Cars used mostly for short journeys will benefit a lot more from more regular oil changes than they will from fancy high spec oils that only benefit high performance engines.
The book says 10w40 semi synth changed every 12000 miles but it's common sense that a town car used for short journeys will stress its oil harder than one that does longer runs. I would prefer to use a cheap correct spec and change it more often as a dirty oil is bad for the engine regardless how fancy the stuff was when new.
Dave pretty much says it all here. Cheap, correct spec oil, changed regularly with a new oil filter every time does just fine for our wee engines.
We have 6 cars in the family 5 of which I look after They cover the spectrum really from our wee 1.2 Panda and daughter in law's 1.4 idsi Jazz, older boy's 1.4 8 valve Punto and younger boy's Astra 1.6 with their relatively simple old normally aspirated port injected petrol engines to our older boy's Kia Rio with it's turbo diesel (driven mostly by his wife) and my Seat Ibiza 1.0 tsi eco with it's highly stressed direct injection turbo petrol engine.
The older cars all trundle along very happily on cheap, but correctly spec'd, oils bought from my local factor (TradeTEC brand) which get changed yearly (under 10.000 miles) except the Astra which is a business car covering about 15/17.000 miles yearly so it gets changed every 6 months (still the TradeTEC though) - always with new filters. The Kia and Ibiza worry me more because of their turbos, which are well known to stress oil. Both are direct injection so have highly stressed fuel pumps and, because they don't inject fuel into their ports are liable to suffer carbon fouling of their inlet systems. I don't have much control over the Kia as it's under this 7 year warranty so gets done by the Kia garage so that if there is a warranty claim things should, hopefully, go smoothly? - I must ask them what oil they are using, probably won't get an informative reply though? - The Ibiza, which is just out of it's warranty, will be getting the best that TPS can supply. (Trade Parts Specialists being my preferred dedicated VAG parts supplier). The Ibiza, being a small capacity, turbo, direct injection petrol engine is potentially the most fragile and will be "spoiled" to a much greater degree than any of the others!
It's worth being aware that many engines now have screen type oil filters which often are not mentioned at all as service items. VVT engines - My boy's Astra, The Punto (which has a Euro 5 engine), My Ibiza just for starters - have screens on the VVT solenoid valves. I don't have experience with the Hydraulic valve system on the Fiat engines but I know there is a screening filter in the feed to the actuators which requires occasional replacement. Of course there is a screen filter on the main pickup in all engine sumps. Frequent oil changes with a fresh filter every time goes a long way to reducing the chances of these filters and smaller oilways from getting blocked up.
