[Jeroen]

Originally Posted by vharihar

I am no auto/mech engr, but my gut feel told me all these days that the engine rpm is a *proxy* for the "loading", by means of the transmission. In other words, whether you end up revving the engine at 2500 rpm by driving in the 5th gear at 90 kmph, or at the same 2500 rpm by driving in the 3rd gear at 40 kmph, I thought that the engine loading was the same in both cases (since the rpm is the same).
.

On cars the engine RPM do not say much about how much power the engine is generating perse. An extreme case, think about diesel generators. They run at constant RPM and generate from idle load to max load all at the same RPM.

The actual loading of an engine is a result of the engine having to overcome resistance. During acceleration it is more about having to accelerate a force obviously. But at a steady pace driving it is about overcoming resistance. By far the greatest one is air resistance. If you drive at 2500 RPM in first gear your car might be doing 15-20 km/h if that. At those speeds air resistance is very very small. But you do 2500 RPMin fifth gear you are likely to be doing 90-110 km/h. Air resistance is exponentially higher. What it means at the very same RPM of the engine is loaded up considerably more. (And thus much higher exhaust gas temperature

Originally Posted by Rahul Rao

@vharihar.
Actually with low load engine is running at lower compression l

Compression or rather compression ratio is fixed on an engine (well almost any engine). The compression ratio is determined by the cilinder diameter and the stroke of the piston. They are, obviously, fixed.

The actual compression can be to some degree influenced by valve timing. The actual compression only starts when both valves are closed.

Especially on turbo engine the intake air is somewhat compressed (by the turbo) that means it is also warmer as it enters the engine and it has a higher density. When you compress warmer air, the final compression pressure and temperatures will go up as well, compared to colder air. The higher the load the higher the inlet air temperature and air density.

(It is one of the reasons most turbo engines will have somewhat lower compression ratio’s compared to none turbo engines. or even intercoolers)

Jeroen

[Rahul Rao]

@Jeroen
The physical compression ratio is fixed. But the turbo boost varies depending on many factors. If you are going down hill in gear without touching the throttle, the air entering engine is reduced, as (in fixed geometry turbo waste gate is bypassing the turbo) and in VGT the vanes are in to push in far less air.

Along with this no or negligible amount of diesel is being injected.


Rahul

[Jeroen]

Originally Posted by Rahul Rao

@Jeroen
The physical compression ratio is fixed. But the turbo boost varies depending on many factors. If you are going down hill in gear without touching the throttle, the air entering engine is reduced, as (in fixed geometry turbo waste gate is bypassing the turbo) and in VGT the vanes are in to push in far less air.

We are discussing ways to cool down the turbo. Boost pressure is not a good measure for what is happening on the turbine side of the turbo. That is where the hot exhaust gasses are. Engine load has a direct correlation on the exhaust temperature.

There is of course some correlation between boost and exhaust temperature and volume of exhaust air. But with waste gates it is way more complicated. Heck, even without a waste gate it is more complex.

If you want to know how long you need to cool down a turbo, you need to know how hot the turbine is. Which is directly related to exhaust gas temperature and how long that has been going down that turbine. Cooling down, same thing, how much air at how much temperature determines how much and how fast you cool it. All down to engine loading, nothing else really.

But to put your comments to practical use:

If you own a turbo engined car, make sure your house is at the bottom of a hill, so you can essentially coast home the last few kilometers. You will never ever have turbo problems!

Jeroen

[Rahul Rao]

Originally Posted by Jeroen

But to put your comments to practical use:

If you own a turbo engined car, make sure your house is at the bottom of a hill, so you can essentially coast home the last few kilometers. You will never ever have turbo problems!

This is something I always do.

I'm half way up a gradient, so I always return home from the the higher side with engine idling in a mid gear. In fact I don't have to touch the throttle for over a minute when I approach or depart from my home.

I have never faced turbo issue even in cars as basic as 2005 Indica turbo whose engine lasted till car was sold after use of 3.24 Lakh km.

Even the retrofit turbo in my Dad's 1989 Contessa lasted from 1993 to 2004.

Rahul

[shashanka]

Originally Posted by Jeroen

......Initially there were some concerns whether these self contained system would be able to ensure sufficient lubrication when the engine was switched off. Due to over pressure in engine rooms, the turbo’s tended to spin, slowly but surely, on differential pressure between the engine room and the outside.....Jeroen

Perhaps I am ill-informed - and it would be interesting to know the source of these "initial concerns", since I have yet to come across / read about an example (post late-60's, since I stepped on board my first vessel in 1973) incorporating both the gravity feed system & also the self-contained lub. system for T/C emergency lubrication. It would almost appear to be a case of over-kill!

[haridsv]

My house is at the end of 0.5km society roads where I can't drive more than 20kmph, so I mostly just cruze in first gear (except for a couple of speed bumps where I press clutch and accelerate momentarily). This means, for about 1.5min both at the beginning and at the end of my drive, I drive very slow. I haven't been following the idling rule so far but now that I came across this thread, wondering if I should add it to my schedule or if my current 1.5min routine is sufficient. I drive a 2012 Ford Figo Diesel.

[Reinhard]

Originally Posted by haridsv

My house is at the end of 0.5km society roads where I can't drive more than 20kmph, so I mostly just cruze in first gear (except for a couple of speed bumps where I press clutch and accelerate momentarily). This means, for about 1.5min both at the beginning and at the end of my drive, I drive very slow. I haven't been following the idling rule so far but now that I came across this thread, wondering if I should add it to my schedule or if my current 1.5min routine is sufficient. I drive a 2012 Ford Figo Diesel.

What you are doing right now is good enough for cool down. You are driving since 7 years without issues, so its working well.
However - do spend at least the same amount stationary for cold starts. Without any movement or coasting towards the gate. During warm up, its necessary for the oil to circulate well in the turbo, transmission & cylinders. Helps to let the engine warm up with no transmission load (moving the car).

[ds.raikkonen]

I follow this rule even with my NA vehicle
Actually cringe whenever my neighbours drive off immediately after starting their vehicles in the morning!

[Jeroen]

It is better for any engine to drive of straight away. Engines, especially diesels do not warm up whilst idling. Most wear occurs just after cold start. With the oil cold and the cylinder lining cold, the oil will not work well, causing wear of the piston rings and cylinder.

Oil circulation starts immediately at engine start. You do not have to wait 20-30 seconds for it to reach all parts.

The best practice is to start the engine and drive away cautiously. Try not to rev or to load up the engine during the first ten minutes. If your car has a cooling liquid temperature gauge; after it shows normal operating temperature add another five minutes for the oil to reach normal operating temperature.

Or you could go really whacky and see what your owner manuals states!

Jeroen

[a4anurag]

Originally Posted by Jeroen

The best practice is to start the engine and drive away cautiously. Try not to rev or to load up the engine during the first ten minutes. If your car has a cooling liquid temperature gauge; after it shows normal operating temperature add another five minutes for the oil to reach normal operating temperature.

This is precisely what I've been following since long as letting a 'cold engine' idle will cause more harm than good.

This is what the owner's manual says (Hyundai):

[Pancham]

Originally Posted by a4anurag

This is precisely what I've been following since long as letting a 'cold engine' idle will cause more harm than good.

This is what the owner's manual says (Hyundai):
Attachment 1946063

But for turbo charged engines the Hyundai manual does ask you to idle after cold start, right ? What am I missing here ?

[a4anurag]

Originally Posted by Pancham

But for turbo charged engines the Hyundai manual does ask you to idle after cold start, right ? What am I missing here ?

You can idle for 10-15 seconds but no need to idle for longer. Better to drive off slowly without letting the turbo spool till the engine reaches operating temperature.

[BigBrad]

Here's what the VW manual says:

Link (Why you must practice the "Idling Rule" with Turbo-Charged Cars)

[shankar.balan]

Originally Posted by Jeroen

It is better for any engine to drive of straight away. Engines, especially diesels do not warm up whilst idling. Most wear occurs just after cold start. With the oil cold and the cylinder lining cold, the oil will not work well, causing wear of the piston rings and cylinder.

Oil circulation starts immediately at engine start. You do not have to wait 20-30 seconds for it to reach all parts.

The best practice is to start the engine and drive away cautiously. Try not to rev or to load up the engine during the first ten minutes. If your car has a cooling liquid temperature gauge; after it shows normal operating temperature add another five minutes for the oil to reach normal operating temperature.

Or you could go really whacky and see what your owner manuals states!

Jeroen

How should I treat my second hand Mini Cooper S Turbo Petrol R56 2012 model at startup and stop time?

1. Should I start and idle for 30 sec or not?
2. When I stop even if I ve been driving sedately, should I idle for 30 sec and then switch off or not?

Because all these years with all the Turbo Diesel cars I ve had, I ve always diligently followed this idling rule for 20-30 seconds every time before starting and/ or stopping.

[Jeroen]

Originally Posted by shankar.balan

How should I treat my second hand Mini Cooper S Turbo Petrol R56 2012 model at startup and stop time?

1. Should I start and idle for 30 sec or not?
2. When I stop even if I ve been driving sedately, should I idle for 30 sec and then switch off or not?

Because all these years with all the Turbo Diesel cars I ve had, I ve always diligently followed this idling rule for 20-30 seconds every time before starting and/ or stopping.

You should read the owner manual and follow to the letter.

Jeroen