[dadu]

Originally Posted by thoma

I have my doubts about this though. I thought the inter-cooler comes into picture only after the air has been compressed through the turbo's turbine, and that it does not aid in cooling the turbo bearings itself.

You are right.

Originally Posted by Optimus7

The compressed air is cooled down sufficiently by the inter cooler to make it denser, resulting in more power. Doesn't it help in cooling down the turbo (I am not sure though)?

No it doesnt. but your first sentence is right.

[ANUJ GEORGE]

@Thoma: I guess the proper name for these are after coolers. Due to the close proximity to the exhaust turbine & compression, the turbo charged air will have very high temperature. The after coolers take care of it.

[zipperone]

so then even cars with the intercoolers need to be idled for the minute

[dhanushs]

Originally Posted by Optimus7

Intercooler makes sure your turbo is cooled down sufficiently even after engine is switched off

Originally Posted by zipperone

so then even cars with the intercoolers need to be idled for the minute

Hi,

Intercooler has nothing to do with idling-for-a-minute turbos.

Turbo chargers run at high speeds.. so.. even after switching off the engine (while in turbo spinning range of rpms), inertia keeps the turbo spinning. But then, we know that the oil circulation stops as soon as we switch off the engine. Hence for the last ~30 seconds or so, the turbo spins without any oil circulation, and we know that is not good.

That is why we idle for a minute, as while idling turbo boost is not there, and the circulating oil can cool the turbo down, even if its spinning in its own inertia.

Intercoolers on the other hand is not related to turbo, its lubrication or cooling. They just cool the hot compressed air from the turbo.

[dadu]

The problem is more than the cooling of the turbo's as most turbo manufactures provide sufficient oil flow to the bearing in their designs. However, the extremely high temperatures that the turbo creates will cause the oil in the bearing loose its viscosity and lubricating qualities and cause coking in the turbo bearing housing. Over time this coking will restrict the flow of oil to the bearing leading to its failure.

The turbo's high temperature cannot be cooled with a 30sec or 1 min idle, actually the oil needs to flow at low boost pressure for atleast 15min, just like the coolant for your engine, to cool down the turbo bearing without restricting flow and coking.

Another help can be the engine oil, change it at regular intervals and with high temperature stability which comes in high Viscosity Index base oils. Also do not use engine oil with wide multi-viscosity range.

[zipperone]

Which oils are recommended for use with a diesel turbo? Are synthetic oils with a wide viscosity range better in this case? It seems that none of the oil brands markets any specific oil for use with turbo engines and mercedes, porsche and bmw etc recommend mobil 1 synthetic. Is this correct?

[Sutripta]

Originally Posted by Optimus7

Intercooler makes sure your turbo is cooled down

As others have said, no.

Originally Posted by dhanushs

That is why we idle for a minute, as while idling turbo boost is not there, and the circulating oil can cool the turbo down, even if its spinning in its own inertia.

Essentially cooled by the now much (relatively) cooler exhaust gases. This 1 min idling precaution is for the case where just prior to that, one has been running at close to full power.

Originally Posted by dadu

The turbo's high temperature cannot be cooled with a 30sec or 1 min idle,

Any hard data?

Regards
Sutripta

[shankar.balan]

It's not different really
It's just that all the newer ones don't have that sticker
The fact that it is recommended to idle a bit etc is mentioned in the manual

[thoma]

Originally Posted by dadu

The turbo's high temperature cannot be cooled with a 30sec or 1 min idle, actually the oil needs to flow at low boost pressure for atleast 15min

Nobody would be ready to idle for 15 min! I wonder then what happens to the turbos of Scorpios with micro-hybrid technology as mentioned below.

Originally Posted by mpksuhas

Another thing is Micro Hybrid Scorpios switch off temporarily when standstill for 5 Secs (?) to save fuel. Iam not sure how the one min thing works in this case.

Why doesn't the manufacturers provide something like turbo timers? Or are they of no good? One other technique I came across in another thread is, an oil reservoir that stores oil when the engine is running, and supply the oil at a pressure to the turbo when the engine is shut off. Is this not a good idea?
http://www.team-bhp.com/forum/techni...ml#post1679095

[bejoy]

There has been lot of innovation happening in the turbo bearings and making it less dependent on oil lubrication. Ceramic ball bearing is used in Honeywell/Garrett tubos and they don't seem to be idled during cold starts.

Checkout this link:
Honeywell Turbo Technologies » Ball Bearing


Turbos in each car are different - in terms of technology , so best bet is to follow the owners manual. Also the turbos are robust these days and they seldom fail.

[TaurusAl]

Originally Posted by srikanthns

I have question: I have a Ritz VDI. Due to traffic on the route, the engine RPM never goes beyond 1700.1800, means I never go into turbo range at all. If that is the case, still the idling befor switch off is to be carried out? PL clarify.

But I hear a whistling sound from the engine even at 1.5K RPM of my Ritz VDi. The whistling sound is of turbo if I'm not mistaken. Experts, correct me if I'm wrong.

[Optimus7]

Thanks Dadu, Dhanush, Suprita, so the Inter cooler is there only to increase the power boost. I think most modern cars comes with an Inter cooler, is it possible to fit an inter cooler in a turbo charged car, which doesn't have one?

[dadu]

Originally Posted by Sutripta

Any hard data?

Regards
Sutripta

No hard data, couldn't find any on it or on the manufacturers recommendation on the what , how and why of the Turbo temperatures and its impact on bearings beyond the basic sense we all have.

Originally Posted by Optimus7

Thanks Dadu, Dhanush, Suprita, so the Inter cooler is there only to increase the power boost. I think most modern cars comes with an Inter cooler, is it possible to fit an inter cooler in a turbo charged car, which doesn't have one?

Yes, by cooling the air and making it denser before burn.

It is possible but you will need to do a lot of homework on the plumbing, boost, Turbo lag etc, I suggest turbobygarrett website for more expert & precise calculations on it.

[1self]

Guys,

Dadu has already explained in post No.80 & to that let me add.

1. Intercooler has NOTHING to do with turbo & idling. The sole function of the intercooler is cool air charge down as much as possible to 1. Avoid detonation in petrol cars & 2. To give more power in both petrol & diesel cars.
Gas Laws (as was taught in school) states that if you compress any gas, all other properties being equal, the temperature of the gas will increase. Now depending upon the efficiency of the turbo (max 70%) more & more of the gas is heated up to higher temperatures. It is not uncommon that on a hot day, in traffic, the air coming out of the compressor at 1 bar pressure is almost 100 degrees celcius! The intercooler brings this temperature down.

Now, turbos which have an oil & water cooled central revolving assembly are much better off in the cooling department simply because they have 2 sources of cooling simultaneously. These are also ball bearing turbos so they, by superior design, produce less heat as they operate.

Most diesel turbos are oil cooled sleeve bearing turbos. It is with these that the idling-after-running-hard rule comes into significance. As dadu mentioned, coking is liable to occur when a hot turbo is not sufficently cooled & the engine stopped. Coking is a process of 'burning' of lubication oil which breaks down oil into carbon & other sticky substances. This prevents the flow of oil through the narrow & fine orifices, which results in a much-shortened life of the turbo bearings.

[rajni]

Originally Posted by TaurusAl

But I hear a whistling sound from the engine even at 1.5K RPM of my Ritz VDi. The whistling sound is of turbo if I'm not mistaken. Experts, correct me if I'm wrong.

Although I am not an expert on this I don't think your problem has something to do with this problem. I have had similar issue with my old Petrol Swift, which obviously doesn't have a Turbo an got it resolved at the Service station. The reason given by the service folks was dust particles deposited at the fan belt or clutch plates - can't correctly remember.

By the way, since this thread was started a few years ago I hope things would have changed a lot. I recently bought my first diesel car - Skoda Rapid. Any ideas if the idling is applicable to this car also.