What is the heaviest oil I can use in a Ford Explorer SOHC 4 liter engine? Beleive 5w-30 is recomended. I have a timing change rattle at warm idle i want to reduce the noise. I do not want it to slap around so much (might slip time)and thought that thicker oil might help. Fixing is not an option right now. Dealer wanted about $3,000 to fix front and rear timing chain issues. Opinions?