What speed you drive at or what RPMs you are working in have utterly no bearing on reliability or longevity of the engine.
It is far far worse, to be doing very short journeys and pretending to be a 90 year old Sunday driver who never breaks 1500rpm.
Allow me to explain why.
If an engine is never worked hard, the engine oil never becomes hot enough to evaporate all the fuel and water that tends to accumulate in it. Secondly, the exhaust system, which has a pretty pants job in life, never gets hot either. 30 years ago, that didn't matter much because the car generally rusted to death about the same time as the mild steel exhaust system did. In a modern car, the exhaust system is home to catalysts and engine sensors. If these don't get hot and seared by hot exhaust gases, they coke up with soot and skank and basically begin to refuse to work.
I don't mind if you have a 3 cylinder 1 litre petrol, a V8 twin turbo diesel, or a V12 Ferrari, you must never cane an engine until the coolant and oil is up to temperature- as in the needle is where it normally lives. This means driving along steadily but keeping the revs low until the car is warmed.
Likewise, particularly with turbocharged engines, please don't drive home at 7000rpm, park on the drive and kill the car in an instant. Certainly never kill the engine from high RPMs (oil starvation of the turbo which is of course spinning at about 100,000 rpm), and for turbocharged engines it is best to let the car idle for a minute before turning it off, so the heat in that turbocharger is at least dissipated a bit. Not such issue these days with modern oils but there we go. Alternatively do what I do and cruise home the last few miles at low RPM so there isn't a huge amount of heat about anyway.
The one thing you need to do is get the thing serviced on the dot as recommended by the manufacturer. Oil and filter, if nothing else, just do this. Coolant out when the book says. It costs sod all in reality and they will check the brakes and other essentials at the same time.
People who are experiencing failures either have inherent manufacturing faults, excessive wear in various components (probably due to acting contrary to the above) or are causing stress in some way, the classic is by over-revving when people change down too soon and fling the engine above the red line- this is ill advised.
Modern cars and materials science is such that this is old hat today. Volvo like most makers have already built a car before yours and tested it to death in some terrible environment.
Go on an American car forum and see the simply astronomical mileages these guys attain. The fact their cars would never pass our MOT is secondary but I can't emphasise enough that generally today your average mechanic is not getting piston ring failures or head gaskets or big ends going when 30-40 years ago they were commonplace.
In fact I would go so far today to suggest that what kills most high mileage cars today is uneconomic repairs or corrosion (although even that is much reduced today).
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