Hello everyone, I got Volvo 850 2.0 turbo (155kw) italian T5, and I am planning to change the oil, it has ~450k km on odometer, and as far as I know previous owner used 10W40 semi synthetic oil for quite some time. I read on several forums that it would be better to use fully synthetic oil in turbo engine, so I would like to switch to synthetic, and want to know if it's worth for such pretty high mileage car. It doesn't seem to leak oil now, maybe just a little from oil cooler lines, which I am planning to replace. I replaced all 4 camshaft seals a month ago, when I was replacing timing belt, and turbo drain tube seal, those were leaking. So the only old seals remaining in this engine is RMS one and front crankshaft seal. I live in Lithuania, temperature at summer rises up to around 30 C sometimes and drops to -25 C or little more at winter. So I guess 5w40 oil would be a good choice if I can switch to synthetic, or I should stay with 10W40 oil? What about Total quartz energy 5w40 or Total quartz 5w40 or shell helix ultra 5w40? Castrol gtx 10w40?