This man knows what he's talking about...

Here's a tidbit from cummins website:

Engine Operating Temperature (Coolant and Lube Oil)
Low coolant temperatures indicate an engine that is too cold for efficient combustion. Fuel liquefies on the cold cylinder walls and fails to burn. Of course, excess heat causes engine failure.
Lube oil below the ideal temperature is more viscous and harder to pump. Oil above the ideal temperature is too thin to lubricate properly. Either way, the engine suffers.
Coolant and lube oil operating temperatures can contribute greatly to fuel efficiency. Typical cooling system operating temperatures are above 180° F. A 0.4% fuel economy loss is associated with every 30° decrease in temperature.

 

Aluminum expands twice as much as iron does, no matter what you do.

That's why pistons have a decent clearance in the bore. Room to grow.

That's also why overheated engines scuff the pistons in the cylinder, they've expanded too much.

 

I always let the engine idle while doing paperwork then shut down. On my personal truck, I usually idle through the neighborhood on the way to the house and it's good to go. Either way, it should idle a few minutes as stated above.

 

" Lack of lubrication damage can also occur if the oil supply to the turbo is shut off before the turbo has had time to slow down. It is normally recommended that an engine be allowed to for a few minutes before shutting off the engine. This lets the turbo slow down as well as cool before shutting off the oil supply." http://www.dieselpage.com/art0898tu.htm

"The most common failure of automotive turbos is due to hot shutdown. This occurs when the vehicle has been running at a constant speed for a period of time and the vehicle is shut off before the turbo has had time to slow down. A turbo can spin at speeds exceeding 100,000 rpm, the faster the vehicle goes or the harder it works, the faster the turbo will spin. If a vehicle is shutoff suddenly the turbo will continue to spin without oil. Each time this occurs, the life of the turbo is shortened because of wear occurring from no lubrication. Eventually there will be enough wear to allow one of the wheels on the turbo to contact its housing. This causes the wheel to be out of balance. This causes even more contact and the turbo is usually destroyed. Allowing the vehicle to idle for a few minutes after its been running hard or allowing the exhaust temperature to cool to below 500 degrees will greatly reduce the risk of premature turbo failure." http://www.dieselpage.com/art1110fd.htm

kc0iv

 

I agree that the reason to idle the engine for a few minutes before shutting down is specifically for the turbo to cool down and is important to do. Also I'm all about letting a engine warm up. I usually start it up and let it idle for about 5 minutes and then kick the idle up to about 800-900 rpm for another 5 minutes and then hit the road taking it easy for the first mile or two. In cold weather I let it idle a couple extra minutes on the initial start up. I see drivers start their truck cold and not even 20 seconds goes by and they're bangin' through the gears goin' down the road. Nothing may go wrong for thousands and thousands of miles but eventually it will take a toll on the engine. I installed a remote start on duramax pick up so I could let it warm up a little bit and idle for a minute or two when shutting it down.