I use 10W-30 in the winter months (Oct - April) and then switch to 15W-40 in the summer (May - Sept). I have been using the Royal Purple non racing grade of
Synthetic for about 3 years now. Works great although the 9 quarts does not get much mileage on it. I am using the K&N
oil filter. It appears to be an excellent filter and I like the nut on the end of the filter for easy removal. I do two
oil changes per year with filter. I put about 3000 miles on the car, most of it with 15W-40 in the sump.