I notice your car is a diesel - therefore, it’s likely that your car’s diesel particulate filter (DPF) was performing an active regeneration to burn off accumulated soot deposits in the DPF. The very high temperatures reached during the DPF regeneration process means the engine cooling fan will be activated to help cool things cool.
When I owned my mk6 Golf GTD (the last diesel car I owned), other tell tale signs of an active DPF regeneration (noticeable in slow moving stop-go traffic conditions) were;
- a ‘hot’ burning smell
- engine rpms at idling speed higher than they usually are
- the gear change indicator (manual car) indicating the need to change down to the next lowest gear to keep the engine rpm’s up.
- an increase in fuel consumption, as additional fuel is used to aid the regeneration process and burn off the accumulated soot deposits
- in cars with stop start (my GTD didn’t have this), deactivation of the stop start function
If most of your journeys are short, lower speed trips where the engine may not always get up to optimum operating temperature, you may notice the DPF regeneration process happens fairly frequently, as soot accumulation in the DPF will be greater than it is for a car travelling predominantly regular, longer journeys on a fully warmed up engine. On longer, high speed journeys, the DPF regeneration process is passive and you’ll probably not be aware it’s happening.
Also, if you are aware your car is midway through performing a DPF when you reach your destination, I would suggest you extend your journey by a few miles so that it can complete the process and fully burn off accumulated soot deposits before you switch off your engine.
EDIT; when the gasoline particulate filter (GPF) in petrol engines cars is going through a regeneration, I think there’s a message displayed under the ‘vehicle settings’ telling the driver to keep the engine running. There may be a similar message with diesel cars - i.e. to keep the engine running until the regeneration process of a complete - so next time your DPF is regenerating, it’s be worth checking your vehicle settings via the infotainment screen.
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