The manual for my 2000 F23A1 states to use 5w-30 or 10w-30.

I had run 5w-50 synthetic--I switched to 5w-30 synthetic for the last year and I have seen no difference, so go figure. The best gas mileage I ever had was on 5w-50, so I may switch back because its easier to find 5w-50 then 5w-30 Syntec in my area.