I have a 3 year old 4 cyl Toyota Camry with 5500 miles on it, Ive been using 0w/20 Mobil 1 & Wix filters at 6 month intervals since new. Lately I've read of possible sludge problems doing this. Is this a problem or am I OK, this is my wifes car. Wondering if I'd be better off using cheaper oil at 3 month intervals. I'm 73 years old and like the 6 month deal if its OK.