Are there any precautions I should follow with regards to turbochargers on stop-start engines?

As I am contemplating buying a car with Renault's TCe 90 engine I have read with interest your recent comments on overheating turbos and would appreciate your advice on some points. Does carbonising build up or is it sudden death? Does engine temperature gauge bear any relation to turbo temperature? If I have used a turbo on a motorway, would a further ten minutes on suburban roads be sufficient to cool it enough so that further idling is not necessary? What precautions will be required with stop/start engines?
A petrol turbo is watercooled as well as cooled by engine oil running through the turbo bearings. Carbon eventually builds up in the oil feed pipe to the turbo if the engine is regularly switched off when it is too hot, resulting in the oil in the turbo feed pipe and bearing carbonising. A proper stop start system does not stop the engine when the turbo is too hot and when the turbo is watercooled the engine temp sensor will detect excess heat because it's the same coolant. Yes, the run from the motorway to a final destination at reduced and varied revs is usually enough to cool down the turbo.
Answered by Honest John on

Ask Honest John