[Rahul Rao]

Originally Posted by sgiitk

One thing which foxes me. Many cars (Diesels are almost invariably Turbocharged) come with start-stop technology. Now the engines shut down at the drop of a hat. So how does the slow shut down strategy work in those.

Sorry for replying after such a long time, I got to experience a lag in auto stop yesterday, and remembered your question.
I was driving a friends X3 with its 8 speed ZF auto from city speeds to country road speeds upto 80-90, the car was shifting and maintaining just between 1200 to 1600 rpm. At every dead stop the engine was shutting down, and as soon as I got my foot of the brake, and touched the accelerator it was restarting.
At one point I was following a convoy of truck at low speeds on NH 66 (Old NH17), and as soon as I saw a opportunity, floored and overtook 4 trucks reaching 100 in a low gear with RPM above 3000, as I was comming up onto a curve, I slowed and got back into my own lane with 2 trucks from the group ahead of me.
suddenly the traffic came to a dead stop, due to another overtaker from the opposite side not getting back into his lane in time, and blocking the lead truck, I was at dead stop but the engine remained on for about half a minute and then stopped.

Rahul

[debuda]

Originally Posted by Rahul Rao

suddenly the traffic came to a dead stop, due to another overtaker from the opposite side not getting back into his lane in time, and blocking the lead truck, I was at dead stop but the engine remained on for about half a minute and then stopped.

Rahul

Very useful information. Clearly establishes that intelligent stop/start systems don't stop the engine immediately after it has been used at higher power levels but cater for some cooling down time. Also makes it clear that in normal slow speed driving in city traffic no cooling down is required by modern engines / turbos.

[el lobo 6061]

In diesel cars equipped with Start/Stop e.g. BMW X1, it tends to turn off as soon as you come to a halt 99% of time. In that case would 1 minute idle rule become void?

How does the system function differently in these cars compared to traditional cars

E.g. VW Vento TDi where you idle car for 1 minute before turning it off.

[Nikhilb2008]

Originally Posted by el lobo 6061

In diesel cars equipped with Start/Stop e.g. BMW X1, it tends to turn off as soon as you come to a halt 99% of time. In that case would 1 minute idle rule become void?

How does the system function differently in these cars compared to traditional cars

E.g. VW Vento TDi where you idle car for 1 minute before turning it off.

In most new cars, there is a fail safe mechanism to prevent any engine/turbo damage due to the start-stop

If the engine management system which is monitoring all temperatures feels that it's too hot(or too cold), it wont switch off the engine. It will switch off the engine only when it feels it's safe to do so.

Also, in most new cars, the engine being switched off doesnt mean the water pump will also switch off. The water pump continues to run and circulate coolant through the engine, turbo, etc. So, the process of cooling the critical parts of the engine continues.

On my vRS, I hear a slight hum even when the engine is switched off... It stops after a few minutes depending on how hard I've been on the car.

[Chethan B G]

Originally Posted by Nikhilb2008

Also, in most new cars, the engine being switched off doesnt mean the water pump will also switch off. The water pump continues to run and circulate coolant through the engine, turbo, etc. So, the process of cooling the critical parts of the engine continues.

On my vRS, I hear a slight hum even when the engine is switched off... It stops after a few minutes depending on how hard I've been on the car.

Water cooled Turbos are predominantly used in recent turbo-charged petrol engines. Exhaust gas from Petrol engines are much hotter than Diesel engines as the air-fuel mixture is richer; un-burnt fuel is higher in a petrol engine as the air intake is limited by throttle. Also, for the Petrol engine, higher boost pressure is needed and so, the turbo spins a lot faster. Because of these reasons turbo turbo heats up more. Forced water cooling keeps the turbo safe.

In case of the Diesel engines, now a days, there are self lubricated turbos which decreases the chances of oil coking. Also the use of ceramic ball bearing, enhances the life and efficiency of a TC.

[Sankar]

Al Innova Crystas and Fortuners with the new GD engine has water cooled turbos, but the water pump is engine driven. Compared with the previous gen engine KD the turbo of GD spins at about 100,000RPM more.

Owners manual asks to let it idle before shutdown if coming in after high speed drive.

[el lobo 6061]

Originally Posted by Nikhilb2008

On my vRS, I hear a slight hum even when the engine is switched off... It stops after a few minutes depending on how hard I've been on the car.

Same thing on X1. Drive it in Sports mode and post turning off the car; you hear the hum noise as described above for cooling engine.

Any idea BMW 20d engine has water cooled or oil cooled turbo charger?

[Chethan B G]

Same thing on X1. Drive it in Sports mode and post turning off the car; you hear the hum noise as described above for cooling engine.

Any idea BMW 20d engine has water cooled or oil cooled turbo charger?

Hum noise is from the radiator cooling fan.

X1 F48 B47 has a self lubricated VGT from Garrett with ceramic ball bearing.

Turbo is oil cooled. Turbo life is claimed to be similar to the life of the engine, which is claimed to be 10L Kms.

X1 F48 B48 Petrol engine sold in USA has a water cooled turbo and electrical coolent pump. This pump is independent of the engine and runs for sometime even after the engine is shut off.

[sgiitk]

Originally Posted by Rahul Rao

suddenly the traffic came to a dead stop, due to another overtaker from the opposite side not getting back into his lane in time, and blocking the lead truck, I was at dead stop but the engine remained on for about half a minute and then stopped.

Half a minute before shutting down - excellent. I hope this is the norm. Half a minute is enough to allow the turbo to cool down.

[Rahul Rao]

Originally Posted by el lobo 6061

In diesel cars equipped with Start/Stop e.g. BMW X1, it tends to turn off as soon as you come to a halt 99% of time. In that case would 1 minute idle rule become void?

I guess that it is probably the 1% time it does not shut off immediately when the ideling is necessary. Rest of the time it is probably not needed.

Originally Posted by el lobo 6061

How does the system function differently in these cars compared to traditional cars.
E.g. VW Vento TDi where you idle car for 1 minute before turning it off.

In a traditional car you dont know the temperature of the turbo, nor do you know what RPM it is spinning at.
I have not followed the practice of 1 min ideling as a regular feature, rather I have driven with engine below 1400RPM for first 2 km and last 1 km or so before stopping. Till date I have not faced a turbo issue, usage of cars as below (2005 Indica turbo 3.24 lakh km, Innova 1.9 Lakh km, Tavera 1.7 Lakh km, Polo 79k km damaged in accident).
After zesty driving on a highway I have idled for far more than a minute until the sound of engine has softened.

Rahul

[el lobo 6061]

Originally Posted by Chethan B G

Turbo is oil cooled. Turbo life is claimed to be similar to the life of the engine, which is claimed to be 10L Kms.

During a start/stop when the engine turns off, will the turbo be supplied oil to cool down or how does it work?

[Chethan B G]

Originally Posted by el lobo 6061

During a start/stop when the engine turns off, will the turbo be supplied oil to cool down or how does it work?

During auto start/stop, ECU checks several parameters such as Battery charge, Interior/exterior temperature, Engine oil temperature.. etc; and then shuts of the engine if all the parameters are within permissible limits. If one of the parameters are not within tolerance, the engine will not shut-off.

Oil pump is driven by the engine and will not run when the engine is shut-off. The plumbing line above the TC will act as a reservoir and continue to supply oil to the TC due to gravity, which aids cooling; this is taken care by design.

Oil is used only for cooling the Turbo block and not for lubrication as in case of older TCs. This TC is of self lubricated type with ceramic bearing. Therefore, the problem of oil coking around the bearing is avoided. This used to be the main cause of TC failures.

The ECU shuts off the engine only if the car has exceeded 7 KMPH speed before complete stop. This threshold is very low and is the main cause of irritation in B2B traffic, as the engine tends to go off very often. IMO, if this threshold is set to say, 30 KMPH, it can be practical for Indian conditions. Will have to find a way to code this!

Please check these links below. You may find them interesting:

https://turbo-diesel.co.uk/product/t...k-new-garrett/

http://www.wcengineering.com/articles/dieselturbo.html

https://www.turbobygarrett.com/turbo...tt/why_garrett

[Chethan B G]

Originally Posted by Sankar

Al Innova Crystas and Fortuners with the new GD engine has water cooled turbos, but the water pump is engine driven. Compared with the previous gen engine KD the turbo of GD spins at about 100,000RPM more.

Owners manual asks to let it idle before shutdown if coming in after high speed drive.

Even though the water pump goes off, the water will continue to circulate albeit slowly for a short while due to Thermo siphon effect. This can further cool the turbo housing.

[unstoppable]

Hi Petroheads,

A quick question "Is turning an engine on for a min or so is the thing of the past?". The only reason I am asking this is because I am of a thought that it will help the oil to circulate properly withing a min+ and then we can ride ahead.

But I have few people who say that its the thing of the past and as of today the engines are much more efficient and refined (which I do agree by the way) but does that change the very basics of idiling and then take off. Kindly educate me. By the way I ride Polo GT.

Regards

[Simhi]

Some of the threads you can refer to

https://www.team-bhp.com/forum/techn...-vehicles.html (Idling Time during Morning Start for MPFI Vehicles)
https://www.team-bhp.com/forum/techn...rged-cars.html (Why you must practice the "Idling Rule" with Turbo-Charged Cars)

Mods, kindly merge this thread with appropriate one