well use your own discretion obviously, when your turbo's glowing red after a hard drive in negative degree whether, you're going to want to wait even longer. but corner store drives don't really need such a long cooldown period cuz short drives don't really heat up the turbo unless you plan on boosting hard to the store and back.
by letting it idle you're letting the oil in the turbo run its course and cool it down, if you've been ripping your turbo and you shut your car off that turbo will be going from red hot to icey cold in a really short period of time which could potentially damage your turbocharger

 

i have heard of horror stories where turbo and mainfolds literally blown and warped. I mean its always good to cool it down no matter what.

Basics are, turbo uses same lube that engine does, in fact it comes from the same source. So thats were change oil and such come into play in keeping turbocharger healthy

Apart from the temperature matter described above, oil will not be drained back into the storage like thing at the bottom of the engine, therefore it will be stuck inside the turbo. I don't remember the process exactly but it will "gel" up and destroy the turbo.

By the way, despite popular beliefs turbo starts working at about 2000 RPMs not 3000, i see a lot of people thinking it kicks in at about 3000. so i imagine it can be kinda hard to keep RPMs that low through out entire trip. so cool down is always needed. if you drove slow and not far, like down the street to the next house 20 sec is okay, as there isn't that much oil build up.

Just saying for myself but i know it looks wired when you stop and just sit there with car on, i get looks of like WTF???? so pull out your phone and pretend to do something lol dial a random number call and say hi BAM!!!!

 

mistake

 

I recomand the use of 100% synthetic motor oil and a resonable idle time to cooldown.
The shyntetic molecules maintain the vicosity under extreme temperatures high or low.
I only use synthetic oil since 1980 two milion kilometers and never had an oil related engine failier. Is good enough for all internal combustion engines includig lownmoars.
Mike

 

this noise you are hearing is the secondary air pump coming for emissions.... when you start your car when its cold out its starts in warm up mode, which makes the car run alot richer (more fuel).... this pump just helps more air get into the intake to reduce emissions..... took mine off on my old gti....

 

I personally don't recommend synthetic. Conversional is much better in a long run.
In the winter you can use less viscose oil.

Synthetic is better all around but its expensive. And i find people don't change it as often.
I spoke to a few mechanics and they all recommend just to use regular oil and change it more often, you will end up with a cleaner engine. I change my oil every 4000 - 5000 k while synthetic has higher life span, its still better to keep cleaner oil. It comes out to same price, but you end up changing your oil three times rather then one. If you can afford to do the same thing about 4000 -5000 with synthetic, go for it, but for broke people like me, conversional is much better.

And it help to reduce sludge as it more often flushed ( if you choose to)

 

I don't think changing oil longer than 5000 k is recommended for any type of oil. Sure synthetic may have greater viscosity, but I agree with GeneKam, more frequent oil changes preserve your motor, and if you can afford to change your oil every 4-5000k by all means go for it.