Turbo engines

[fairy!]

Is it true that if you have a car with a turbo engine, you should leave it running in idle for a minute or two before switching the engine off at the end of a journey??

[Loosehead]

generally you can hear something after you have turned it off so I assume that it's automatic so I'd be surprised if you have to worry about it yourself.

[ianess]

As an ex bus driver, many years ago it was a recommendation to let a turbocharged diesel engine idle for about a minute before switching off.  Don't know if it still applies but I think it was something to do with allowing pressurised oil and fuel to drop back to minimum levels.  Does that make sense?

[jake-the-peg]

It's a good idea yes.

Turbochargers spin very very fast and when you turn off the engine the oil stops being pumped around them which can cause premature bearing wear.

Less of an issue if your normal commute involves a 10 minute poodle around the backstreets before you get to your destination but a real brute if you zoom down the motorway and stop and switch off at a service station.

Turbos also tend to last a lot longer if they're given regular oil changes and some people say talking to them helps too 

[Clanad]

ianess isn't too far off... A turbocharger works because exhaust gases are routed through one side (impeller), which turns the compressor on the other side.  In between these two sides as well as else where in the device, are bearings that are lubricated with engine oil.  While in cruise speeds the turbo is spinning at very high speeds, some turn in excess of  125,000 RPM's.  The compressor side of the device is also quite hot due to the compression (clever, no?) of the air.  So... if you come to a quick stop after fairly high speeds, the trubo continues to spin.  If you shut the engine off at this point, there is no longer any oil pressure to the bearings and the device still is heat soaked.  Letting the engine idle for just a few minutes will let the compressor spin down and the wear will not be as great...

[fairy!]

Thankyou very much everyone! :-)