Start-Stop - Does it save fuel?

[RamFan]

As Start-Stop becomes more readily available in the U.S. market, it's only logical that we'll see more and more people asking about it's efficiency and whether or not it's a solution in search of a problem. I've driven vehicles with this feature before but the Alfa is the first I've owned with the feature. Since purchasing, I've driven with the feature disabled, not because I didn't believe it worked, but because I didn't like the transition from brake pedal to accelerator. Over the past week or two I've forced myself to leave the feature engaged and try to get used to it. It's been successful so far, learning the "trigger point" so to speak has allowed me to basically decide when I want to engage the feature at a stop and when to bypass it. While this evidence is anecdotal, I've seen an instant jump in fuel efficiency of approximately 1.5mpg in my daily commute. I decided to dig into this a little and see if there was some true evidence showing a point of diminishable return with the vehicle being turned off and restarting versus letting it idle. Basically, I was looking to see how much idle time equals the amount fuel consumed in restarting the vehicle. In the old days with carbureted engines, starting a vehicle could consume a considerable amount of fuel as opposed to idling it. With todays computer inputs, the amount of fuel startup fuel is drastically decreased. While it's old (2007) this analysis is one of the most comprehensive documents I've found on the subject. While no two vehicles and driving patterns are the same, this does present some pretty good information. Enjoy the read! If you have some of your own on the topic, please be sure to share Tldr; A few seconds of idling consumes more fuel than the starting procedure of a vehicle.

 

[Virtus_Probi]

I wonder if a very mild regenerative braking system could easily store enough energy to quickly start a warm engine with no fuel penalty...??? Maybe the gains would be so tiny as to make it not worth considering....

 

[Quattro Pete]

 

[CharBaby]

I think the jury is still out in regards to the Start-Stop system saving fuel. I suppose it can but, I hear both sides. You'll have to measure it for yourself with/without during some serious city stop & go or slow & go traffic. I think this is where you'll see the largest benefits rather than the normal running around(combine driving). And of course, you won't see any benefit on the hiwy.

 

[paulri]

Quattro Pete beat me to it--the Engineering Explained video. His number was also 7 seconds (the amount of time idling, that burns up the same amount of gas as starting the engine), although both appear to be engines for small cars. I don't know if a larger engine will burn more fuel while idling, or require more fuel when starting, or both.

 

[demarpaint]

It is supposed to save fuel, I'd guess in some instances it does, and some it might not. The question is does it save enough fuel to save the owner of the vehicle money? Figure what it costs to have the system in the vehicle, maintain it, and the amount of fuel it saves the owner. Will the fuel savings exceed the cost of of the system and maintenance? If so then it might be worth it to some. I have a feeling saving the owner money doesn't matter, it's all about CAFE.

 

[ragtoplvr]

for me the figure of merit is total operating cost over 300K miles. there are 3 common systems. 1. Enhanced conventional starter. 2. motor alternator belt driven. 3. motor in transmission. 1. What I am hearing is town driven cars with this starter need a starter replaced as soon as 100K miles and they cost more. lets assume a starter at 100K VS a starter at 200K for the normal car. Assume 30 MPG compard to 31MPG qith the system. In 100 K at 30 mpg 1 mpg improvement saves $220 at about $2.00 gallon. so the extra cost of the starter is likely to eat up the savings. 2. I do not know the durability of the belt driven systems, I have heard of anecdotal evidence that the belt and tensioner fail sooner. ..I would expect the starter alternator to last a normal life, there is a electronic driver, I have no ideal what it costs but I expect if it failes you are out 500 to 1000 dollars. 3. Not apply, usually a full hybrid. I conclude that any possible savings will be consumed in additional maintenance and possible shorter engine life. Save fuel yes. Save money, probably not. Rod

 

[Kestas]

Originally Posted by ragtoplvr

... so the extra cost of the starter is likely to eat up the savings....

Unfortunately, this seems to be the case for much of our automotive technology. Cars are turning into large Rube Goldberg machines.

 

[KrisZ]

Originally Posted by ragtoplvr

for me the figure of merit is total operating cost over 300K miles. there are 3 common systems. 1. Enhanced conventional starter. 2. motor alternator belt driven. 3. motor in transmission. 1. What I am hearing is town driven cars with this starter need a starter replaced as soon as 100K miles and they cost more. lets assume a starter at 100K VS a starter at 200K for the normal car. Assume 30 MPG compard to 31MPG qith the system. In 100 K at 30 mpg 1 mpg improvement saves $220 at about $2.00 gallon. so the extra cost of the starter is likely to eat up the savings. 2. I do not know the durability of the belt driven systems, I have heard of anecdotal evidence that the belt and tensioner fail sooner. ..I would expect the starter alternator to last a normal life, there is a electronic driver, I have no ideal what it costs but I expect if it failes you are out 500 to 1000 dollars. 3. Not apply, usually a full hybrid. I conclude that any possible savings will be consumed in additional maintenance and possible shorter engine life. Save fuel yes. Save money, probably not. Rod

Or get a model where one can easily and permanently disable the stop/start feature and enjoy having a beefed up starter that will pretty much be guaranteed to last the lifetime of the vehicle and a bigger battery that should last longer as well.

 

[badtlc]

Originally Posted by Virtus_Probi

I wonder if a very mild regenerative braking system could easily store enough energy to quickly start a warm engine with no fuel penalty...??? Maybe the gains would be so tiny as to make it not worth considering....

I thought mazda did this with some capacitors.

 

[knerml]

Start/stop saves very little fuel, because in normal driving there is minimal idle time. HOWEVER, during EPA fuel mileage testing, there is a significant amount of idling time. So, start/stop feature producing an artificially high MPG rating.

 

[demarpaint]

Originally Posted by ragtoplvr

for me the figure of merit is total operating cost over 300K miles. there are 3 common systems. 1. Enhanced conventional starter. 2. motor alternator belt driven. 3. motor in transmission. 1. What I am hearing is town driven cars with this starter need a starter replaced as soon as 100K miles and they cost more. lets assume a starter at 100K VS a starter at 200K for the normal car. Assume 30 MPG compard to 31MPG qith the system. In 100 K at 30 mpg 1 mpg improvement saves $220 at about $2.00 gallon. so the extra cost of the starter is likely to eat up the savings. 2. I do not know the durability of the belt driven systems, I have heard of anecdotal evidence that the belt and tensioner fail sooner. ..I would expect the starter alternator to last a normal life, there is a electronic driver, I have no ideal what it costs but I expect if it failes you are out 500 to 1000 dollars. 3. Not apply, usually a full hybrid. I conclude that any possible savings will be consumed in additional maintenance and possible shorter engine life. Save fuel yes. Save money, probably not. Rod

That's my point. Too bad it is jammed down our throats. If they sold l it as an option I'd pass, I would bank the savings and let the engine run until I shut it off. Going forward turning the system off by pushing a button is probably not going to be an option. So disabling start/stop will require a hack or paying for a device to disable it, adding even more cost to a vehicle for people like me who want no part of it.

 

[jeepman3071]

In the real world, it saves very little fuel. Unless you are someone who constantly idles your vehicle for minutes at a time I don't really see any benefit. It's basically an expensive way for manufacturers to get 1 mpg for CAFE.

 

[RamFan]

Originally Posted by Char Baby

I think the jury is still out in regards to the Start-Stop system saving fuel.

According to which jury?

Originally Posted by demarpaint

it's all about CAFE.

These systems have been in place in Europe for years. The earliest of which were introduced in the 80s. While adoption in the US might have CAFE as a catalyst, these systems have existed long before US adoption.

Originally Posted by ragtoplvr

1. What I am hearing is town driven cars with this starter need a starter replaced as soon as 100K miles

Where are you hearing this from? As mentioned above, these systems have been in place in Europe for years and they haven't seen a string of premature failures.

 

[BMWTurboDzl]

Originally Posted by knerml

Start/stop saves very little fuel, because in normal driving there is minimal idle time. HOWEVER, during EPA fuel mileage testing, there is a significant amount of idling time. So, start/stop feature producing an artificially high MPG rating.

Depending on engine size it's about 5 percent which is a lot.

 

[Wolf359]

Mercedes had it on the 2014+ E-350 models. From the forums, it appears that the starters are fine, but what typically fails is the aux battery that's used for the start stop system. And they're typically failing in under 4 years so factor in the cost of the aux battery. At least it's not as expensive as the main battery. Also I think it's pretty standard that most manufacturers don't let you disable the system permanently, I think only a couple allow you to do it. I had a original starter last over 200k+ in a previous car and they don't seem to fail as often as the past. Alternators still seem to fail on a pretty regular basis though.

 

[NO2]

I have to agree that start/stop helps a lot. We rented a Passat Diesel Eco model in the UK and averaged 58 mpg (US gallons) combined in 80% city, 20% highway 2000 mi trip. The car completely shut off when stopped.

 

[Pelican]

Originally Posted by demarpaint

It is supposed to save fuel, I'd guess in some instances it does, and some it might not. The question is does it save enough fuel to save the owner of the vehicle money? it's all about CAFE.

It has never been a question of savings for the owner, but everything to do with CAFE

 

[BMWTurboDzl]

Originally Posted by Pelican

Originally Posted by demarpaint

It is supposed to save fuel, I'd guess in some instances it does, and some it might not. The question is does it save enough fuel to save the owner of the vehicle money? it's all about CAFE.

It has never been a question of savings for the owner, but everything to do with CAFE

Come on now, over the past 50 years just about every advancement in automotive technology related to the drivetrain has occurred for efficiency and emissions.

 

[bunnspecial]

Originally Posted by Virtus_Probi

I wonder if a very mild regenerative braking system could easily store enough energy to quickly start a warm engine with no fuel penalty...??? Maybe the gains would be so tiny as to make it not worth considering....

My mom's Buick(2014 LaCrosse) does this, along with using the same motor for assist under heavy acceleration. Back in December, the unit failed rather catastrophically, although fortunately under warranty. I think the repair bill(of course, she didn't pay anything) was ~$3K. I didn't hear it, but all the spectators thought the engine sounded like it was about to throw a rod.