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The oil bakes on the bearing journals and slightly damages the surfaces.Then the shaft picks up on the uneven spots which increases wear over time.
After that you will eventually get excess run out on the shaft and contact between compressor or turbine wheels on the housing,then it gets messy.
I don't have a turbo timer, but do generally try to let the motor idle for a little while before shutting off if it has been working hard. However there has been the odd occasion where without thinking I've just switched off, only to immediately think 'Bugger, shouldn't have done that'. On these occasions I have then immediately re-started the motor & let it idle for a while. Is it better to do this once switched off or not?
Cuppa
Yeah it would be cuppa,the shaft and bearings would have a chance to cool down below oil burning temp.But shutting down hot a few times won't cause too many issues it's only when it happens regularly
would it be worth having a temp gauge on the turbo itself?
I used to wait until the egt registered 150deg before I turned off the 3ltr off. It used to idle for about 2 min.
Now I have a turbo timer in my TD42 and set it for 2 min as majority of my driving is at highway speeds and not hooning.
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The oil in combination with the extremely hot turbo causes the oil to break down which becomes carbon that sticks to the walls of the oil pipes, gradually causing it to clog up up over time. Easiest way to cool the turbo is to back off your right foot a few km's before arriving at your destination.
Its not so much the EGT's or the water temp to cool down, its the oil temp cooling down that's what's required.
I have had my tubo on my GQ 4.2 since 1991 ish and also have an oil cooler and a timer and the timer always runs at least 1 min but 3 or 5 if towing or hyway driving.
Its still working so maybe a timer and oil cooler are worthwhile.
Cheers
Chimo