Mpg question

[turbo lover]

Coasting downhill in gear has significantly more drag and engine braking than downhill in neutral. The extra momentum gained while coasting down in neutral allows a much farther coasting distance before stepping on the accelerator again and outweighs the fuel saved through engine braking. Typically, coasting downhill in neutral is more efficient, except when brakes are needed to prevent the car from gaining too much speed in neutral.

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[Ripper3785]

Coasting downhill in gear has significantly more drag and engine braking than downhill in neutral. The extra momentum gained while coasting down in neutral allows a much farther coasting distance before stepping on the accelerator again and outweighs the fuel saved through engine braking. Typically, coasting downhill in neutral is more efficient, except when brakes are needed to prevent the car from gaining too much speed in neutral.

Interesting thoughts. It makes sense to me in a world with no speed limits and/or where the bottom of the hill transitions into a flat uninterrupted road. The hill I descend daily is a 35mph zone 1 mile long speed trap with a stoplight at the bottom and uphill afterwards. I have to use an annoying amount of brake if coasting. You only gain momentum if you are gaining speed. Your coasting distance is no different whether you are in gear or neutral if you are maintaining the same speed.

Can you cite any sources with more research on that? I believe there are cases where that makes sense. Many folks also believe being in gear is safer. Other Hypermilers turn off their ignition while coasting.

 

[Dimitron84]

Fuel flow at idle out of gear is higher than it is coasting downhill in gear(where it is nothing or almost nothing) https://www.popularmechanics.com/cars/hybrid-electric/a5977/coasting-in-neutral-fuel-economy/

(I used to do this also until I learned better)

Hmm thanks for this! Will try it

 

[turbo lover]

Interesting thoughts. It makes sense to me in a world with no speed limits and/or where the bottom of the hill transitions into a flat uninterrupted road. The hill I descend daily is a 35mph zone 1 mile long speed trap with a stoplight at the bottom and uphill afterwards. I have to use an annoying amount of brake if coasting. You only gain momentum if you are gaining speed. Your coasting distance is no different whether you are in gear or neutral if you are maintaining the same speed.

Can you cite any sources with more research on that? I believe there are cases where that makes sense. Many folks also believe being in gear is safer. Other Hypermilers turn off their ignition while coasting.

Yes, if the choice is either be in neutral and use brakes or be in gear, being in gear is usually the better choice. Less fuel consumed, more control, and less brake wear.

Most hypermilers that I know say that neutral coasting is the more efficient option in situations where brakes aren't needed. From my testing, coasting in neutral is more efficient as long as there is a flat stretch at the bottom of the hill where I can slowly bleed off the momentum while I continue to coast. Also, I can coast down much gentler slopes in neutral and maintain speed, but I'd lose a lot of speed if I tried to do the same thing in gear. If being in gear were as efficient in all situations are coasting in neutral, then hypermilers wouldn't bother with shifting to neutral and shutting off their engines. Each is another tool in the toolbox to use in a different situation.

 

[RunningHot2017]

I average between 38mpg and 45mpg in my Si. I have hit 51 before in pure highway driving. Also one thing I noticed is, the faster you drive these civics, the better the gas mileage, I get better mileage going 62mph on a moderately hilly backroad than I do going 53-55 on the same road.

 

[gtman]

Also one thing I noticed is, the faster you drive these civics, the better the gas mileage, I get better mileage going 62mph on a moderately hilly backroad than I do going 53-55 on the same road.

Totally the opposite of what happens in my CVT turbo. Hills and speed kill my mileage.

 

[WOPSiWOT]

Tracking with Fuelly for 7,154 miles. Average MPG in an Si Sedan is 33.6. Best tank was 37.4 and that was kind of an outlier. 33-35 mpg is really consistent. The internet tends to amplify the outliers and anecdotal information. I’m kind of skeptical of people that say they consistently better EPA highway ratings by 5 or 10 mpg in mixed driving, but I don’t know.

 

[syncro87]

Mid to upper 30s, mixed driving, 87 octane, on both our auto hatch and sedan turbos. I don't think we've ever seen below 33-34 on a tank no matter how hard driven or whether A/C was on, etc. Right now the computer on the sedan says 40.9 average on the current tank. Hand calc, I've found, is usually around 5% less than the trip computer.

MPG was 33-ish in winter. Big drop in cold weather.

To those seeing huge differences between the trip computer and hand calc, you're doing something wrong. If you're seeing 8 or 10 mpg better on one than the other, you're making a mistake somewhere. Miles, gallons used, etc.

Anyway, normal MPG seems to be in the 35-40 range for the turbo cars, based on a data set of two cars and two drivers. You have to try to get below 35-ish unless you're in the dead of winter.

Midwest here, so few hills. Major city, so plenty of stop lights and traffic.

Re: premium gas. I've done some pretty extensive amateur testing regarding 87 vs 91 octane gas. A number of cars, regular routes, similar driving conditions, etc. I've found there to be just about zero MPG improvement running premium gas. However, this comes with a big asterisk. * I have noticed about a 3% improvement when running non ethanol gas. Non ethanol gas is available exclusively in premium 91 grade in my area. I have run 91 with ethanol, and see no meaningful gain. If you want better MPG, the key is to get non ethanol containing gas. The octane rating alone means little to nothing in my experience. Ditch the alcohol if you want max mpg.

 

[Dimitron84]

Filled up before leaving for work then drove as careful as possible ranging from 55-80mph depending on downhill/uphill scenario and got to below within my 30 miles of highway travel.

 

[Gruber]

Tell me at what odometer you need your first brake job, and I will tell you what gas mileage you can achieve....

 

[Dimitron84]

Tell me at what odometer you need your first brake job, and I will tell you what gas mileage you can achieve....

I would imagine about 15k-20k miles on stock brakes with average driving.

 

[carsrmilife]

LOL... Those are some short lived brakes.

 

[BigDog]

'18 Si and my average MPG is 37.6 over the winter. Now that the weather is warming up I'm seeing 40+ MPG per tank with a high of 47.5 MPG on the drive back home the other day running on 87 octane gas. My round trip is around 160 miles and I've got the cruise control set at about 70 mph.

 

[brienp]

My work is 2 stoplights away. My car never even begins to register that its warm by the time I get to work. I routinely get around 25mpg just going to and from work. However, if I go on a road trip, say, up to Seattle or something, Im always over 40mpg with cruise control working. The civic seems to really like loooooong straight stretches of road with little to no change in throttle or breaking. But I guess you can say that of any mass produced internal combustion engine since most of them are only around 20% thermally efficient.

 

[JoeShades]

LOL... Those are some short lived brakes.

I have an 01 civic taht has 152,000 miles and have had the brakes done once. It is time to get them done again but I am replacing the car soon

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