How much fuel does ASS (Auto Start Stop) save?

[AndySpill]

I fully realize that this thread seeks to measure how much fuel engine start stop systems save.

Answers here are expected in measures of volume and time. In other words “you'll save x milliliters of fuel for every z seconds the engine is off, but consume y milliliters of fuel you wouldn't have to to restart the engine, such that after this many seconds after some threshold with the engine off, you'll save this much “dinosaur juice” per minute."

It doesn't seek to factor in the cost of more wear and tear on batteries or moving parts, or even the additional environment footprint of equipping and replacing such components sooner, that only fairly needs to be offset against the air pollution and greenhouse gas savings that engine start stop systems save us from. And these engine start/stop systems do definitely save appreciable amounts of fuel across all the vehicles with this technology, if not whopping large amounts at that.

And yet, interesting topic though it is, IMHO none of this really gets at the heart of the matter of what is attempted to be achieved by such engine stop systems, much that you're free to believe/disbelieve that the goal is attainable or necessary/good, or that if good intentions are even the case here, that such policy is well written, flawed, or somewhere in between. (IMHO there are many flaws with the EPA rules that qualify a vehicle for the more favorable gas mileage ratings of such systems. Case in point, how many JL owner's ESS system stopped working about a month after ownership?)

At their heart, the CAFE standards that motivate engine start stop systems seek to raise the market cost of ICE vehicles more and more over time, which in theory makes electric ones, relatively speaking, less expensive, such that people in turn buy them in the larger quantities, that again in theory (and yes, somewhat in practice) lower the cost of electric propulsion's purchase price, through innovation and economies of scale.

And do electric vehicles themselves have a tail pipe, if not literally in the back of the vehicle, then in the green footprint of their manufacture, how their electric is created, and ultimate demise after years of use: you bet.

Sometimes it almost feels like we are, rather than solving environmental problems, replacing ones seen as more urgent (fossil fuel emissions) for ones that right now are less pressing (burying unusable old battery components in the ground and polluting land) but that may no less come to "bite us in the ass" down the line.

My $0.02, off soapbox.

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[alphawolff]

Sometimes it almost feels like we are, rather than solving environmental problems, replacing ones seen as more urgent (fossil fuel emissions) for ones that right now are less pressing (burying unusable old battery components in the ground and polluting land) but that may no less come to "bite us in the ass" down the line.

My $0.02, off soapbox.

My favorite is the picture of a Tesla supercharger station being powered by a diesel generator.

 

[Mothman]

Can someone save me 7 minutes and just tell us how much fuel it saves, and what this guy’s credentials are?

I heard he worked on Volkswagen mpg #’s

so there’s that

 

[Mothman]

I fully realize that this thread seeks to measure how much fuel engine start stop systems save.

Answers here are expected in measures of volume and time. In other words “you'll save x milliliters of fuel for every z seconds the engine is off, but consume y milliliters of fuel you wouldn't have to to restart the engine, such that after this many seconds after some threshold with the engine off, you'll save this much “dinosaur juice” per minute."

It doesn't seek to factor in the cost of more wear and tear on batteries or moving parts, or even the additional environment footprint of equipping and replacing such components sooner, that only fairly needs to be offset against the air pollution and greenhouse gas savings that engine start stop systems save us from. And these engine start/stop systems do definitely save appreciable amounts of fuel across all the vehicles with this technology, if not whopping large amounts at that.

And yet, interesting topic though it is, IMHO none of this really gets at the heart of the matter of what is attempted to be achieved by such engine stop systems, much that you're free to believe/disbelieve that the goal is attainable or necessary/good, or that if good intentions are even the case here, that such policy is well written, flawed, or somewhere in between. (IMHO there are many flaws with the EPA rules that qualify a vehicle for the more favorable gas mileage ratings of such systems. Case in point, how many JL owner's ESS system stopped working about a month after ownership?)

At their heart, the CAFE standards that motivate engine start stop systems seek to raise the market cost of ICE vehicles more and more over time, which in theory makes electric ones, relatively speaking, less expensive, such that people in turn buy them in the larger quantities, that again in theory (and yes, somewhat in practice) lower the cost of electric propulsion's purchase price, through innovation and economies of scale.

And do electric vehicles themselves have a tail pipe, if not literally in the back of the vehicle, then in the green footprint of their manufacture, how their electric is created, and ultimate demise after years of use: you bet.

Sometimes it almost feels like we are, rather than solving environmental problems, replacing ones seen as more urgent (fossil fuel emissions) for ones that right now are less pressing (burying unusable old battery components in the ground and polluting land) but that may no less come to "bite us in the ass" down the line.

My $0.02, off soapbox.

You pretty much nailed it

it’s useless

it’s expensive

nobody wanted it

 

[NWJeepr]

Sometimes it almost feels like we are, rather than solving environmental problems, replacing ones seen as more urgent (fossil fuel emissions) for ones that right now are less pressing (burying unusable old battery components in the ground and polluting land) but that may no less come to "bite us in the ass" down the line.

My $0.02, off soapbox.

There is impact in everything that mankind does to the environment around us. The goal is to sustain it so it continues to support the kind of abundant life we seek.

EV's aren't without environmental challenges. But even the best gasoline engines on the market are only about 50% efficient...the rest of the energy is lost to heat and sound. ICE are about as efficient as we can make them without increasing the price of those engines well beyond affordability in a passenger vehicle.

At some point it just makes sense to diversify our energy sources and propulsion methods and to spread out the impact in different ways.

 

[NWJeepr]

Just to be clear, *all* emission and fuel saving devices are because of EPA (or EU) targets. OEMs don't go out of their way to increase the price of their vehicle while decreasing reliability for shits and giggles. As with all things is a cost equation, and they figured the EPA benefits outweighed possible reliability/warranty cost concerns. They were obviously incorrect in that regard.

All fun and games until your vehicle doesn't restart at a red light and you tow it to a dealer to get a $1000 bill, assuming you didn't cause an accident.

Actually and literally, automakers included it in their vehicles for monetary credits. This is little more than a cost saving measure because the proposal is to eliminate the credit to automakers. It just happens to also be a dog whistle to some fervent supporters, why waste a good opportunity.

Stop/start systems aren't unreliable in general. Jeeps with the dual batteries are an aberration. And if you want to eliminate complexity...get rid of ICE. EV's are so much simpler.

 

[c20040215]

Well, the Engineering Explained video says the breakeven point is about 7 seconds, correct? I realize it is a different engine being tested, but let's assume it is AROUND 7 seconds.

If i leave my ASS on, most of the engine shutoffs will be right around 7 seconds or less. Therefore, most of the ASS stops are wasting more fuel than they are saving.

On the contrary, if I manually shut off the engine when I anticipate the stop to be at least, say, 30 seconds, then that means ALL of my engine shutoffs will result is less fuel wasted.

For context if it helps, I do not live in a city. ASS usually kicks in at stop signs, parking lots, or stopping to turn onto another street. When I shut the engine off manually, it is usually at lights where the cycles are 1 minute or longer.

You manually shut off the engine is different than the ESS shuts off the engine. I know It sounds weird the engine is off in both scenarios but in different ways.

I think your logic works but you can turn on the ESS when you know you have a long start, let the system work. Instead of manually turn off the Jeep.

 

[GabeBoyTheGreat]

I think your logic works but you can turn on the ESS when you know you have a long start, let the system work. Instead of manually turn off the Jeep.

This is basically how I treat my ASS; turn it on ONLY when I know I have a long stop. However, this kind of defeats the original intent of ASS.

Additionally, my Camaro has no ASS, but I still practice shutting off the engine during long stops. So to me, ASS is pointless.

 

[Dusty Dude]

Under what situations does it consume more fuel? About the only scenario I can think of would be a stretch of empty road with lots of stop signs with no competing traffic.

Rush hour traffic in Chicago on the Kennedy, Edens, or Dan Ryan expressways. Or LA, New York, etc. Pick any major city with backups.

 

[2nd 392]

Rush hour traffic in Chicago on the Kennedy, Edens, or Dan Ryan expressways. Or LA, New York, etc. Pick any major city with backups.

I can’t imagine having a vehicle in which you cannot disable S/S in the stop and crawl every few seconds LA traffic. My left clutch leg hurts just remembering countless hours of it in the big rig. Edit- maybe ok with e-torque ?

 

[alphawolff]

I can’t imagine having a vehicle in which you cannot disable S/S in the stop and crawl every few seconds LA traffic. My left clutch leg hurts just remembering countless hours of it in the big rig. Edit- maybe ok with e-torque ?

Usually the vehicle will need to reach a speed threshold (18mph?) after a stop/start even before it can trigger again specifically for stuff like that

 

[variableknife]

Am I the only one who is channeling their inner Eric Cartman from South Park with the whole ASS saving gas topic?

 

[Brad Hearing]

It's a bit surprising how much it saves. City driving, of course. And he doesn't take additional wear into consideration.

if you dont consider any other factor like wear then yeah, its obviously going to be more better-er.

 

[Badunit]

Lets say my commute to work is 20 miles + 3 minutes of idling at stop lights and I average 15mpg with auto-stop-start off:

20/15 = 1.3333 gal for the entire trip, including idling.
Idling = 0.0055 gal/min (I doubled the rate given in the video and ignored the start-up fuel)
For 3 minutes idling, auto-start-stop would have saved me = 3 * 0.0055 = 0.0165 gal

With auto-start-stop my mpg would be 20/(1.3333-0.0165) = 15.19 mpg which is a gain of 0.19mpg and I would have saved 0.0165 gal * $3/gal = 5 cents. So auto-stop-start would save me 5 cents on my commute (50 cents/wk, both directions) while simultaneously annoying the living hell out of me. Excuse me if I am not jumping up and down with joy.

 

[jadmt]

I think even the split second delay when accelerating can be a hazard. Rolling the dice on a restart is scary.

100% why I cringe when I see motorcyclists at stop lights with their bikes in neutral and hands off the bars.....I would cringe at jeeps with manual drivers doing the same thing.....nothing like sitting at a light and hearing the screeching of brakes behind you......

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