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Old 20th January 2021, 18:24   #1
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Default Turbocharged engines and the idling start / stop system

Many of us have been taught to let our turbo engines idle for a minute after a drive to allow the turbo to spool down gradually. I have been a faithful follower of this practice, and Team BHP recommends this too:

https://www.team-bhp.com/forum/techn...rged-cars.html (Why you must practice the "Idling Rule" with Turbo-Charged Cars)

However, the idle start-stop systems incorporated in today's cars seem to counter to this suggestion. The ISS systems are too aggressive and prepared to turn off the engines at the slightest instance. While this may not be so much of a bother in bumper-to-bumper traffic where usually the turbo never gets to spool, what about an example where you are cruising on a highway and then you reach a toll, you slot in to neutral and - the engine switches off?

What will be the impact on the engine? Are the effects of this immediate shutdown researched by the engine manufacturers? Theoretically, we do have a button to temporarily disable the start-stop system - but it is not ideal. The system resets to "on' every time the car ignition is turned off. There are instances where I would have turned off my ignition and after turning on again, I would have forgotten to disable the auto start/stop. Forget informed users, would the average user even know?

Considering so days many cars equipped with turbos also come with Idle Start/Stop (A few that quickly come to mind: Ciaz, Ertiga, S-Scross, DZire BS6, Mahindra XUV500, XUV300, TUV300, Hyundai Nios Turbo, and recently Altroz i-Turbo), should this be a cause for concern and should this call for an alternate solution?
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Old 20th January 2021, 18:54   #2
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Default re: Turbocharged engines and the idling start / stop system

Good point, I wonder why this didn't come up earlier, Thanks

No experience but guessing that in the usual start/stop traffic probably doesn't involve high boost and hence high turbo speeds so maybe not an issue but will let other BHPians clarify it.
I wonder what does the owner manual say about this.

Just asked a friend with a XUV300 and he had the same concern. He wants to keep the car idling while he is opening the gate and stuff but it shuts down.
He said its not easy to remember to switch it off after clearing traffic so its either off or on. He was more inclined to switch it off for good because even the service center had asked him to idle it before shutdown.

Last edited by shancz : 20th January 2021 at 19:07. Reason: added user exp note
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Old 20th January 2021, 19:18   #3
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Default re: Turbocharged engines and the idling start / stop system

Whatever start stop system I have come across turns the engine off after observing idle speed for a set few seconds, neutral gear and no load condition. If the engine Oil is OE and changed as per schedule, this is good enough.
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Old 20th January 2021, 19:25   #4
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Default re: Turbocharged engines and the idling start / stop system

Quote:
Originally Posted by railfanwithk750 View Post
What will be the impact on the engine? Are the effects of this immediate shutdown researched by the engine manufacturers? Theoretically, we do have a button to temporarily disable the start-stop system - but it is not ideal. The system resets to "on' every time the car ignition is turned off. There are instances where I would have turned off my ignition and after turning on again, I would have forgotten to disable the auto start/stop. Forget informed users, would the average user even know?
In most cases, these auto engine off systems are smart enough to know when it is safe to switch off the engine and when it is not. The algorithm used to decide when to switch off the engine does not work blindly every time you come to a stop. The system monitors several parameters including various temperatures, engine runtime since the start, and even the AC settings. The system algorithm considers all these parameters and switches off the engine when it is safe to do. At least this is how it is in most cars equipped with such a system (there might be exceptions to this, but then those would be the bad designs!).

So in summary, while this system is terribly annoying (I keep it disabled all the time in my car because I do not like the annoyance), there is no bigger danger in using this system if you are OK with it.

Last edited by Dr.AD : 20th January 2021 at 19:27.
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Old 20th January 2021, 19:25   #5
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Default re: Turbocharged engines and the idling start / stop system

The whole idea of letting you engine/turbo idle a bit before shutting it down is becoming less and less relevant on modern cars/engine.

If you want to know what is good for your engine/turbo; first and foremost consult your owner's manual. If it is not mentioned, it is simply not required. Feel free to idle, but other than polluting the air a bit longer it is not going to make any difference.

Here is another thought: There are literally hundreds of millions car owners around the globe who have never heard of idling their turbo engine before shutting it down. Hell, my wife would not even know if she was driving a turbo charged engine anyway, and she is probably in very good company. It is only a worry on car forums, but virtually not in the average car owner world. Its not as if the roads are littered with blown up turbo’s.

Cars with engine start and stop system are designed specifically to handle the uh, start/stop requirements. And certain components are upgraded, e.g. battery springs to mind. But maybe also starter.

Some of our cars have start/stop systems. Not quite sure how their start/stop logic works, but certainly the condition under which it stops the engine is a bit more elaborate then being in neutral and or brake for a few seconds. So if there is a need to idle a bit, that can easily be accommodated in the start/stop logic if and when required. Similar what Dr. AD mentioned in the previous post.

It is also good to understand under which circumstance your engine and thus your turbo is really loaded. Just cruising on the motorway at 100 km/h is not loading up your engine at all. Unless you are driving something heavily underpowered. On most cars cruising will take 20-30% of the maximum available horsepower/torque.

The minute you come off the throttle, no fuel is injected and only air is blown through the engine and turbo. So when you come to a full stop at a toll from a normal cruising speed, the engine nor the turbo were particularly loaded and before you come to a normal stop, lots of air and no combustion has been taken place for 15-30 seconds already depending on how you anticipate and slow down for the toll.

In fact, coming off the throttle is a far more effective way of reducing temperatures in your engine/turbo than idling, because the volume of air is so much higher (proportional to the RPMs of course).

So unless you were barreling down the motorway, pedal to the metal for quite some time, slammed on the brakes in an emergency stop, not a single part of your engine/turbo reaches anywhere near maximum temperatures.

Again, always check what the manufacturer owner manual says. I would say the chances are they know a lot more than the internet at large!

Jeroen

Last edited by BlackPearl : 20th January 2021 at 21:45. Reason: Minor typo. Thanks.
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Old 20th January 2021, 19:34   #6
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Default re: Turbocharged engines and the idling start / stop system

Quote:
Originally Posted by Kosfactor View Post
Whatever start stop system I have come across turns the engine off after observing idle speed for a set few seconds, neutral gear and no load condition. If the engine Oil is OE and changed as per schedule, this is good enough.
Not sure of other models, but at least on S-Cross, I've had a couple on instances where the engine goes into shutdown mode the moment I get to zero and engage neutral, even if I have been cruising at 90 for an hour. Owners of Ciaz / S-Cross / Ertiga would be able to testify the same.

Edit: I replied just a moment before Jeroen sir's post so missed the post. The logic makes sense, I am on the conservative end of the spectrum, always maintaining 85-90 on highways and tend to let off the throttle and let engine braking do it's stuff. Does that give enough time for the turbo to spool down on it's own?

Last edited by railfanwithk750 : 20th January 2021 at 19:58.
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Old 20th January 2021, 20:19   #7
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Default re: Turbocharged engines and the idling start / stop system

Jeroen's post is apt.
Did a quick check of the XUV300's manual.
Some extracts from the online manual :

Even for cold starts it discourages idling, the engine start system handles that by raising the rpm and them rolling back to normal after operating temperature is reached.

Name:  XUV300_ColdStart.png
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Recommends a few seconds of idling before shutdown.

Name:  XUV300_stopping.png
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The ESS considers a variety of parameters before stopping the engine so like mentioned it should be smart enough.

Name:  XUV300_ESS.png
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Size:  226.5 KB


So the auto-start-stop system can be used without any concerns in modern turbo engines, the manufacturers wouldn't have put it in if there was any.
But good to know, at least cleared my doubts and will also share this with my friend.
Thanks

Last edited by shancz : 20th January 2021 at 20:37. Reason: concl line
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Old 20th January 2021, 20:38   #8
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Default re: Turbocharged engines and the idling start / stop system

I am not so concerned about the ESS system being activated in city traffic, since the gap between the stop and start will be small, and most times the engine has already warmed up. But where I would look for this is at the end of the drive, when we are parking for a long time. The conventional info is that the oil needs to settle down by the turbo running at low speed, and we then switch off the engine. But I dont see how the ESS can make out that this is end of the trip. Do we need to /have a switch to enable/disable ESS ? and if yes, do we use this each time at start & end of trip ?

Last edited by condor : 20th January 2021 at 20:46.
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Old 20th January 2021, 21:09   #9
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Default re: Turbocharged engines and the idling start / stop system

What a statement this, which sums it up:
Quote:
Originally Posted by Jeroen View Post
Here is another thought: There are literally hundreds of millions car owners around the globe who have never heard of idling their turbo engine before shutting it down. Hell, my wife would not even know if she was driving a turbo charged engine anyway, and she is probably in very good company. It is only a worry on car forums, but virtually not in the average car owner world. Its not as if the roads are littered with blown up turbo’s.
Good and relevant topic and a great post by D-BHPian Jeroen.

Quote:
Originally Posted by Jeroen View Post
So when you come to a full stop at a toll from a normal cruising speed, the engine nor the turbo were particularly loaded and before you come to a normal stop, lots of air and no combustion has been taken place for 15-30 seconds already depending on how you anticipate and slow down for the toll.
The point mentioned in the post above is inline with what is described in one of the user manual. (This is of Scorpio's).

Turbocharged engines and the idling start / stop system-20210120_204945.jpg

I think this condition will be met in city traffic as well as stopping after a cruise on a highway, unless an abrupt stop is made after a hard drive, as mentioned in the post too. With that, the start/stop (micro hybrid, in Mahindra's books) function should not be causing any harm.

Last edited by balenoed_ : 20th January 2021 at 21:10.
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Old 20th January 2021, 21:32   #10
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Default re: Turbocharged engines and the idling start / stop system

I don’t think the ESS system in SCross is really intelligent. I’ve found that even in extreme mumbai heat, with the ACC set to 20, it stops the moment I hit neutral + standstill. It restarts after about 1.5-2 minutes (not timed, memory estimate) of inaction. When the delta between outside temperature and ACC is lesser, it stays shut for about 30seconds longer. Also if the car rolls in neutral, the engine comes to life only if the rolling is sustained for approx 2-3meters.

But it definitely doesn’t idle after a trip end or sustained driving. Does it mean that after a highway run I should turn the ESS off to let the idling happen, before killing the engine?
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Old 20th January 2021, 22:01   #11
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Default re: Turbocharged engines and the idling start / stop system

Quote:
Originally Posted by condor View Post
But I dont see how the ESS can make out that this is end of the trip.
Do we need to /have a switch to enable/disable ESS ?
and if yes, do we use this each time at start & end of trip ?
Guessing here but the ESS would check the engine/coolant temperature, maybe this can prevent a engine-stop if the temperature high ?
Talking of the XUV300, the switch is already there and it remembers the setting(manual switch), if that's what you are asking. But remembering to switch it on/off based on the trip won't be feasible so will just trust the manufacturer on this


GreyNomad just saw your post, I would suggest to check the manual for your case, especially the engine-start. What I figured in the XUV300's manual is that they mention a idle of "a few seconds" and the ESS waits for "a few seconds" before switching off if all the conditions are satisfied, so that seems covered. Also, the turbo is dependent on the engine RPM, A/C won't really make a difference to the turbo.
Switching off the system ? I don't think so. I would just trust the manufacturer on this and also like Jeroen said even after a long drive the engine might not have been "loaded" or the slowing down phase before parking would be quite effective in cooling off the turbo.

Last edited by shancz : 20th January 2021 at 22:15. Reason: missed post response
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Old 20th January 2021, 22:16   #12
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Default re: Turbocharged engines and the idling start / stop system

Quote:
Originally Posted by shancz View Post
Guessing here but the ESS would check the engine/coolant temperature, maybe this can prevent a engine-stop if the temperature high ?
Once the engine temp reaches optimal temp, it stays there. Temperature will not increase continuously.

example: if I have a 10km trip, the temp reaches normal working temp in about 3-4km, and will remain there till the end of the 10km drive. So how will the system know that the engine is at km 5 or km 10 ?
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Old 20th January 2021, 22:18   #13
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Default re: Turbocharged engines and the idling start / stop system

@shancz will check the manual.
WRT the ACC/ESS correlation, IIRC one of the parameters for the engine to restart is the cabin temperature.
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Old 20th January 2021, 22:24   #14
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Default re: Turbocharged engines and the idling start / stop system

Quote:
Originally Posted by condor View Post
example: if I have a 10km trip, the temp reaches normal working temp in about 3-4km, and will remain there till the end of the 10km drive. So how will the system know that the engine is at km 5 or km 10 ?
True, it cannot. But what I wonder is will the turbo be hot enough to cause any issues in that case ?
And I am just thinking out loud here, absolutely no experience or competency about a turbo.

Taking a leaf from the XUV300 manual, all mentions are "a few seconds" for idling before shutdown either by the ESS or manually. I am not sure how many seconds that is. So that's why going by the logic that if they put it there they must have thought about it

GreyNomad, Sorry saw your post late again, will quote the next time for sure
XUV300 didn't mention anything about the ambient temperature, but I haven't gone through the entire section.
About the rolling in neutral, there should be a speed check as well.
Here are XUV300's :

Name:  xuv300_ess_astart.png
Views: 6231
Size:  20.8 KB

Last edited by shancz : 20th January 2021 at 22:37. Reason: typo
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Old 20th January 2021, 22:47   #15
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Default re: Turbocharged engines and the idling start / stop system

Quote:
Originally Posted by GreyNomad View Post
I donít think the ESS system in SCross is really intelligent. Iíve found that even in extreme mumbai heat, with the ACC set to 20, it stops the moment I hit neutral + standstill. It restarts after about 1.5-2 minutes (not timed, memory estimate) of inaction. When the delta between outside temperature and ACC is lesser, it stays shut for about 30seconds longer. Also if the car rolls in neutral, the engine comes to life only if the rolling is sustained for approx 2-3meters.

But it definitely doesnít idle after a trip end or sustained driving. Does it mean that after a highway run I should turn the ESS off to let the idling happen, before killing the engine?
W.r.t. the ACC, you can actually set the parameter from the MID menu under "IS A/C" option. There are three levels, Economy, Default and Comfortable. With the economy option selected, engine will switch on least often when the Auto Stop is active. With the "Comfortable" option, engine will switch on more frequently to keep the cabin cool.
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