There's a lot more to engine oils than people realise. Some oils contain extra additives and detergents to keep the engine running smoother and cleaner and protect certain parts etc. I tend to stick to main brands of oil such as shell, castrol etc for normal changes, and reserve the posh stuff for high performance cars or cars still under main dealer warranty. You can pick up some really cheap oil from places like ASDA but I tend to reserve this for flushes etc and dont run on it long term. (although nowadays ASDA own brand could well be Shell or Castrol etc)
