Don't take my word for it- - - - -do a test. Take a metal 1-cup measure and drill a 1/8" hole in the bottom. Then use a stopwatch and time how long it takes cold, then hot (200 degree) 5W-30 oil to drain out. You'll probably be surprised to find that the oil doesn't "thicken up" as it gets hot.
I run 15W-40 in everything I own - - - -lawn mowers, motorcycles, Diesel farm tractors, cars, and trucks. The reason I recommend 30 weight for the flush is that it's going to be diluted with a couple of gallons of Diesel fuel. If you have a few quarts of Valvoline 50 weight racing oil handy, you could use that for the flush job (not for everyday operation).
Jerry
