I beleive in Castrol GTX Magnatec 10W-40, there is some extra advantages
Every time you start your car it takes most oils 10 minutes to work effectively, because the oil cannot protect properly until it reaches a critical temperature. Castrol GTX Magnatec 10W-40 for Modern Engines is different as it gets to work straight away by virtue of a unique synthetic ester that clings to the engine like a magnet - this "Unique Molecular Attraction" provides up to 4 times more protection than a conventional oil during the critical start and warm up period
Offers 4 times better wear protection than ordinary oils from start up
Provides critical engine protection during start and warm-up periods
Oil clings to the engines surface like a magnet providing constant protection even when the engine is switched off