I just bought a Golf TDi. I wanted a diesel for the obvious reasons – longevity and fuel mileage – but was suspicious about turbochargers. In my research I saw repeated reference to “turbo-lag”. Can you define that for me? – Paul in Sudbury, Ont.
I often refer to it as the difference between “ask” and “answer” – the time between when you press on the accelerator and the engine delivers. There were some situations where that was a noticeable and problematic delay of a second or more. The good news is you won’t find much, if any, of that with your TDi – good choice, by the way.
Turbochargers are devices that force more air and fuel into the cylinders – resulting in more power without requiring a larger engine. Think of them as having a couple of propellers at opposite ends of a shaft.
One end sticks into the exhaust stream where gasses forced from the engine during the regular combustion cycle spin that “propeller,” causing the one attached to the other end to spin as well. That one is in the intake system and the spinning motion forces more air/fuel into the engine.
When you step on the throttle, the engine speeds up and puts out more exhaust which spins the turbo, etc. It takes time for the “propellers” to get up to speed – as much as 100,000 rpm and this period of time is “turbo lag.”
Early turbochargers were large and heavy and it was not uncommon for it to take a period of time to get them up to speed. But engineers have devised a number of solutions involving electronics and, in some cases, two turbochargers to solve the problem. The twin-turbo approach involved a tiny little turbo that spins quickly and easily to get things started while the bigger one gets up to speed.
Your concern about reliability is justified because turbochargers spin so fast and the exhaust gasses make things incredibly hot. But again, solutions have been found thanks to electronics that continue to circulate cooling fluids (oil and sometimes coolant) through the turbo after the engine is shut down. The trick to long life is to follow the manufacturer recommendations for oil and oil changes.
Every big truck you see on the highway has a diesel engine and at least one turbocharger. It is common for them to run more than one million kilometres with no problems with the turbo, so don’t fret about yours as long as you follow VW’s suggested maintenance schedule and procedures.
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