Turbocharger

A turbine wheel in the exhaust and a compressor wheel in the intake share one shaft spinning at very high speed. The extra air allows more fuel to be burnt, so a smaller engine can make the power of a bigger one. Turbos rely on engine oil for lubrication and cooling. Many diesels use variable geometry turbos with movable vanes; petrol turbos usually use a wastegate.

Turbos are common on modern petrol and diesel engines because they let smaller engines deliver more power with lower consumption. Turbos spin very fast, often well above 100,000 revolutions per minute, and run extremely hot on the exhaust side. Common causes of turbo failure are oil starvation, contaminated oil and foreign objects entering the compressor or turbine. Blue smoke, whistling and loss of power are typical signs of a worn turbo.

Boost is controlled by the wastegate or vanes. An intercooler cools the compressed air before it enters the engine. Exhaust gas spins a turbine; a shaft connects it to a compressor that pushes air into the intake. An intercooler cools the compressed air before it enters the engine.

Oil starvation, dirty oil and boost leaks are the main enemies. Signs of trouble are whistling or siren noises, loss of power, blue smoke and boost codes such as P0299. Turbos depend on clean oil. Avoid hard driving with a cold engine and let a hot engine idle briefly after hard driving if the manual recommends it.