[vwcrusher]

New member here; was speaking to a friend who suggested that I should not engage the engine shut down feature on my 2017 M240i xdrive as the turbo will still be spinning quite fast with the oil supply shut off. This will wear the bearings prematurely. I called my local dealer asking if this might be true, and the response was that it actually might be true.

Does anyone have any experience with this. My concern is that while saving a few dollars on gas it might be at the expense of a turbo bearing ($$$).

Thanks.

[amw896]

true, to an extent. The feature only shuts down the system for short periods and under normal driving your turbo won't be on boil so it's not a huge deal. If you're driving it hard, then I would recommend turning the feature off. This is also why the feature defaults to the off position in sport+.

[morphomeman]

If I remember correctly, it doesn't shut off in Sports either, though it is very early in the morning and I could be wrong.

[aozer]

it can cause premature wear on engine components. it is even mentioned in the users manual.

the savings are pretty negligible, it really isnt even worth using. those few dollars you save in gas may come back to bite you in the ass if you plan to keep the car for a long time.

[overcoil]

Originally Posted by aozer

it can cause premature wear on engine components. it is even mentioned in the users manual.

the savings are pretty negligible, it really isnt even worth using. those few dollars you save in gas may come back to bite you in the ass if you plan to keep the car for a long time.

Agree about the fuel savings.
Was under the impression the start/stop feature was to reduce emissions from idling cars particularly in congested areas. As much as I hate start/stop, it really is kind of amazing how smoothly the car restarts when the driver is ready to continue.
Also, I'm starting to see signs in more places that tell you not to let your car idle in this area: parking garages, near door openings, schools.

[p912guy]

Agree, auto start/stop is much more about the environment (reduced emissions) than fuel savings. We have it disabled on both my BMW and my wife's Audi. That's not to say we are anti-environment, but I'd rather avoid increased wear and tear on my car and maybe save the environment by keeping worn parts our of landfills and reduce use of hazardous chemicals with increase vehicle service.

[TajoMan]

It is possible to have some turbine spinning after engine shutoff but it wouldn't be too bad.
Stresses on those bearing without real load won't be a lot.

I would worry more about starter, piston rings, cylinder wall. Those could wear out prematurely at every engine start.

I never uses idle off feature anyway. It's just a feature to satisfy emission regulation.

[Maynard]

Not that I'm a fan of the auto-off feature, but I believe that modern turbo designs have largely solved the problem that this post refers to. The original turbos had only oil to cool them, and they run at very near exhaust-gas temps during actual driving. So if you just pull up from driving and shut the car off immediately it would overheat and coke the oil (turns it into s/t resembling the most expensive rock-candy). This gave early turbos a real bad reputation for reliability, and spawned lots of suggestions to let the car idle for a while before shutdown so you'd circulate more oil to cool it (and some add-on gizmos to delay shutdown). Now they are built better, and with more cooling. I suspect that there is even oil circulation after shutdown just for this purpose. I'd worry more about wear to the starter system than anything else, but with parts prices like these, it wouldn't make financial sense if it put wear on the turn signals.

[vwcrusher]

Post Update: I decided to speak with an indy BMW mechanic about this, and his advice was essentially the same as my friend's. He noted that it's the bearings in the turbo that would suffer without sufficient lubrication.

So bottom line, at least for me at this point (until more data is available) is to leave the auto shut off feature disabled. It also seems to me that many cars now come equipped with turbos; I wonder if there has been any guidance issued......

[TajoMan]

Originally Posted by vwcrusher

Post Update: I decided to speak with an indy BMW mechanic about this, and his advice was essentially the same as my friend's. He noted that it's the bearings in the turbo that would suffer without sufficient lubrication.

So bottom line, at least for me at this point (until more data is available) is to leave the auto shut off feature disabled. It also seems to me that many cars now come equipped with turbos; I wonder if there has been any guidance issued......

I'm 100% sure that BMW (or any other manufacturer) tested and validated the long term durability of all affected components by idle shut off feature.
(although 'long term' can mean very subjective. whatever BMW targets at)

If it is very new technology, I would worry about it but idle shut off has been around more than 5 years now.
Technology is pretty mature. (whether it's effective to save fuel/emission in real life or not)

I've seen lots of mechanics or technicians who are very smart and knows lots about cars and tech, but they have limited access to actual controlled test data and/or warranty data, which manufacturers have. They can speculate but they cannot actually confirm it, based on reliable test data.

In theory, I do agree with that mechanic. It is possible that lack of oil flow may damage the turbo bearing in long term.
In reality, it is very unlikely it will lead to turbo bearing failure.

Like I mentioned, starter will be #1 concern followed by piston/cylinder wall.

If you worry about turbo, then make sure your water pump works properly.

Regarding the idle shut off feature, I don't think anyone likes it (regardless of reliability issue).
I keep that stupid feature turned off all the time.

[SteveInfante]

Modern BMW twin scroll turbos (twin power) are capable of mitigating heat and friction stress better than a traditional turbo was able to. The start/stop feature isn't worth the extra stress on all the components involved in starting the motor multiple times in one trip for the sake of saving a few pennies worth of fuel. That's just my opinion of course.

[SPinder]

Entertaining and informative.

[kivyee]

The turbo is idling down at the point and I wouldn't worry about lack of lubrication. Whatever oil remains is more than enough for the turbo slowly wind down. My more immediate concern would be heat if e.g. you pull up to a stop light after a hard run. The stoppage of oil and water circulation while the manifold was still red hot will cause whatever oil remaining in the turbo bearing and housing to burn and coke. From my understanding though, on BMWs I believe the water pump keeps running for a period of time after shutoff, so that should keep the turbo cool.
I agree with what was mentioned. Personally I think start-stop is a big strain on the starter with negligible emission savings.

[ianp622]

1. It's not like the oil suddenly disappears.
2. Heat isn't a concern because the turbo has an electric coolant pump.
3. People that claim auto-start-stop is going to noticeably ruin your engine's lifespan are basing this off of old batteries, old starters, and other wear components, all of which have been updated to handle the extra start cycles. Look at the Prius, which has start-stop and is one of the most reliable cars out there.
4. "Expert" John Cadogan says a lot of dubious stuff - can't remember exactly which video but he was saying some BS. And "cold starts" are not applicable - it won't turn off if it's cold.

[Dylan86]

Originally Posted by TajoMan

It is possible to have some turbine spinning after engine shutoff but it wouldn't be too bad.
Stresses on those bearing without real load won't be a lot.

I would worry more about starter, piston rings, cylinder wall. Those could wear out prematurely at every engine start.

I never uses idle off feature anyway. It's just a feature to satisfy emission regulation.

This, imo.

When I had my drag cars I'd often start them up with the DP off to make sure all was okay before re-assembling the rest of the turbo setup. The turbine will spin for a few seconds, but nowhere near a level of RPM or duration time that would cause premature failure of the turbo/bearing due to lack of oil. There is always oil in the CHRA, even without oil pressure from a running engine (it's just not pressurized). I personally wouldn't stop using the start/stop feature simply to prolong turbo lifespan, that's a bit of an "extreme" measure, imo..

I personally do not use the feature for my own reasons, which are fairly aligned with TajoMan. The wear on the clutch (MT), starter motor and rotating assembly would be my first concerns, and potential for other areas of added wear that are unknown, equate to this just not being something I'm interested in utilizing.

Imagine a regular non start/stop driver, starts their car on an average of 4x daily, commuting to work, grocery store's/gas etc. (I know this could be higher, or lower, but for comparison I feel it's fair as there are some days running errands you can start your vehicle 10+ times, and other days only to and from work so only 2 starts). Then you have a start/stop user who will retain that same average, but now factor in every stop light/traffic jam/drive-thru/drop kids off scenario's and we're talking about 10x the use of the starter motor (or more) along with the added wear of the engine start/stop process.

I don't see the value in fuel savings, I only see the added wear/tear. If it were a lease and an automatic I might let the car do it's thing, because not being concerned about long term wear, who gives a F, right?

Just my $.02