1985 50HP force cooling question

[steve242002]

Hey guys, im bran new to this site but I love the forums that I have found so far. Anyway, i have a 85 50hp force, I dropped the lower unit to inspect the impeller and it looks great, there is plenty of the sputter water coming out of the exhaust but there is nothing at the thermostat, in front or behind. I took it out today for the first time this year and after about ten minutes the overtemp alarm went off. I took the exhaust manifold/cooling cover off the side of the block to expose the pistons and all the ports looks great, little bit of salt residue but no blockage that I can see. Last year after I used it last in the sound I flushed the water lines with the hose bib and it worked great, never before have I had this problem. It worked great all year last year. Could something have broken during the winter? Is there anyway I can test the system? Any advise would be great. Thanks everyone.