Chingy,
150,000 miles almost almost quarter million kilometer and that is a lot of mileage.For old engines Castrol recommended GP Multigrade a 20w/50 oil. I wonder if it is still available now a days.
If you are not a very cold climate SAE 20w/40 viscometrics should be a good bet, for fairly cold climate suggest 15w/40. Castrol GTX and its variants like Magnatec should a good choice.
Hussam Adeni