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

[Ratbert]

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

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[Vinman]

Thats great if you drive primarily in stop and go city traffic.
Now, what about the rest of us that do primarily highway driving and seldom come to a stop (as compared to city driving). We are hauling around an extra bit of weight and obviously a more complex system with next to no benefit.
And while my driving style tends to get me the best fuel economy possible the day I become that concerned about fuel mileage is the day I start walking everywhere.

 

[2nd 392]

Thats great if you drive primarily in stop and go city traffic.
Now, what about the rest of us that do primarily highway driving and seldom come to a stop (as compared to city driving). We are hauling around an extra bit of weight and obviously a more complex system with next to no benefit.
And while my driving style tends to get me the best fuel economy possible the day I become that concerned about fuel mileage is the day I start walking everywhere.

Well yeah, but think about the hit the aftermarket would take it it didn’t exist. Look at all the devises to disable it just for Jeep, there are others like Range Technology for GM, I certainly don’t know all of them that are sold. You want the economy to tank ? look at the big picture. at least Wranglers have an off button … for now anyway, it’s just a PITA, added complexity, and weight, some vehicles have eliminated your choice to turn it off. A deal breaker for me.
Also for vehicle reviewers who have said it would be a deal breaker for them in the review.
Next discussion MDS. I have seen no noticeable mpg improvement since disabling it. Full disclosure, I minimized and avoided it before the NoLimitz. I didn’t buy a Wrangler for an economy vehicle, certainly not a V8 one.

 

[NWJeepr]

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

 

[flick2614]

Never trust a man that drives a Subaru.

For the longevity factor of the motor I’ll waste fuel idling.

 

[Terrymo]

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

In his right hand how much fuel a small 4 cylinder engine uses idling for 3.6 minutes. In his left hand, how much fuel is used to start that same engine. Just cause I’m a helper.

 

[Sidewalk]

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

Jason is a mechanical engineer, famous for using a white board for showing all his automotive math, and is a very big car nut.

 

[AmericanPatriot100]

Engineering Everything is awesome. I’ve learned a lot of automotive knowledge from his videos. I’m not sure why back in the day it was more cost effective/fuel efficient to leave the car idling at a stop light or drive thru instead of shutting it off and restarting it. But I used to do that and my dad always told me my car was using more fuel to restart it then it was to leave it idle for 30ish seconds. Now it’s the other way around. And if I leave my ASS on it still restarts itself if I’ve sat too long at a light even if I haven’t put my foot on the clutch again. I try to always turn it off because I one stop light on my commute in town and I always get stuck there and it’s like 2 minutes long and the car just restarts anyway.

 

[Aonarch]

I haven't watched that video in a while, but I believe it can save up to 4% in the city.

For me, it's not worth the wear and tear.

 

[AmericanPatriot100]

I haven't watched that video in a while, but I believe it can save up to 4% in the city.

For me, it's not worth the wear and tear.

I just watched it and 4%-8% is what it saved on the 4 tests in city driving. Not worth it for me either. Even though he said engineers took into consideration the more frequent starts and wear they also have a completely different/separate starter for the ASS system then the regular starter.

 

[flyer92]

I don't know the answer to OP's question, but I can tell you that the more ASS you haul, the more fuel you'll consume.

 

[Dusty Dude]

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.

 

[AFD]

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.

Maybe a bit long, but the few traffic lights I always get stuck at when driving on the outskirts of a very small city seems pretty damn close, but those are allowing for more than just 2 directions of traffic (usually 3 or 4 different roads converging, and I'll often get stuck not getting through on the first loop). I'll usually re-enable my ESS for those, but further into the city, they're a lot shorter and not worth the brief shutdown.

 

[AmericanPatriot100]

One of the kids in my son’s school did a science experiment a couple years ago on stop light duration. In the city the average wait is 30s or less in rural towns it’s 1.5min or less.

 

[alphawolff]

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.

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