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Mod Note : Please continue the discussion in our Turbos & Idling Article. Thanks
There is absolutely no such instruction in the C220 manual, or from the dealership, that the C220 should be idled for a short span before shutting off. Or moving.
Do modern turbos have superior lubrication or a solution for this?
Hmm.. i thought all this was over in new gen engines (crdi's askoda turbos).
It's usually recommended to idle the car or get a turbo timer which does the job for you.
I'm not sure about your case...the only turbochargings I've dealt with are petrol related. I'm sure MB knows what it's doing though.
Just a few basics.
I am assuming we all know how turbos work. Contraption bolted onto the exhaust manifold. Exhaust gases turn turbine which is connected to compresoor with a shaft, anf therefore puts in more air, allowing more fuel to be fed into engine, resulting in more power and big smile on face.
Now, since the turbo runs on exhaust gases it gets seriously hot, very seriously hot and it is virtually impossible to keep them lubricated with any self contained substance, because it would have a tendency to dry out and seize. Therefore in order to keep temperatures down, oil (for lubrication also) and water are used to keep turbo's cooler.
Now, when we really slam our vehicles, turbo's, like i mentioned earlier, tend to get fantastically hot, to the point that they even might burn up the oil that is being circulated thru it. As a result this burnt oil tends to crust up. This phenomenon is called COKING (pleae dont misunderstand for something that some late politicians son did, as a resul of which his insides needed to be washed out). This problem is accelerated further if after a spirited run the engine is shut off before it is suffciently cooled down. This crust is very abrasive and will spell the death knell for your turbo charger.
The basic construction of a turbo is directly related to the amount of friction within it's components which again results in the build up of heat. I am no expert but according to me, following might be some of the reasons why modern day turbo charged vehicles do not require idling before shut off: -
1) Older turbos used to use bushes, modern ones use ball bearings. These bearings are also fed with oil (design) and therefore are less starved of lubrication therefore resulting in less heat build up and therefore reduced chances of coking.
2) Most modern cars also use synthetic oild which vastly improve lubrication and cooling.
3) Some modern cars come equipped with Oil cyclers which continue to provide / pump oil into th turbo even after shut off.
4) Vast improvements to engine cooling components.
Insite of all of the above I personally would still idle my turbo vehicle before shut down. After all these are mechanical components and there is a chance of failure.
Appologies for the long post.
Thanks for the replies, Steeroid & Sideways. To be honest, I am baffled as to why this practice is not recommended in the manual or by the Benz tech guys.
Butttttttttttt since I have yet to find a conclusive answer of "why not to idle", I take the safe way out and let her idle for atleast 30 seconds. Even my driver has strict instructions on the same. The only thing is...its a bit inconvenient and I was hoping to find a convincing answer that modern day diesels have a bypass for this.
Till then....will let her idle.
Diesel turbos should not need any idling.
I have a petrol turbo and only time I idle it is when I am forced to park it after a hard drive. Other wise I dont and no issues so far 100,000+ miles and still pumping full boost.
Another small detail. Diesel exhaust gases (EGT) run cooler than petrol, and therefore, the turbo designs differ slightly.
Newer generation diesels offer adequate lubrication for the turbos. The 30 sec- idling rule is precautionary for preventing abrupt cut-offs. Usually, we park the vehicles before turning them off, and parking is done at very low (below 1500-2000) revs. Hence no danger, since the engine revs at low RPM's for the 30 secs or so it takes us to park.
My 2.0 TCIC Safari had a warning sticker on the RH bottom side of the dash, indicating a 30-sec idling for the turbo.
Turbo petrols, however, are a different ballgame. Turbo timers, BOV's, all mandatory. All of which non-existent in diesels.
One way of partly overcoming the problem is to time your stops properly. Mostly you will know when you are about to stop. As in park the car. Its better to stop reducing the speed a bit ahead. And if possible (say an empty stretch lies ahed before you stop) put the car in neutral. The RPM drops immediately (turbo kicks in only above a certain RPM) and yet the turbo is getting lubricated... that way it is akin to idling even on the move. And then you stop the car without much of a need for idling.
However if you were gunning down the road and then stopped suddenly you are better off idling the car for a while.
No need for idling. The only thing to watch out for is heat soke if the engine is shut off after high load. So just take the last two KM to the house easy.
Sideways is right. As far as I know, non intercooled turbos require an idle of about 30 seconds to prevent coking of the oils in the turbo. This problem has been eliminated in modern intercooled turbos, but nevertheless, it's still a good practice to maintain.
Mpower, your say your car is a petrol turbo. Do we apply the same practice to a diesel turbo?
IMO, Merc would know what they are saying.
Reg the Indian diesels, would be better to idle. My Sumo has the same 2.0 TCIC as the Safari, and idling is recommended. The 1.4 TC [no IC] Marina also needs an idling .
Quote:
Originally Posted by Sideways . This phenomenon is called COKING (pleae dont misunderstand for something that some late politicians son did, as a resul of which his insides needed to be washed out). ..............................
Insite of all of the above I personally would still idle my turbo vehicle before shut down. After all these are mechanical components and there is a chance of failure.
Appologies for the long post.
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You sound like you've had a goood sunday. I would agree with you on idling the turbo vehicle irrespectively. I have heard a lot of stories about blown BMW turbo's diesels in the UK. V few about Mercs unless they have been overengineered
@elf: Er...intercoolers are mounted at the intake stage of the engine, therefore it should have no bearing on the oil consumption and other working characteristics of the turbo.
Sir, I beg to disagree on the above. I do not know about the new DICOR engine, but the manual of my '98 Safari mentiones this and also a sticker is there on the dash that says that ideally the engine should be idled for a minute before and after starting & shutting the engine down. This I've followed didligently till date.
Also, acquired a Dec'04 Scorpio on 24th - Turbo 2.6 GLX. It too has a similar instruction as above. Maybe diesel turbos have such a requirement as above..
Quote:
Originally Posted by Steeroid
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