I just purchased a 1997 19 century center console, Has 97 Yamaha 130 Saltwater series. I have a knock under 1300 rpm, Sounds like to me it is a rod knock yet coming from under flywheel or so it sounds. I also have a overheat alarm above 3/4 throttle. Now I just pulled lower unit off to check impeller, Looks ok ( I will order and replace anyway as it is a year old and is time) T-stats also look like they have been replaced due to new t-stat covers. The cooling part I understand and will fix that issue, Weather i got to pull heads and clean passages. but the knocking worry's me, I pulled the lower off and started motor for 10 sec found I can not hear the noise at all, of course motor is a little louder without lower. So sounds like its a lower unit problem? P.S. Compression check is great.