This September i changed the oil in my Ford Capri with mineral 20w50 ( Shell HX3 ), Instead of the 10w40 semi synthetic stuff i had been running before that ( Mobil 2000 ) , it really is noticeable that now the engine is running on the oil grade that is specified from the factory.... everything is better but how often should i change it? i've been advised to change it every 3k miles / 5k km or 1 year, whichever comes first , i only drive about 2000 Km / year so is it unnecessary to change it every year? i do about 50% city and 50% motorway driving with mostly long drives where the engine gets up to temp but some short ones where the engine does not , am i also safe changing the filter every 6k miles or 10k km? i live in an island so it's always very humid ( +70% ), winters are mild but summers are very hot and temps can get up to 100 F ( 40c ).