How to keep that turbo pumping for longer

In a normally aspirated engine, breathing (by which I mean the intake of a fuel/air mixture) is a function of atmospheric pressure.  That is why such cars lose performance at high altitudes – the pressure is lower than at the coast and there’s less oxygen in the air –  such that in Harare, power outputs are reduced by around 15% on manufacturer’s claims.
A turbocharger, which in simple terms consists of a shaft with an exhaust driven turbine attached to one end and a compressor wheel to the other, stuffs more air into the engine which in turn means more fuel can be added to the denser air  intake.   All this adds up to greater fuel burning efficiency which liberates more power and torque.  It also means that altitude becomes much less of a negative factor but all is not sweetness and light.
When you compress air, you introduce heat.  Just feel the outlet pipe on a common garage air compressor or even a bicycle pump and you’ll get some idea that when the air is compressed, it gets rather warm.  It gets warmer still when red hot exhaust gases are involved in the process to the extent that air exiting a turbo housing can reach temperatures around 200C.  Now it stands to reason that hot air is less dense and it can lead to alarmingly high combustion temperatures within the engine itself.   Lower density also tranlates into lower power because to maintain a near-ideal fuel/air mixture, less fuel can be added to the mix.
 
The solution lies in diverting the pressurised air through an intercooler which in simple terms is a heavily finned radiator which is cooled by passing air or by circulating water.  In the meantime, at full chat the turbo shaft can rotate at up to 170 000 times a minute in bearings located in a housing which glows red hot when viewed at night.  The shaft and its bearings situated at either end are totally reliant on engine oil  to survive the searing environment (some turbo housings are also cooled  after shut down by water diverted from the engine cooling system) which tells you that the quality of the oil and its cleanliness is absolutely critical to the survival of this relatively simple power-boosting device.
So, given the incredibly hostile environment that a turbo works in, what can you do to maximize its life?   To answer the question, we need to look at those conditions that are especially detrimental to long life and in no particular order, these are excess heat, dirt, incorrect lubricants and overspeeding.   The last mentioned factor is thought  to be an issue in persistent turbo failures on certain models and makes of car operated on the Gauteng highveld.  I think here of early models of the BMW320d which suffered from regular warranty claims covering turbo issues which had clearly not been detected during BMW’s thorough testing.  It is thought the thinner atmosphere of the highveld allows the turbine shaft to run at speeds beyond the design ideal and presumably, the lubricating oil can’t cope with the additional heat generated.
To be fair to BMW, it wasn’t just their model that was affected but one must assume that steps have been taken by all manufacturers to address this specific problem or the affected models would have to be withdrawn from sale.  Interestingly, I have run a number of turbo cars, petrol and diesel, in Harare (which coud also be classified as a high altitude location) and have never experienced the slightest problem but that could related to issues that follow.
Because of the speed at which it rotates and because of the expansion/contraction issues created by massive temperature changes, it stands to reason that precision is the order of the day in the manufacture and assembly of the turbo internals which rely on a film of oil as thin as six to nine microns to maintain metal separation and provide some cooling effect.   While you cannot do much about heat generated during the course of driving other than to back off the throttle, you can massively influence the temperature of the turbo housing when you shut down the engine.  This is the single most controllable issue in the quest to maximise service life and what it translates into is the absolute need to idle the engine before  its turned off. 
The story here is that if you switch off immediately, especially after a long run or operation at full load such as climbing a hill, the massive heat surrounding the shaft bearings “boils off” the lubricant and in the most simplistic terms, leaves behind abrasive carbon deposits.  Each time you start the car, the abrasion gnaws away at the shaft and its bearings until the turbo wears out, either through bearing failure which would cause catatrophic shaft seizure, or through oil escaping past the turbo seals or through the effects of imbalance caused by the shaft floating in its bearings.Whatever anyone might claim to the contrary, you MUST idle the engine for up to three minutes after a long, hot run or for at least a minute in urban use, before you shut down.  The reason for doing this is that exhaust gas temperatures drop massively at idle (even if water temperature rises because of the lack of airflow through the radiator) and the flow of oil through the bearings takes away even more heat, so avoiding the aforementioned oil degradation problem.
All this rather logically points to oil quality being another prime issue and it sure is.  I know it’s difficult in Zim to source the best oils but don’t take short cuts on this matter.  Make a point of finding and using fully synthetic oils if your vehice is turbocharged.  Such lubes maintain their operational values with much greater consistency over a wider heat range and are especially resistant to heat degradation which is a known turbo potential achilles heel.  If the fuel is diesel, then make an effort to find a synthetic oil specifically formulated for use in diesel passenger car engines as opposed to diesel commercial vehicle engines which have different needs owing to their massive sump capacity and differing operational conditions, not least of which is a much lower rev regime.  The “diesel” engine oils are designed to keep soot (a by-product of incomplete diesel combustion)  in suspension so as to avoid clogging of oil lines, a factor which will see off a turbo in minutes.  It therefore stands to reason, whether you’re talking petrol or diesel, that regular oil and filter changes are crucial.
Finally, damage can easily be caused to the turbine by the ingress of dirt or other particles.  Even the smallest amount of imbalance caused by blade damage can cause rapid failure of a turbo, so ensure your air filter and its housing are kept really clean, especailly in the case of diesel engines.   Abide by these simple caveats and you’ll enjoy the benefits of  extended turbo life which can mean 200 000 kms or more without any attention being needed.

World Car of the Year
Amidst all the gloom and doom surrounding the floundering US auto industry, there was some excitement for one manufacturer at the New York International Motor Show when the identity of the 2009 World Car of the Year was announced.  In a competition judged by 59 auto journalists selected from 25 countries around the world, the winner was the Volkswagen Golf 6.
This honour for Volkswagen is surrounded in irony for the simple reason that when the Mark 6 version of the iconic hatchback was first revealed at last year’s Paris Motor Show, it was greeted with a chorus of doubting verbiage for the simple reason that it was not seen to be sufficiently different to the Mark 5.   The real reason for the somewhat early launch of the sixth iteration is that its predecessor was too expensive to build and that margins on the big seller were paper thin.  The latest model uses simpler construction methods that have brought build time somewhat nearer the main stream competition, but what couldn’t be easily detected at launch, is that under the skin of the apparently familiar new model, were a host of changes designed to improve economy, safety, performance, and most importantly, refinement levels.
Subsequent hands on reports in the mainstream motoring press have drawn rave reviews for the Golf 6.  Most reports, especially that produced by “What Car?” late last year, positively gushed about the new-found levels of serenity in terms of hushed ride and overall refinement, not to mention a standard of interior trim which has apparently lifted the mainstream Golf above many cars in the so called luxury class.   Now, the range has been boosted with the introduction of the decidedly enticing but typically solid GTI with 207 HP turbo motor, a package that has again had the press in raptures.
While I’m not necessarily a fan of car of the year competitions, this one does at least encompass a broad cross section of global opinion and for once, a car renowned for solid virtues rather than pizzazz, has attracted the plaudits almost certainly because it sets new standards in its class that the competition will be scrabbling to emulate.  If ever you wanted an example of not judging a book by its cover, the Golf 6 is clearly it. 
Astra Wanes
Sadly, GM South Africa has removed the once popular Astra model from its price lists in South Africa along with the Meriva and other less significant models.  This comes just as GM Europe has announced the introduction of a new Astra model.  Significantly, GMSA has seen fit to issue a press statement justifying its model range cut-back so clearly, there have been a few tongues wagging out in the market place.  One of the reasons given was the unfavourable Rand/Euro exchange rate but this is no different to the rate used by other competing manufacturers so you can put poor sales levels down as the main reason.  On a positive note, GMSA announced that the Chev Cruze, as featured recently in Top Gear, will be introduced in the third quarter of 2009.