I have a 95 merc 5.0LX alpha 1-engine # OF588144. Last spring i replaced the water impeller because of overheating. Then i noticed a knocking not a tap in engine and oil pressure dropped to between 5-10 psi light on dash came on at idle when hot. I messed with it the next day again and again and nothing. It will only do it on the water when hot at idle. When engine is up to 1000rpm it will go away, not sure. Thought it may be a bearing somewhere but i change oil again, now im running 20/50 and 1 bottle of lucas. Got 20psi now when hot but still slight knock. Ran it all summer and never changed. I winterized it and just took it out for 1st time last week, now my water temp doesnt work while running the boat. Ran it about 20mins and still no temp. I put a mech temp gauge last year and when you shut down, after few seconds temp will go up to 160. Start up and it will go down to 100 or less. My elect gauge on dash will do the same. 1st i took out termostat and it was open, let it cool down and it will close. Then i started it, put my hand on thermo housing. It will get hot then cooled, so that seems to be working. Ran it for another 20mins and nothing changed. Temp will go up to 160 when not running. I felt the oil pan and it was very hot. Not realy sure if the oil should be that hot. Maybe thats why i lost oil psi last year, not sure. I check the front water pump and the pulley is tight. Thanks, hope someone can help.
