Let's start by saying that the 3.0 XC70 is a BEAST. It's a very special car and there's nothing even close to it being made nowadays. It is a very reliable car, pretty much it's the last of it's kind.

The "Volvo Short Inline 6" (more specifically in your case the B6304T4) is a very special engine that was used on top Volvo models and on Land Rovers. Although this engine is not the longest lasting of the Volvo lineup, they typically last over 200k given that you maintain it properly.

The only thing I'd really worry about is not putting too much strain on the automatic and keeping the transmission oil clean (Service intervals: 8 speed automatic - every 60k miles, 6 speed automatic - every 45k miles, 6 speed dual clutch - every 30k miles)

NOTE: A strong whistle under the hood on that engine just indicates you need to replace the oil separator. If these are your only symptoms maybe you do not need a whole new turbo unit.

@Kerem - thanks for letting me know of this question 😀, I hope I have helped.

Automatic transmission on these cars are weak their point and have some issues. Regarding the turbo question, it only depends on how the car was taken care of. With that being said, I would consider Toyota or Honda before choosing Volvo. 

Those cars are actually pretty good. The AISIN transmission's problems were mostly ironed out and its a decent wagon. I doubt you need to change the turbo without it going bad but I'm not an expert in that regards. I personally would have gotten a naturally aspirated variant but those engines are also alright from what I know, but still its a European luxury car and you will eventually pay premium for repairs and maintenance.

Honestly, I've always liked Volvo. There cars are of good quality, and used ones are farely reliable if you consider they are Chinese owners, European, and a not so popular luxury car brand. Realize all Euro brands will eventually become "endless money pits."

If it ain't broke don't fix it. Preventive maintenance is good and all that, but the second you start working bout things that ain't broke just yet you gonna get a headache thinking about all the things that could be wrong. Get it check out by an honest mechanic if you don't know what you are looking for/at. If they say it's good then you all good dude.

We had a 2011 XC70 Polestar edition. Was a really good car. bought it used and had it for 3 years 85k miles to 130k miles. Only issues was that one of the coil packs decided to fry itself. So we changed them all out and spark plugs while we were at it. No issues with the turbo while we owned it.