I have an '03 Merc 496HO in my Magic. Has a Pro-Charger at 3.5 PSI, but is otherwise stock. Here's the story:
Prior to this Memorial Day weekend, I had a friend of mine (certified Merc tech) change my water impeller as a preventative measure. The one that came out had been in for about two years and looked perfect. Boat ran fine on Saturday and Sunday with the new one.
Curuising along in some rough water on Monday at about 3200 RPM and I get an alarm. I look at the temp gauge and it shows 1/2 (there are no numbers on it). It usually runs at 1/4 or very slightly more. I let my friend know what is going on and limp it back to the ramp. By the time I get to the ramp and on the trailer, the temperature is 3/4. Never been that hot before.
Dig into it on Monday night and find the new impeller completely shredded. Not sure what caused that, but we put a new one in, got all the pieces out of the system, and took it back down to the ramp to fire it and make sure water is flowing.
I fire it up on the ramp (in the dark). Water is pumping out the back, but after bringing it up to about 2000 and back down, I notice a weird vibration and hear a knocking sound. A bunch of steam was coming out the rear and a mixture of oil and water was coming out of the driver's side pipe. I shut it down, wait a minute and try to start it again. It begins to turn over, but stops as if something had jammed it. Great.
My friend thinks it is probably a blown head gasket or a cracked head and it won't turn over because one cylinder is hydraulically locked due to water in it. Makes sense. The engine got hotter than it has ever been, and could have damaged something. He'll be tearing it apart to see what he finds.
Are there any other thoughts as to what the problem may be?
If it is a head gasket, no big deal. But, if it is a head, then what? I can probably find some stock replacement heads for a decent price, but what about some aftermarket ones since we're here anyway? Could I buy a set of Dart Pro 1 aluminum heads and put those on?
What a shitty weekend. Any suggestions on which way to go with this situation are appreciated...