Hello,
been putting Castrol 10w-40 Semi-Synthetic oil in my 2008 TDI 1.9 105 since new. It's be fine no probs, even though the car has 147,000 K. Being driving it warmer countries, Italy. Been back in the UK for 6 months now. Is this oil OK for my car or shall i shift to Castrol 5w-30 now that...