Gonna step it up to a -10. I dont see the need for any thing larger since the oil filter adaptor is 1/2" and the pick up tube is 3/8". How would using larger hose on the cooler improve any flow when the pick up is smaller? Can only get so much oil thru that 3/8" pick up. _10 is .530" id. Should be more than enough. I would like to hear from anyone that had a failure using anything smaller than -12 hose on their cooler system.