My Prius, The Fair Weather Car, ECO Mode or Normal ?

Not counting cabin comforts, I am finding that the MPG is largely unaffected by which mode you're in - if there's a difference (for normal drivers), it's less than 1mpg. The computer is smart and the total amount of energy required to get up to speed is nearly the same whether you do it quickly or slowly. Other factors like top speed and outside air temp are far more significant factors.

That said, hypermilers will get more from ECO in stop&go traffic in colder temps because it shuts off the gas engine sooner.

 

Hmmm, I'm still out on this one. Sometimes I'm sure the car is better in Eco and other times I'm not. I usually use eco in start stop town traffic and normal mode on a long run, with power used when overtaking.

 

eco mode reduces throttle response. so in general, it can help your mileage, but only because we as a species are not always diligent in our actions.

this prevents the car from accelerating more than intended in normal driving situations. the true power level is still the same and at a certain point on the accelerator pedal the mode is overridden. iow, if you need full power, it is still there no matter what mode you are in.

as for me, i am always in eco mode because this allows me to daydream about other things; EV's, domestically produced power, winning lottery tickets...

 

one way trips usually dont work.

changes in elevation, wind speed and direction, etc... all will play a part.

best bet is to take a regularly driven route (a work commute is best if long enough)

track results over time. add to it temps, etc. any notes for unusual traffic conditions etc. do at least 10 on each then post results...

 

You also should realize that your mileage will improve over time as the ICE and other components break in. Some believe this takes as long as 10k miles on the Gen 2.

 

Here's the deal: If you had to move 200 bricks up a flight of stairs, it takes the same amount of energy (total) to move them one at a time, or all at once. But it takes more power to move them more quickly.

The amount of energy it takes to get the Prius up to speed is the same whether you get there slowly or quickly. But the ICE has a "sweet spot" for power output, so it is more efficient when accellerating in the sweet spot rather than when it is above - or below - that range.

To put it another way, when you floor it, you're getting rapid accelleration but the engine is beyond the sweet spot for efficiency, so the energy produced "costs" more than if you took your time and stayed in the sweet spot.

But the same thing happens BELOW the sweet spot (assuming you're not drawing surplus from the battery - which, as others have pointed out, is usually an expensive source to draw from). Grunting along trying to creep up to speed is just as wasteful because the engine is outside of the optimum range.

I think what happens with PWR mode (vs ECO) is that you're more likely to spend time in the sweet spot rather than below it. You might lose some efficiency by overshooting sometimes, but it probably nets out the same overall (unless you overshoot a lot).

It depends on what kind of driving you do, but I think for most zones above 25mph, without lots of stops, PWR mode is likely to be more efficient. I know it's more "normal" compared to the way other drivers accellerate, and more "fun".

 

all that is true and if devoting 100% of your attention to the traffic, road conditions, etc... it would not matter what mode you were in, the results would be the same.

now, in eco mode, it simply prevents you from pushing the accelerator just a teeny bit too much and accelerating faster than you really need to which is easily to do if the car is very responsive. with the pedal dampening effect of eco mode, its easy to subtly apply more pedal pressure if more response is needed. it take a lot of due diligence to avoid pushing too hard ALL the time.

in the stairs example, neither one brick or all the bricks on a trip is the best option. probably something like 10 bricks per trip is best. and yes, no matter how you get them up there, the amount of work is the same but..

try running up with a load and see how long it takes before you cannot run anymore. you will find that even with rests between trips, you will be much more tired. slow and steady insures that the job is done without overtaxing yourself.

your Pri is not much different.

 

Yes, but too slow and you're below the engine's sweet spot - and being inefficient.

Without a tachometer, I can't say exactly where on the HSI the sweet spot begins and ends, but I suspect the starting point is very high in the white area and extends well beyond the power zone. Staying below that range might make the "ECO" light appear, but it's actually less efficient.

 

no... that would be making 200 trips carrying one brick at a time... i am doing 20 trips, 10 bricks.

 

Tom, just curious if you have seen the efficiency diagram Ken@Japan posted for our engine?

 

That's exactly what I'm referring to - does anyone know how (or if) that maps on the HSI? (and I mean for-real, not speculation)

 

I have a SGII and will print out the mapping and see how things land. I would have to believe that the HSI takes into account more than the ICE though.

 

Not to mention that driving in ECO mode makes your new Prius respond like a 1985 Yugo with an oil leak.

 

Were there any that didn't have an oil leak? :madgrin:

 

ECO mode in winter will prevent, on a broader range of conditions, the ICE to run when stopping at a light, to keep the cabin interior warm (not mentioned on the user's manual, among other things...). The fan will also run slower - like mentioned in the user's manual.

I still don't believe that ECO and PWR mode simply change the mapping of the gas pedal.
In ECO I get the distinct feeling that when I press the gas pedal to get, say, half PWR-red region full in the HSI, I am not getting the same response in acceleration, as when I reach the same region in PWR mode.
Or better, I think that if the same amount of "acceleration press" on the HSI is shown and is achieved on 2 different gas pedal positions, the engine and the motor are still managed differently. For me the 2 modes instate 2 different engine management routines.
Say, more current allowed to the motor, or different more power optimised VVT timing compared to more sparingly timing in ECO, even when the acceleration applied is the same (with 2 different gas pedal positions).
Otherwise the HSI is showing, for example, full power area, when in fact the throttle is in 2 different places when in ECO and PWR mode. That is, the HSI is not showing the same amounts of gas applied in the 2 modes.

Does this make sense?

Again, I don't believe the modes simply change the mapping of the accelerator to the position of the foot. There is a bit more going on and we don't know yet what it is. Don't you think? Even the engine makes a different noise when PWR mode is set and you are accelerating with the same bar length in the HSI indicator is shown...!