How hard does the turbo work under normal driving conditions?

You quite rightly advocate running a turbocharged engine at idle for a minute or so after a vigorous run in order for the turbo to 'cool off', and my last car (Toyota Yaris Diesel - bought on your recommendation and a splendid purchase) displayed a panel giving a message to that effect. I now have a manual Rover 75 Diesel 131PS and this is an equally splendid car. But how much does the turbo get involved in normal driving use?

The reason I ask is that for practically all driving conditions 2000 to 2500 revs is all that is needed and the engine does not seem to even break sweat under these circumstances. Even through the intermediate gears it isn't necessary to exceed 3000 revs to achieve rapid progress (2250 revs giving 70mph in top), so does the turbo even get employed under such conditions? Also, there seems to have been heated discussions about the effect of the weight of unnecessary items in the boot on fuel economy. Any views?

Asked on 23 March 2013 by SG, via email

Answered by Honest John
The turbo will be spinning all the time, but only actually boosting significantly from around 1500rpm. The reason for idling is to keep engine oil flowing through the bearings, lubricating and cooling them while the turbo spools down from maximum revs of around 100,000rpm. Normally low revs driving between the motorway and your home will do the same job but, if you live up a long hill, or if you tow anything, it will be necessary to idle the turbo before switching off.
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