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

[Ratbert]

Didn’t someone post here before that ran his city commute for 6 months on, then 6 months off, and only saved around a couple gallons of gas?

I noticed the pic above showed the fuel for idling 3.6 minutes vs one restart. I don’t know of any stoplights that make you wait that long, so IMHO that isn’t a good comparison. Show the fuel usage for a typical time of a red light. It would be much more accurate.

3.6 minutes was the average for how long the surveyed people thought it would take for it to be beneficial. The two vials showed how far off their estimates were from reality.

Based on their tests the break even point was seven seconds, not 3.6 minutes.

Consider watching the video before giving your humble opinion on how it should have been done differently.

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[Fatbob Frank]

I don't care how much gas it saves... it's annoying AF...

 

[AFD]

I don't care how much gas it saves... it's annoying AF...

Not at all, once you train yourself to press the disable button immediately after every start-up.

But then one day you forget and somehow make it to your destination without triggering it once - until you come to a stop when parking and the engine shuts off and then needs to immediately restart just so you can put it in park and shut it back off again.

 

[2nd 392]

S/S does indeed save fuel, especially in heavy red light prone city driving.

That being said, it was primarily designed to cheat the EPA city MPG testing. This is done as roughly ~34% of the test is spent idling. The system needed to be automatic before the EPA would certify it as legit, so here we are.

What the engineers failed to realize is the wear and tear it would put on batteries. They thought about the starter, at least. Most heavy S/S users end up replacing their batteries every 2 years at most. Very few make it 3 years. Compare that to a conventional system where a battery can last 5-7 on average. The additional maintenance cost most likely outweighs any fuel savings, especially now that you're paying for two batteries. If you're paying someone else to install them for you I don't think it's possible to even break even there. There's also the increased chance of being stranded from a dead battery no-start.

This also led to the hilariously incompetent clutch situation on the manual JLs. Had to be light enough for S/S to function, and ended up being weak garbage as a result. I wonder how much cheaper it would've been to pay EPA fines instead of releasing 3 different recalls for clutch failures.

Thank You- this is not only an excellent explanation of S/S, but also an explanation of why the V8 nearly achieves the EPA 17 mpg hwy number, but their 13 city is 1 1/2- 2 high with effort, worse without. It’s how they test for the numbers.

 

[NWJeepr]

S/S does indeed save fuel, especially in heavy red light prone city driving.

That being said, it was primarily designed to cheat the EPA city MPG testing. This is done as roughly ~34% of the test is spent idling. The system needed to be automatic before the EPA would certify it as legit, so here we are.

What the engineers failed to realize is the wear and tear it would put on batteries. They thought about the starter, at least. Most heavy S/S users end up replacing their batteries every 2 years at most. Very few make it 3 years. Compare that to a conventional system where a battery can last 5-7 on average. The additional maintenance cost most likely outweighs any fuel savings, especially now that you're paying for two batteries. If you're paying someone else to install them for you I don't think it's possible to even break even there. There's also the increased chance of being stranded from a dead battery no-start.

This also led to the hilariously incompetent clutch situation on the manual JLs. Had to be light enough for S/S to function, and ended up being weak garbage as a result. I wonder how much cheaper it would've been to pay EPA fines instead of releasing 3 different recalls for clutch failures.

The Europeans were using stop-start systems long before it became a feature in cars destined for the US so I call BS on your assertion that it was designed to cheat EPA tests. A break even point of 7 seconds per a post above seems to indicate there is some fuel savings. In a fleet average that is significant.

The JL’s two-battery design is unfortunate. But that seems unique to the JL as we’ve owned other vehicles with the feature and they only had one battery… and battery life was definitely not shortened noticeably, as that cars battery was still strong at 5 years.

 

[Fatbob Frank]

Not at all, once you train yourself to press the disable button immediately after every start-up.

But then one day you forget and somehow make it to your destination without triggering it once - until you come to a stop when parking and the engine shuts off and then needs to immediately restart just so you can put it in park and shut it back off again.

I feel your pain...

 

[AFD]

Thank You- this is not only an excellent explanation of S/S, but also an explanation of why the V8 nearly achieves the EPA 17 mpg hwy number, but their 13 city is 1 1/2- 2 high with effort, worse without. It’s how they test for the numbers.

Tldr; but if I had a 392, I'd be real proud of my shitty fuel-economy and might even rev my engine at a stop light now and then.

The other gas Jeep engines are really nothing to brag about by any metric

 

[2nd 392]

Tldr; but if I had a 392, I'd be real proud of my shitty fuel-economy and might even rev my engine at a stop light now and then.

The other gas Jeep engines are really nothing to brag about by any metric

Yeah- OR+ and a playful foot in town gets it into the 9’s

I have friends that spend their fun money on golf, or season tickets and related expenses, one takes a 2 week exotic vacation and another week “just” to Hawaii every year. My extra fun money gas is much cheaper. And enjoyed daily.

 

[Y2KFirehawk]

EPA Chief: Auto Start/Stop Technology Is Done

 

[2nd 392]

EPA Chief: Auto Start/Stop Technology Is Done

 

[BMCGC]

My F150 3.5EB gets about 22 mpg with ASS. About the best I ever saw with a pre-2010 full size truck was 15 mpg. I find it annoying myself.

 

[Terrymo]

3.6 minutes was the average for how long the surveyed people thought it would take for it to be beneficial. The two vials showed how far off their estimates were from reality.

Based on their tests the break even point was seven seconds, not 3.6 minutes.

Consider watching the video before giving your humble opinion on how it should have been done differently.

Busted…I didn’t really watch it either…just skimmed it

 

[GabeBoyTheGreat]

Well technically, the ASS system doesn't save any fuel at all. Shutting off the engine instead of idling will save you fuel, but you don't need a complicated ASS system to do that.

If you know you are going to be sitting idling for an extended period of time, you have the ability to turn the ignition off/on yourself. It is way to more effective to do this yourself than to make the vehicle heavier/more complicated by implementing an ASS system.

ASS is absolutely a way to cheat the EPA regulations, because like I said, in a real world scenario, it is more effective to shut the ignition off manually than to rely on ASS all the time.

When I forget to turn my ASS off, 90% of the time, the vehicle shuts off for less than 7 seconds, which means my ASS is actually burning more fuel than it is saving during the 10% of the time that it exceeds 7 seconds. Additionally, in the middle of the summer, that number jumps to about 99% because the vehicle is trying to keep the cabin cool.

So yea, the real world benefits are nonexistent. The only way to actually save fuel is to manually shut the vehicle off when you know you will be sitting for a while. I do this sometimes when I am stopped at local traffic lights that I know have long cycles.

 

[NWJeepr]

Wait until gas gets really expensive again (because it will) and the same people will be in here bitching and moaning about how expensive it is and how they can’t afford to drive their Jeeps to work and they have to decide to buy groceries or get gas but can’t do both! Lol

 

[Valpo Jeep]

If I was worried about saving a little bit of fuel then I would not be driving our Wrangler or our Maserati.

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