Should you let a turbo engine idle before switching it off?
After normal driving, no. After sustained high load — a track session, a fast motorway run, a mountain climb — yes: give the turbo a short, easy period before switching off. The reason is what happens to the oil inside the hot bearing housing once the engine stops.
What happens at shutdown
Under load, the turbine side of a turbocharger runs extremely hot, and oil flowing through the bearing housing carries that heat away. When the engine stops, oil flow stops too, but the housing keeps soaking heat from the turbine. Oil trapped in the bearing area can overheat and oxidise into hard carbon deposits (coking), which restrict oil passages and wear bearings over time.
Why modern engines are more forgiving
Most modern turbos have water-cooled bearing housings; after shutdown, coolant circulates by convection (thermosyphon) and many engines run an electric coolant pump and the radiator fan after the engine is off. Modern synthetic oils also resist coking far better. That is why routine idling before shutdown is not needed in normal use.
When it still matters
After sustained full-load use, drive the last minute or two gently, or idle for around 30–60 seconds before switching off. Long idling is pointless and adds fuel dilution. Do not switch off and immediately open the bonnet to “cool it” — let the after-run systems work. Also: do not load a turbo engine hard until the oil, not just the coolant, is warm.
See alsoEngine Diagnostics & Repair →Minor & Major Servicing →