moving the gas pedal, the car kepts RPMs higher not knowing if you'll want more power or not.

[Don]

Thanks Metro,

The Strong acceleration up to 2 to 3k rpm before shifting makes sense and is what i wanted to know...for around here there are so many hills that are close, especially on the back roads that sometimes it is hard to get back up to speed before it is coasting time again. I think that technique will get me there.

Yesterday i did something like this going to town and was able to get 68 mpgs in about 6 miles. return trip i got 65. I did almost all engine off coasting and think i can do it better using that technique. It will allow me to go engine off several seconds sooner each time and that is where the huge savings is. Once i get the timing down on this car i will use more engine on coasting.

Thanks again, you answered just what i was wanting to know.

thanks for reading, Don

[Don]

thanks Daox,

that makes sense, with the manual 5 speed i think it works great too, on fairly level roads. When i get to the mpg i want on the avg read out i find doing that the best way to hold it close to that avg.

thanks, Don