Stop Start - How does it work?
Discussion
Morning all
I have just recently purchased a BMW X3 and the car has the stop start feature and an automatic gearbox.
Now when you come to a stop (in gear) the engine cuts out and you are left sitting in silence. Having grown up with various sheds this feels quite unnerving as I keep thinking the car has stalled
As soon as you put your foot on the accelerator the car starts and moves off in one go. It's like starting a car with the clutch pedal depressed and a gear engaged and as soon as the engine fires, releasing the clutch before you have even let the revs return to a normal idle.
My question about this is what is the engine and gearbox doing during this process?
Does stop start not cause unnecessary wear and tear on the engine and gearbox?
Thanks for your replies.
I have just recently purchased a BMW X3 and the car has the stop start feature and an automatic gearbox.
Now when you come to a stop (in gear) the engine cuts out and you are left sitting in silence. Having grown up with various sheds this feels quite unnerving as I keep thinking the car has stalled
As soon as you put your foot on the accelerator the car starts and moves off in one go. It's like starting a car with the clutch pedal depressed and a gear engaged and as soon as the engine fires, releasing the clutch before you have even let the revs return to a normal idle.
My question about this is what is the engine and gearbox doing during this process?
Does stop start not cause unnecessary wear and tear on the engine and gearbox?
Thanks for your replies.
V8KSN said:
My question about this is what is the engine and gearbox doing during this process?
Does stop start not cause unnecessary wear and tear on the engine and gearbox?
The torque converter wont be transmitting much torque until the revs rise significantly above idle, so I don't see why it should be a problem? Does stop start not cause unnecessary wear and tear on the engine and gearbox?
Not being very experienced with start-stop with automatics...
Does this mean every time you come to a stop with the transmission in drive the engine will quit? I know that on the manual cars i've seen this effect only comes into play when you are in neutral with the clutch up?
It does sound very intrusive.
Does this mean every time you come to a stop with the transmission in drive the engine will quit? I know that on the manual cars i've seen this effect only comes into play when you are in neutral with the clutch up?
It does sound very intrusive.
Daston said:
I have wondered what this is like on cars that are a bit older. I was crossing the road the other day and a 1 year old BMW had stop start (I guess it comes as standard). Was sat their with its lights on and sounded like it had to crank over a few times before it started to move.
Car must be poorly. Mines 4years old and 100,000 miles and it starts immediately. Saying that, standard protocol when I get in the car is to hit the start stop button followed by the DSC button.Petrol Only said:
kambites said:
The system doesn't stop the engine if it's not fully up to temperature.
Not true, well on my missus Golf anyway. It decides as and when it wants to work. EG Stone cold move 100 yeards. Stop/Start works
Drive 200 Miles without stopping. Stop/start does not work.
Weird.
I had a manual 1.6tdi bluemotion Golf as a company car. I read the handbook on the stop/start because it seemed to pick and choose when it worked.
Turns out there have to be a lot of prerequisites for it to function.
If you have the heaters on and the car isn't up to temperature it won't engage (No engine running = no heat for the blowers), it monitors the battery so if you're constantly stop/starting it won't engage (As to save the battery going flat), etc.
Turns out there have to be a lot of prerequisites for it to function.
If you have the heaters on and the car isn't up to temperature it won't engage (No engine running = no heat for the blowers), it monitors the battery so if you're constantly stop/starting it won't engage (As to save the battery going flat), etc.
anarki said:
I had a manual 1.6tdi bluemotion Golf as a company car. I read the handbook on the stop/start because it seemed to pick and choose when it worked.
Turns out there have to be a lot of prerequisites for it to function.
If you have the heaters on and the car isn't up to temperature it won't engage (No engine running = no heat for the blowers), it monitors the battery so if you're constantly stop/starting it won't engage (As to save the battery going flat), etc.
Yeah I had a read as well. Her car ignores all that. Turns out there have to be a lot of prerequisites for it to function.
If you have the heaters on and the car isn't up to temperature it won't engage (No engine running = no heat for the blowers), it monitors the battery so if you're constantly stop/starting it won't engage (As to save the battery going flat), etc.
Petrol Only said:
Not true, well on my missus Golf anyway. It decides as and when it wants to work.
Stone cold move 100 yards. Stop/Start works
Drive 200 Miles without stopping. Stop/start does not work.
Weird.
The logic within the system has to judge a number of items ok before it will activate the Stop/Start system, these include:Stone cold move 100 yards. Stop/Start works
Drive 200 Miles without stopping. Stop/start does not work.
Weird.
Outside temp
Engine temp
Battery charge
Load on systems (demister, A/C, lights etc)
If any of these are outside the set boundary the system won't activate.
Dangerous Dan said:
Not being very experienced with start-stop with automatics...
Does this mean every time you come to a stop with the transmission in drive the engine will quit? I know that on the manual cars i've seen this effect only comes into play when you are in neutral with the clutch up?
It does sound very intrusive.
I was a bit sceptical until I tried it. Even on an auto, you can avoid the system cutting the engine if you wish by just releasing the pressure on the brake until the engine fires, but before the car starts to creep (or kill it with the button obviously). After a while it becomes second nature. So much so, when I drive a car without S/S, I feel the need to manually turn it off with the key when stationary - sitting in a car going nowhere with the engine running feels wrong.Does this mean every time you come to a stop with the transmission in drive the engine will quit? I know that on the manual cars i've seen this effect only comes into play when you are in neutral with the clutch up?
It does sound very intrusive.
I borrowed a Jaguar XF that has s/s tech and found it annoyng. If you pulled up to a junction/lights/stationary traffic and stopped with your foot on the brake for more than a few seconds, it would stop (usually just as you were about to move forward again). However, if you came to a set of lights on red, put the handbrake on and released the footbrake, the engine stayed on unless you put it in neutral, so the actual time that it would be useful, it didn't work.
Okay, maybe having the car for more than 5 hours might get me to work out the tricks, but it just seemed too fussy. On the plus side, it didn't seem to delay setting off.
Okay, maybe having the car for more than 5 hours might get me to work out the tricks, but it just seemed too fussy. On the plus side, it didn't seem to delay setting off.
d 
.I know there have been a few threads on this, but I'll post what I posted on one of the SEAT forums.
These appear to be things that prevent stop start from working
With regards to fuel saving, it certainly saves me fuel. When stop start isn't working I sit there watching the average mpg tick down and down (because like you, I was interested in fuel savings vs wear). Manufacturers/magazines have a manner of different time lengths for how long you need to be standing for start stop to save you money. Some say 3, some say 5, some say 10, and some say 30 seconds. I've found 5-7 is probably a fair time.
These appear to be things that prevent stop start from working
- Car is not up to temperature
- Car has not moved far enough - I'm thinking about a traffic jam, when you only move a few feet or so. I believe it's because the car assumes you are parking/pulling a manoeuvre
- Reverse gear was the last selected gear - Again, car thinks your parking/pulling a manoeuvre
- Car is running a DPF regeneration - You may or may not get higher revs whilst idling too with this
- You have the windscreen blowers on - Not sure if this on all cars, but on my Leon, if I'm demisting the windscreen it doesn't allow stop start. With or without AC on (it defaults to AC on)
- You have the AC on with high fan speed - if I have AC/Auto climate on, it will stop the engine and turn the blowers down to the lowest speed. If I higher them up, it CAN restart the engine
- You are on a very steep incline - No idea why, especially as my car has hill start assist, but whatever
- You have engine/exhaust related faults - DPF pressure and EGT Temp sensors can cause this.
With regards to fuel saving, it certainly saves me fuel. When stop start isn't working I sit there watching the average mpg tick down and down (because like you, I was interested in fuel savings vs wear). Manufacturers/magazines have a manner of different time lengths for how long you need to be standing for start stop to save you money. Some say 3, some say 5, some say 10, and some say 30 seconds. I've found 5-7 is probably a fair time.
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