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2020 Limited
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Discussion Starter #1
I’ve been using auto start stop all the time. So far it says I have saved about 5 gallons over the roughly 7000 miles I’ve been using auto start stop. I’ve noticed however that my mpg noted on the dash is overestimated and that the amount of overestimation varies. When I use an app like Fuelly to document my actual mpg, my cars dash overestimates it by about 1-1.5 mpg. I wonder if someone who doesn’t use auto start stop can let me know if their mpg varies also. I’m thinking the reason it varies is probably because auto start stop thinks its saving fuel but it’s actually not.
 

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2020 Limited
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Discussion Starter #2
Note: when using auto startup stop the cars mpg on the display does not change when the car is stopped. Confirmed this when resetting Trips and the trip mpg will vary widely since there are only a few miles at the time but not whenever auto start stop is in use
 

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20 Outback Premium
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Our 19 did not have start/stop and overestimated the mileage by about 5%, the same as our 20. Fuelly average on our 19 after 19000 miles was 30, after 11,000 miles on our 20 is 31. Those are good numbers and mirror the epa estimate of 1mpg higher for the 20 over the 19.
 

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2020 OB Limited, Titanium & Magnetite Grays
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2.5L, consistently seeing 3% higher mpg on the dash than when I calculate the mpg. When driving on city streets and short distances the S/S has a bigger impact. Previous car always showed a concerning drop in mpg when stopped on the trip back from fueling up. We always have one long left turn stop where the mpg rapidly dropped, but now it is gone with the S/S.
Concerns about the S/S is earlier mechanical/electrical failure of the starting system and the related issue of an expensive but unreliable LN2 battery. I also dislike the designed excessive effort to turn off the S/S; maybe turned it off once but I want the easy option especially when monitoring the battery charging.
With very conservative combined, more highway, driving I am seeing may be 28 mpg.
 

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2019 Ascent Touring (me) 2016 Outback 2.5i Limited with EyeSight (Spouse's Vehicle) 2011 Outback 2.5i Limited (daughter's ride)
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The primary fuel savings advantage for Start/Stop is for the fleet average for the manufacturer which has significant financial impact on their business. End users will get some benefit, but it will be marginal in money/fuel saved.
 

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2020 Outback Limited Abyss Blue Pearl 2.5
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I leased my last Outback, so I didn't worry too much about it. I'm keeping my new 2020 so I'm more concerned about it's well being. I have no use for the auto Start /Stop, and would rather use a tiny amount more fuel, than have additional wear on the starting system. the 2nd thing I always do after starting the engine is kill the S/S.
 

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2020 OB Limited, Titanium & Magnetite Grays
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The primary fuel savings advantage for Start/Stop is for the fleet average for the manufacturer which has significant financial impact on their business. End users will get some benefit, but it will be marginal in money/fuel saved.
So where is it required or documented that the S/S off switch be buried 3 levels in the options to get credit? I am attempting to determine if it is a government or Subaru mandated obstacle and where the source of the answer can be verified. Depending on the answer, I may want to vote someone out of office.

On the other side, I am thinking about conditions where I would always turn off the S/S. Do the following conditions fit the decision?
  1. Driving a short distance to the store where engine fails to heatup enough to activate S/S. On (default)
  2. On a roadtrip where there is mostly highway driving with rest stops at 2-4 hours: On
  3. Driving a series of short trips avering 3-7 miles on city streets (salesman). Defaults many times: Off
  4. Driving to work with 3 miles of city streets plus 12 miles of highway with a little stop and go traffic: On?
 

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Please don’t work too hard on the question of who is “requiring” auto S/S and/or made the decision to put it on various models.

The simple and correct answer is the manufacturer. Not the government, which establishes fleet mileage requirements but not the methods to achieve them. Nor does the government decide whether to employ a “one time” off switch for S/S or that it defaults “on” after every stop. Again, that is Subaru. The EPA mileage, however, if measured with auto S/S on, is reduced if the device can be permanently defeated. Which is why most of them are default on.

So vote Subaru out, if auto S/S is a problem.
 

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2019 Ascent Touring (me) 2016 Outback 2.5i Limited with EyeSight (Spouse's Vehicle) 2011 Outback 2.5i Limited (daughter's ride)
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So vote Subaru out, if auto S/S is a problem.
You'd have to do the same with almost every other manufacturer, although not on every model. Yet...
 

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2014 2.5i Limited - waiting on 2020 Onyx XT
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The simple and correct answer is the manufacturer. Not the government, which establishes fleet mileage requirements but not the methods to achieve them.
I'm not 100% sure, but as part of my job I interact with automotive engineers and believe you are wrong.
What you are saying is true in the sense that manufacturers do have fleet mpg requirements, and many opt to meet them by having all kinds of little tricks, as opposed to taking more weight or horsepower out, which would impact sales worse than having these features.

On the other hand, there are indeed specified benefits for technologies designed for the sole purpose of fuel economy. Like start stop, and the grills that open and close depending on speed, etc. If on average a feature saves, say, 0.1 mpg, the manufacturer gets credit for far more than that by having it, because its sole purpose is improvement in mileage. This is how fleet averages can officially be far beyond what we all know they actually are. I think there is even a list of them of which start/stop is included.

There's also the game of getting it to qualify as a truck. Truck requirements are lesser. So, big cars are no longer. If you designed a large car, you need to increase its curb weight and thus lower its mileage so that it can be called a truck, and a small truck brings up your truck's fleet mpg average as opposed to a large car bringing down your car fleets mpg average. This is why full sized sedans are rare but crossovers proliferate.

In the end, yes, the manufacturer chooses it, it's not expressly required like some safety features are. But they are incentivized heavily to do it. Either do these or make a crappy car nobody wants. Saying its not a result of government regulation is missing the forest for the trees.

That's not a stance for or against. It's just wanting it to be clear that yes, the government has steered the direction of automobile engineering to a very high degree.
 

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2014 2.5i Limited - waiting on 2020 Onyx XT
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They go together
Fyi, if the stop is less than about 10 seconds, it's actually worse for both emissions (NOx and others included when they talk about car emissions) as well as CO2 (which is not included in "emissions").

That breakeven time is different for different vehicles, but 10 seconds is about average. For less than 10 seconds, idling causes less emissions and CO2. For more than 10 seconds, it does what its supposed to.
 

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2020 Outback Limited
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Our 18 Forester w/o SS and our 20 Outback w/ SS both overestimate about the same. 1 to 1.5 MPG. We’re averaging about 30 actual in the Outback. 28 city, 32 hwy, with conservative driving.
I track my mileage on Fuelly for all my cars, and every one of them has always been a bit optimistic with the dash display vs the hand calculation in Fuelly. The only car that was dead nuts on was my 2014 BMW 320i. It was always within a few tenths + or - of my hand calculations. Every other car has been 1-2 MPG higher on the car display than actual.

I have yet to fill up my 2020 Outback since I got it, so I don't know how it'll fare when I finally do :)
 

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2019 Subaru Forester Premium, Crystal Black Silica, Pkg 15
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I used to be a big fan of the auto start stop with my 2019 Forester I’ve had it active for over 12 hours but have been turning it off.

It is quite an annoyance in suburban driving when it activates at stop signs. I like to drive with auto vehicle hold activated so it will activate as soon as it hits 0 mph.

Fortunately for me, the Forester has a physical button near the rear gate memory button so it is very quick to disable.

The starter and the battery are more robust and purpose built so I don’t think they will burn out early but will probably be expensive to replace.

My data suggests I save around 3 mpg when it’s enabled. I drive mostly city in an urban commute. I’m running about 20 mpg city without it according to Fuelly.

The more “city” you drive and the more it activates, the more fuel you will save. (And, potentially, the faster your components can wear out...)
 

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2020 Outback Touring XT, in Crystal White Pearl
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I've been recording my mileage since getting my 2020 OB (Touring XT), and the manual calculation has been averaging about 0.5 mpg worse than what the car's trip computer reports. On a per-tank basis, the range of "error" has been from -0.1 (manual calculated value was actually a bit better than the trip computer), to around 0.8 mpg worse. Reasonably accurate. The vast majority of my fill-ups are at one Costco gas station, different pumps, of course. And I always let it click off automatically, with no extra "topping off".

My wife's 2018 Honda Accord Hybrid is interesting, in that it's trip computer always reports worse mileage than the manual calculation, and the delta is pretty consistently 2.5 - 3.0 mpg. For example, the manual calculation will be 47 mpg, and the trip computer will only report 44. I suppose it's good that the reality is better than the reported number, but I still wish the trip computer was more accurate, and "did the car justice", so to speak....

The range on that car is always over 500 miles, and sometimes pushes 600 miles, even with a 12.8 gallon tank....
 

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2020 OB Limited, Titanium & Magnetite Grays
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The Outback displayed can be adjusted. I recall the increments are 5% and the dealer can do the adjustment. If it is off by 3-7% (inclusive) I chose to adjust by one increment (5%).
 
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