First off..jet boat with BBC. It's a 70'S LS7 motor. Stored inside my heated garage all winter at 50*. Two times this winter I went out into the garage and just fired it for 15 seconds..do that every winter..no water hook-up. Went out this morning and changed the oil. The oil on the dip stick appeared to be fine prior to changing. When I pulled the filter I thought it look a little strange. Put fresh oil in with new filter and ran it on the hose..milk shake. Thought maybe I ran too much pressure on the hose etc..changed the oil and filter again and went down to the lake and started the boat on the trailer, in the water...started to milk shake and came home..the big question is where should I start..could it just still be moisture in the block and not run long and hot enough...pull the manifold, compression test, leak down test or what..thanks for the help..Not sure if I should have posted here or in the jet boat section..