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-   -   Why you must practice the "Idling Rule" with Turbo-Charged Cars (https://www.team-bhp.com/forum/technical-stuff/131875-why-you-must-practice-idling-rule-turbo-charged-cars-19.html)

Yes. For all diesel engines and moreover for diesel cars that have a Turbocharger.

No problems at all. If the drive wasn't prolonged high RPM/highway cruising then the procedure you follow is good enough.

If it is sedate driving then 15-20 second idling is more than sufficient.

Im curious - why would a manufacturer provide a start-stop feature (Eg. Mahindra XUV Micro Hybrid) - which shuts off the engine within a few seconds of being idle at a red light etc?

Because, clearly, that engine/turbo doesn't require idling. Contrary to what some advise, I don't think there is a requirement or a common rule for idling, unless specified by the manufacturer and you will see more and more turbo engine that don't require idling. On top of that very few ordinary owners have ever heard of the idling rules as few people read the manual to start with.

Obviously, it cant hurt to leave the engine to idle. Whether its necessary you will find in the manual, not on the net.

The other thing, but that is more a personal observation, is that I yet have to see anybody in India redlining their engines. So, the real need for idling, if there is one, is remote. Few of us here in India find ourselves, regularly, in a situation where your engine has run for say 70-80% loading and then stop and having to switch off the engine.

Im not familiar with the exact stop/start logic built into some of these cars, but I can imagine that they might look at overall engine loading and duration and whether the engine needs to run at idle for a few seconds more or can be stopped straight away at the red traffic light so to speak.

Jeroen

I keep the start stop feature in my car deactivated at all times. I will switch it on for some time tomorrow just for some fun and see how it goes.

But as far as I remember, the engine shuts off 3-4 seconds after the car stops completely and after releasing the clutch in neutral. Will confirm tomorrow.

Could you try this:
In your typical city driving I find it hard to believe that the turbo gets anywhere near its top end maximum temperature. So, no matter what it can shut down the engine pretty quick as soon as stopped.
Can you try this as well
Really load up the engine for at least 5 -10 minutes, say some good motorway driving. Then pull over and leave the engine idle and see if it takes longer before it gets switched off.

Thanks
Jeroen

I drive a Skoda Octavia AT equipped with Start/Stop technology. Here are my observations:

I find when starting off in the morning that Start/Stop does not switch usually off the engine at the nearest signals (500m from home). However, it does switch off the car at the next signal, which is another ~2km away. I don't have the opportunity to go beyond 50kmph during this stretch. So the car hardly revs beyond 2000 rpm and the engine temperature is always well below the optimum temperature when I reach the signal.

The car switches off immediately when I stop after a highway drive (100-120kmph), for eg:, when I stop at a signal after taking an exit from the highway (so there is no chance to run at low engine speeds for any significant length of time). The behaviour is confusing since the manual also mentions that the engine should not be switched off immediately after driving at high speeds. These days I switch off the Start/Stop system when I go on a trip where I have to drive at 100kmph or more for a long time.

I guess the is a mechanism set in the program to let the turbo get the oil after the engine has switched off. Some kind of pump that runs for a while?

Else all Octavia AT and Scorpio owners would have busted turbo's - which isn't the case so there is some setup that's in place to cool the turbo after the engine stops.

I may be wrong though.

Another way of supplying engine oil to the turbo-bearing after the engine is abruptly switched off, is by having a small reservoir over the turbocharger itself. This oil will trickle down through the turbo-bearing due to gravity. No extra power is required.

This can work for a short duration as-in engine start/stop feature.

If you are going to rocket off at 100 after starting then yes, idle for 30 sec.
If you are going to drive the next 1 km at 20 km/h then no need to idle for 30 sec.

When shutting down always idle for 30 secs before switching off.

I recently hired a Mercedes A200. With the Start/Stop mode switched on, it would shut off the engine within split seconds as soon as I pressed the break and the car comes to a halt and again start as soon as I released a fraction of the pressure on the break pedal let alone pressing the accelerator pedal. On a typical Bangalore stop and go kinda crowded signal situation, the car would stop and start alteast 10 times till I crossed the signal. Also noted it wont idle a bit even if I had revved it hard and immediately stopped the engine at a signal/jam. I particularly experimented on this aspect quite extensively and I don't think there was any logic being applied by the ECU in sensing the Turbo spooling or the margin required for it to cool down. Am I missing something here?

OTOH, I take extreme care on all my own cars. I start keeping the car below 1500 RMP atleast 5 mins before reaching the destination and idle for 15~20 seconds before shutting the engine.

Truth is that modern turbo's are much resilient and often don't need any idling anymore. Check the owner manual to be sure Its a bit of a historical carry. Most people and I mean tens of millions, if not hundreds of millions have never ever heard of this rule, let alone think about it.

I would think that the very essence of a start/stop system depends on its ability to shut down quickly without cooling down. Apparently going by your experience it does.

Jeroen

A turbocharger needs to be cooled. AFAIK traditionally they've been cooled by oil.

So I guess when the car (& hence the turbo) is switched OFF immediately after prolonged usage, the heated turbo burns the oil abit, which I guess would lead to carbon deposits - which could reduce the life of a turbocharger by a significant margin.

If the Merc A200 has a water-cooled turbo (like the Linea T-Jet) , then the heated turbo could only burn the water into steam, which is harmless as there'll won't be carbon deposits.

Although modern oil-cooled turbo's are advanced, (and some {Edit : IIRC Zest has it.} even have an ECU control feature where the oil continues pumping for a minute after the car is switched off), I'd recommend a 30 second idling (as a preference, more than a rule).

Personally, in those 30 secs I switch OFF the A/c, headlights, disconnect my Belkin charger, take out the phone used for GPS navigation, take out stuff from the car etc.

:thumbs up

Water coooled turbo's (can) have oil too.

Here's what (used to) happens;The heat from the exhaust gases is transferred to Turbo casing and hence to the bearings. So when you shut down they are at high temperature. What (used to happen is the oil can become to hot, bascily start breaking down and you will have oil residues attaching itself onto the bearing surfaces. That in itself could present a problem for proper lubraction, if these residues get dislogded they end up in the oil lubricating system, might clog up stuff etc.

With modern turbo's a lot of what used to happen has been solved through better materials, better design and most importantly much better lub oils.

You cant hurt your engine by idling a bit. Whether it is necessary will be spelled out in the owners manual. More and more you will see it is really of no conern anymore.

As I stated before, only some car enthousiast are aware, all other drivers havent got a clue and dont seem to be experiencing to many turbo failures.

One additional reason could well be that most drivers dont really load up their engines at all. To put it differently, in most cases, before switching of you are very likely to drive slowly with low engine loading anyway.

But again, for safety, always check the owner manual. For piece of mind, do whatever you feel comfortable with.

Jeroen

Ok, I can talk about the BMW 2015 535i engine. This engine is called N54 or has another version N55.

It has a water cooled turbo, and once I turn off the car when the garage is silent, I can clearly hear water being circulated, and its very obvious. There is an electrical pump that does this circulation, depending on the turbo conditions.

The BMW manual does not talk about requiring idle rpms before shutting off.

However I have seen some car manuals talk about idling for a minute.

So as most say here, its the manual that counts for reference.

The literature for the T-Jet Engine indicates that it is both water cooled as well as oil cooled (there is a mention of both)
There is a direct line from the Coolant reservoir which can be seen in any pic of the engine bay.