Where the turbo starts boosting (engine revs) will change with its size, because the bigger the exhaust turbine, the faster the engine has to turn to make the turbine turn above idle, never mind to achieve positive boost. The reason for having some form of "wastegate" is to stop the runaway effect where more boost -> more power -> more exhaust gas -> more boost -> more power... until the engine explodes!

The turbo is spinning all of the time, and it's boost increases as the exhaust gas speed increase. However, with the likes of the tdi70 the maximum boost is limited to a point where VW deems it necessary ie 1600rpm and by controlling the VGT vanes or wastegate it can keep the torque produced to a constant level up to 2800rpm. The TDi80 is not limited so early on so goes on to produce more torque at a higher rpm (1800rpm), but still produces the same torque as the TDi70 at 1600rpm. It is then allowed to continue boosting longer than the TDi70 to produce the extra 10ps.....

Generally maximum boost is limited by engine detonation (knock),the air going into the compressor going supersonic at high engine rpm and stall at low engine rpm. Stall is when the energy given by the exhaust gas at low rpm cannot overcome the pressure in the inlet manifold causing the whole turbo to stop momentarily.

The wear on key components is highest at idle...

How can the wear on key components be at the highest when they are doing almost nothing?

Isn't the wear on components the highest under maximum acceleration, eg 0-60 drag race type situations? Or full throttle when the engine is cold?

I don't see how component wear is the highest when you sit in a traffic jam doing nothing???

How can the wear on key components be at the highest when they are doing almost nothing?

Isn't the wear on components the highest under maximum acceleration, eg 0-60 drag race type situations? Or full throttle when the engine is cold?

I don't see how component wear is the highest when you sit in a traffic jam doing nothing???

The wear on key components is highest at cold idle...

This is largely because component gaps are smallest, oil is circulating properly, andbore washing is highest.

I've recently heard that diesel engines do not warm up at idle and you need to drive away instantly to warm the engine up. As my 1.4 tdi 80 2 estate is on order I was wondering how diesel owners de-frosted their cars in winter in the past, or how they plan to in the next winter??? As I have no garage and leave for work at 5.25 am, I am a bit concerned!!!

The simple answer is defrost the windows start the car and drive off. You leave work 5 minutes before me and I don't have any trouble over winter.

1930

How can the wear on key components be at the highest when they are doing almost nothing?

Isn't the wear on components the highest under maximum acceleration, eg 0-60 drag race type situations? Or full throttle when the engine is cold?

I don't see how component wear is the highest when you sit in a traffic jam doing nothing???

Depends on the component.

I forget which part it is, but some of the timing and valve related parts are under more force when idling, especially when cold, than when being driven at higher revs.

I guess this is because there is a force on the part for longer rather than a brief on/off/on/off cycle when the engine is reving.

Depends on the component.

I forget which part it is, but some of the timing and valve related parts are under more force when idling, especially when cold, than when being driven at higher revs.

I guess this is because there is a force on the part for longer rather than a brief on/off/on/off cycle when the engine is reving.

If they're rotating shafts in bearings, I'd think it's because you're not evolving hydraulic film effects with thick cold oil and high or very low revs.

Metal, like everything else expands and contracts depending on temperature. When the engine is cold, everything is tight, add in the low oil pressure caused by idling and you get much more wear than with a warm engine thats loosened up because the metal has expanded.

Bassa, A diesel engine warms up much quicker under load. For my 2.0Tdi, I reach operating temp (90c) within 4 miles of leaving home/work.