[firstguri]

Ok, engineer to the rescue; that's me by the way

The basic thing is that turbocharger bearings are lubricated by oil. Heck, who thinks of water as a lubricant . Now water cooled turbochargers help in keeping the casing of turbochargers cool due to which the oil would not coke up. Also without getting too technical I would just like to inform that water cooling arrangement is such that it is natural and not force pumped. Basically the coolant heats up, expands, gets pushed out of the chamber and the vacuum created behind by this pulls in fresh coolant. So it's just basic physics. Now because of all this even if the engine is stopped when things are running hot, the natural circulation of coolant to the turbocharger casing continues and it'll prevent the oil in the turbocharger bearings (which is not circulating now) from overheating. Hence much reduced chances of oil coking up.

Being an engineer I always idle for some time, turbocharged or not, after a considerable drive not for turbocharger but to let the exhaust side of engine cool down. Again without getting into technicalities, just know that it's better for engine. But still if you want to know; it reduces the thermal stresses that the engine components will encounter after shut down.

[Metallicar]

Jetta 2.0 TDI manual asks the car to be driven as soon as possible without any idling. It mentions that it is better for the engine this way as the engine can reach its optimum temperatures in the fastest possible way.

While switching off - After a long drive you can idle it for 30 sec to a min. Sometimes even after switching off you may hear some components running. This is to ensure proper cooling off even after the car has been switched off.

[Tanveer_2558]

Originally Posted by Metallicar

Jetta 2.0 TDI manual asks the car to be driven as soon as possible without any idling. It mentions that it is better for the engine this way as the engine can reach its optimum temperatures in the fastest possible way.



While switching off - After a long drive you can idle it for 30 sec to a min. Sometimes even after switching off you may hear some components running. This is to ensure proper cooling off even after the car has been switched off.

Yes and car should be driven sedately and it warmsup quick enough, I recently also saw a detailed video which explained very well why should the car be driven sedately instead of just keeping the car idling after a cold start.

[Jeroen]

Originally Posted by Tanveer_2558

Yes and car should be driven sedately and it warmsup quick enough, I recently also saw a detailed video which explained very well why should the car be driven sedately instead of just keeping the car idling after a cold start.

Modern diesels and to some extent petrol engines too, are so efficient that they hardly warm up when just left to idle. A cold engine idling away does two things, it doesn't run very cleanly emission wise, but it also causes a lot of wear and tear notably on the cylinder liners and piston rings. So best to start from cold and drive away immediately, avoid high rpm and stressing the engine until its properly warmed up. Please note that the cooling water temperature is not a good indication. The oil temperature will lag behind by quite a bit.

Jeroen

[Tanveer_2558]

Originally Posted by Jeroen

Modern diesels and to some extent petrol engines too, are so efficient that they hardly warm up when just left to idle. A cold engine idling away does two things, it doesn't run very cleanly emission wise, but it also causes a lot of wear and tear notably on the cylinder liners and piston rings. So best to start from cold and drive away immediately, avoid high rpm and stressing the engine until its properly warmed up. Please note that the cooling water temperature is not a good indication. The oil temperature will lag behind by quite a bit.

Jeroen

And Exactly thats what i do with both my cars, And have been doing the same with my previous car's as well. Just driving sedately till the temperature needle has reached the half mark and we are good to go !

[Rahul Bhalgat]

Recently the fellow BHPian Styler faced a major problem on his 2004 Mahindra Scorpio with non CRDI TC mHawk engine.

Apparently, the sequence of events was:

• For the first few years, the idling rule was followed strictly. After that, it was not followed strictly. Otherwise, the engine and the Scorpio has been maintained properly.
• During the last service, the oil was found leaking in the turbocharger. The SA told Styler that he could let it continue and it would do no harm! So, it was left as it is innocently.
• One day, Styler experienced engine runaway (engine accelerating without accelerator input) with heavy smoke in the middle of the road. The engine had to be opened, the cylinder head, all the four cylinder liners, one piston, two valves along with valve guides and push rods had to be replaced. The turbocharger too had to be replaced.

Here is a link to Styler's post:
http://www.team-bhp.com/forum/techni...ml#post3875854

The explanation of the phenomenon:

• The engine oil burns through compression in a diesel engine, like a regular diesel fuel.
• If the idling rule is not strictly followed, the turbo bearings and seals will be damaged eventually and they may will leak oil into the turbo.
• If turbo is leaking the lub oil on the intake side, this oil will go into the cylinder and burn in the engine, along with the injected diesel.
• This will increase the engine rpm even in absence of accelerator input and in turn increase the lub oil flow rate.
• That will send even more lub oil into the engine and further increase the engine rpm.
• This vicious circle will cause runaway.

Here is a link to an article containing detailed information about engine runaway caused by TC oil leakage:
http://www.myturbodiesel.com/wiki/di...and-repair-it/

[Jeroen]

Its an interesting article, however I don't think there is a real correlation with the practice of idling (or not for that matter).

Jeroen

[KkVaidya]

Originally Posted by Rahul Bhalgat

Recently the fellow BHPian Styler faced a major problem on his 2004 Mahindra Scorpio with non CRDI TC mHawk engine.

• If the idling rule is not strictly followed, the turbo bearings and seals will be damaged eventually and they may will leak oil into the turbo.

This could be very true with Mahindra vehicles and that is why they paste the "Yellow Idling rule sticker" near the instrument cluster binnacle.
I have seen a 2.6 Scorpio CRDe emit heavy smoke after years of service @ more than 2 lakh kms before it was sold-off. The idling rule was never followed by the driver.

[Rahul Rao]

I have seen bigger engines (generator) run away, infact I have a video of a railway engine in run away mode.
When engine runs away it is burning the engine oil, and as the oil pump is feeding oil it will remain on till it runs out of oil. In such a case to prevent other items like bearings pistons liners etc from running out of oil and ceasing up you have to stall the engine. Push the car upto a wall touch it, shift to highest gear, and slowly release clutch till engine stalls.
For generators load applied on it is increased till it stalls. The building where it occurred they had to connect all possible loads there till it stalled.

Rahul

[anand.shankar]

Originally Posted by Rahul Rao

I have seen bigger engines (generator) run away, infact I have a video of a railway engine in run away mode.
When engine runs away it is burning the engine oil, and as the oil pump is feeding oil it will remain on till it runs out of oil. In such a case to prevent other items like bearings pistons liners etc from running out of oil and ceasing up you have to stall the engine. Push the car upto a wall touch it, shift to highest gear, and slowly release clutch till engine stalls.
For generators load applied on it is increased till it stalls. The building where it occurred they had to connect all possible loads there till it stalled.

Rahul

A dumb question:

Why cant one turn the ignition off instead of using the wall ?

[Rahul Bhalgat]

Originally Posted by anand.shankar

A dumb question:

Why cant one turn the ignition off instead of using the wall ?

Turning off the ignition will cut off the fuel supply of the running engine. But the engine will continue to run on the lub oil !

The phenomenon is stated in this post:
http://www.team-bhp.com/forum/techni...ml#post3881873

In petrol engine, when we turn the ignition off, the spark plug does not get the current and the sparking stops. So the fuel cannot burn and the engine stops.

The diesel engines run on compression ignition; no external spark needed. We stop the engine by cutting it's fuel supply. So, in case of a runaway, they continue to run using the lub oil.

[Rahul Rao]

Another way to stop a run away engine is to choke it. IE block the air intake , at times there is leakage in the intake, and even blocking it doesnt allows air to leak in and it may not stop. Even then lack or lower supply of air may atleast slow it down making it easer to stall, this is especially true with generators where run away engines reve beyond normal RPM, and generate at a frequency higher than what the load can sustain.

Rahul

[anand.shankar]

Originally Posted by Rahul Bhalgat

Turning off the ignition will cut off the fuel supply of the running engine. But the engine will continue to run on the lub oil !

The phenomenon is stated in this post:
http://www.team-bhp.com/forum/techni...ml#post3881873

In petrol engine, when we turn the ignition off, the spark plug does not get the current and the sparking stops. So the fuel cannot burn and the engine stops.

The diesel engines run on compression ignition; no external spark needed. We stop the engine by cutting it's fuel supply. So, in case of a runaway, they continue to run using the lub oil.

Thanks, that explains, and quite scary situation if one isnt aware of this situation! May be another way to stall might be to slot the car into top gear 5th/6th directly from stand still, guess that should be enough to stall any small diesel engines.

[Rahul Rao]

Originally Posted by anand.shankar

May be another way to stall might be to slot the car into top gear 5th/6th directly from stand still, guess that should be enough to stall any small diesel engines.

No it is not enough, the diesels have enough torque to move the car ahead even while starting in the highest ratio. You have to do that with the front pressed against a strong barrier, preferably a column, or rock side wall of a mountain side. I guess oil has more calorific value than diesel.

Rahul

[auto_enthusiast]

Originally Posted by Rahul Rao

No it is not enough, the diesels have enough torque to move the car ahead even while starting in the highest ratio. You have to do that with the front pressed against a strong barrier, preferably a column, or rock side wall of a mountain side. I guess oil has more calorific value than diesel.

Rahul

Instead of pressing the car against a wall or column, can't we stall the engine by applying brakes and releasing the clutch while the car is engaged in a gear. That way it will be much easier as well as damage free too