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

[Ratbert]

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

In the past 62,000 miles, auto stop start has saved me approximately 15 oz. of diesel fuel. It almost always displays "Auto Stop Start Not Ready" or "Battery Charging".

There's something wrong with that part of your electrical system. Have you checked your IBS?

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[Ratbert]

My mother in laws wagoneer died at a red light because the start stop was active and the battery was bad.

That's a bit challenging to believe on face value. These things disable themselves whenever the stars aren't perfectly aligned, yet it kicked in when the battery was so bad that it couldn't start the Jeep again?

 

[alphawolff]

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.

It was designed to cheat EU testing as well. EU goes even more crazy due to their fining system. It's why they have 20k mile oil change intervals. At least we're not at that level of insanity.

 

[calemasters]

There's something wrong with that part of your electrical system. Have you checked your IBS?

I have replaced the IBS and both batteries. I am going to monitor the parasitic current load while the Jeep has been parked for a few hours.

 

[alphawolff]

I just heard today from another co-worker that the NHSTA has de-certified stop/start systems due to possible safety concerns. Not sure as to the authenticity of that statement, but interesting if true.

 

[NWJeepr]

It was designed to cheat EU testing as well. EU goes even more crazy due to their fining system. It's why they have 20k mile oil change intervals. At least we're not at that level of insanity.

Can you provide a definitive source, or is that your personal (projected) opinion?'

I just heard today from another co-worker that the NHSTA has de-certified stop/start systems due to possible safety concerns. Not sure as to the authenticity of that statement, but interesting if true.

Is gathering information on the subject really that hard? Do you not have access to a search engine?

 

[Ratbert]

It doesn't always save fuel. For some people, it consumes more fuel. That's the point.

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.

 

[kah.mun.rah]

Call it 6%... For most of us that is less than 1 mpg. You can easily do better by simply changing your driving style.

Yep. Also, increasing your tire PSI by 1 probably gives the same fuel savings.

 

[Mikeb16]

That's a bit challenging to believe on face value. These things disable themselves whenever the stars aren't perfectly aligned, yet it kicked in when the battery was so bad that it couldn't start the Jeep again?

Situation was that she was stopped at a red light and the engine cut off like it normally does when the start stop actives and when the light turned green it never started back up. Luckily it happened near my work so I went to jump start it. I tried starting it without a jump box and all it did was click. She took it to the jeep dealer and the batteries both tested bad.

On my wrangler I normally disable the start stop when I get in the vehicle but I forgot one day and it shut off in traffic and had a hard start when I went to go again. Lights came on saying "auxiliary switches disabled low battery voltage" and come to find out both batteries were going bad.

 

[GabeBoyTheGreat]

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.

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.

 

[NWJeepr]

Yep. Also, increasing your tire PSI by 1 probably gives the same fuel savings.

Probably why modern vehicles tend to run higher tire pressures as well.

You know there is good data in the DoE and EPA studies which found the benefit can be a 25% increase in fuel economy from stop-start tech alone. Of course, those studies have been ripped down from those websites because, well...you know why. They don't support the current narrative. But those studies still exist, and the data was sound.

Also important to note, stop/start was never required in the US by the EPA or any other agency. Automakers were given credit for providing it under certain administrations, but it was not required.

So, it remains to be seen how the EPA is "fixing" this when it wasn't required...ever.

 

[alphawolff]

Situation was that she was stopped at a red light and the engine cut off like it normally does when the start stop actives and when the light turned green it never started back up. Luckily it happened near my work so I went to jump start it. I tried starting it without a jump box and all it did was click. She took it to the jeep dealer and the batteries both tested bad.

On my wrangler I normally disable the start stop when I get in the vehicle but I forgot one day and it shut off in traffic and had a hard start when I went to go again. Lights came on saying "auxiliary switches disabled low battery voltage" and come to find out both batteries were going bad.

I've seen the JL z-case fuse blow during stop start events at least ~100 times by now. I've seen the PCR relay fail on Pacificas a couple dozen times as well, preventing restarts. I've seen the WL grand cherokee fuse array blow, too. And that's just one tech at one dealer.

Seems to be really common across multiple OEMs. Hondas under investigation for ~2.2 million vehicles for the same issues. Shuts off at a red light then doesn't restart, which is a big safety issue.

Probably why modern vehicles tend to run higher tire pressures as well.

You know there is good data in the DoE and EPA studies which found the benefit can be a 25% increase in fuel economy from stop-start tech alone. Of course, those studies have been ripped down from those websites because, well...you know why. They don't support the current narrative. But those studies still exist, and the data was sound.

Also important to note, stop/start was never required in the US by the EPA or any other agency. Automakers were given credit for providing it under certain administrations, but it was not required.

So, it remains to be seen how the EPA is "fixing" this when it wasn't required...ever.

I don't think anyone is debating the authenticity of stop/start saving fuel. The issue comes from the systems themselves creating massive maintenance and reliability issues down the line making the original fuel savings goal a mute point.

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.

 

[Jeep Wick]

I've seen the JL z-case fuse blow during stop start events at least ~100 times by now. I've seen the PCR relay fail on Pacificas a couple dozen times as well, preventing restarts. I've seen the WL grand cherokee fuse array blow, too. And that's just one tech at one dealer.

Seems to be really common across multiple OEMs. Hondas under investigation for ~2.2 million vehicles for the same issues. Shuts off at a red light then doesn't restart, which is a big safety issue.



I don't think anyone is debating the authenticity of stop/start saving fuel. The issue comes from the systems themselves creating massive maintenance and reliability issues down the line making the original fuel savings goal a mute point.

Just to be clear, *all* emission and fuel saving devices are because of EPA targets. OEMs don't go out of their way to increase the price of their vehicle while decreasing reliability for shits and giggles.

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

 

[Dusty Dude]

It was simply showing how far off from reality our (Americans') estimates of ASS usefulness were. It showed the estimates, then showed reality.

I'm sure we've spent much longer trying to correct misunderstandings about what the video actually said to people that didn't watch it than it would have taken them to simply watch it, but that's our reality.

Isn’t that what forums are for? We are discussing items that were and were not in the video, but are relevant to the topic.

So I watched the video, and my question still stands. He started with a worthless survey, showed the vials based on the survey, jumped to an actual test, and didn’t show the vials.

That's a bit challenging to believe on face value. These things disable themselves whenever the stars aren't perfectly aligned, yet it kicked in when the battery was so bad that it couldn't start the Jeep again?

I agree, it is challenging, and was of the same belief, until it happened to my daughter in her Subaru last month. No prior indication of anything wrong with the battery.

 

[alphawolff]

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

I couldn't agree more. Even if the system gets you back going in under half a second, that's still time wasted in the event of an emergency.

My ass has been rear ended 3 times. I keep an eye on my rear view mirror like a hawk when I'm stopped at a red light these days.

So I watched the video, and my question still stands. He started with a worthless survey, showed the vials based on the survey, jumped to an actual test, and didn’t show the vials.

Eh, IIRC if the engine is off for at least 7 seconds turning it off will save fuel. Not really up for debate

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