I am running AMSOIL 20W50 in my VW jetta. The engine likes it but I feel the oil is too thick. Since I race Solo events each run takes about less than 5 min. Should I be using 10W40? Are there any other oil that is better than AMS at lower price? I can get Mobile 1 for about $6 a liter AMS costs me $9.2 Castrol is about $6 too but I heard both Mobile and castrol are not true synthetic oils.