Took me a min to answer because I had to go look at the Royal Purple synthetic blend bottle I had to make sure I answered your inquiry right. 10W30 viscosity. The prob with full synth is that most cars back then didn't start out with it. Since yours is a high mileage car (my '91 has 88k) you never know what the previous owners were using, and you really want to stick to whatever the car is used to.
I mean it's not dyer, you can switch but it's best to stick to one type. RP has worked great for me since five years ago.