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Thread: 496 Issues

  1. #1
    Wizard29
    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...

  2. #2
    DMOORE
    Most likely you poped a head gasket. It doesn't take much on a 496 to do it. In the future, if you get a high temp alarm, STOP immediately. Shut the motor down and do a check of the water intake. You would be suprised how little grass or weeds it takes to cut off water flow. BTW it only takes a short time fot the rubber impeller to disintegrate from no flow.
    Darrell.

  3. #3
    Wizard29
    I hope to hell it is only a head gasket. Anything more than that will likely be a huge pain in the ass (not that this isn't already). This engine does have the Pro-Charger too, so a head gasket is likely.
    Would a head gasket cause oil to come out the exhaust though? I'm not too sure about that...

  4. #4
    DMOORE
    Would a head gasket cause oil to come out the exhaust though? I'm not too sure about that...
    If it lifted it good, it sure can.
    Darrell.

  5. #5
    finsfan4life
    Sounds like u need to check the validity of ur friends certification...are u sure u want him to touch it again...Sorry for the brutal honesty...

  6. #6
    Wizard29
    Sounds like u need to check the validity of ur friends certification...are u sure u want him to touch it again...Sorry for the brutal honesty...
    No offense taken. That thought had crossed my mind, to tell you the truth.
    He is Merc certified and works at a shop in Boulder that does a lot of performance work. Apparently a lot of Hallet guys from Mead bring their boats to that shop. The name of the shop escapes me at this moment, but they just sent him on a trip to New Zealand to participate as a mechanic in some boat races there. One would think they wouldn't spend the money to send him that far if he wasn't any good.
    He has also done a lot of work on people's boats at Cottonwood Cove and brought much credit to himself there. I've not heard of anybody who has been dissatisfied with his work.
    So, we'll have to see how this goes. Hopefully it is just a blown head gasket and I can be done with this soon. I'm just concerned about the oil coming out of the exhaust on the left side. Never seemed to me that could be caused by a head gasket...

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