496 Issues

[Wizard29]

I posted this in the Sandbar, but thought here may be more appropriate...
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...

[Just foreplay]

Don't feel alone, I'm going through that also...
Your guess sounds right, blown head gasket and hydraulically locked.
The other alternative is machine the heads and use a "over sized" gasket to bring compression ratios back to normal/ stock range.
If you change heads, you will need to reprogram/ calibrate the PCM...
I had to mill of .006 to get a straight/ true head. I used Felpro gaskets because of availability.
Good luck

[twowheeledfish]

First thing to address here is the possible misstep when installing the new water pump impeller. If you don't grease the hell out of it during assembly, it will run dry upon initial start-up until the system primes itself... enough to damage the new impeller. The grease allows it to spin without friction until the cooling system gets wet.

[Wizard29]

I hope it is just a blown gasket. That would be the easiest and least expensive solution.
The most concerning thing is the oil coming out of the exhaust. I wasn't aware a blown gasket would cause that.
The impeller was soaped down pretty well at installation. The weird thing is it ran very well for two days and then decided to grenade...

[Just foreplay]

I hope it is just a blown gasket. That would be the easiest and least expensive solution.
The most concerning thing is the oil coming out of the exhaust. I wasn't aware a blown gasket would cause that.
The impeller was soaped down pretty well at installation. The weird thing is it ran very well for two days and then decided to grenade...
Just pull the head and that will be the tell all..
When I pulled mine, I noticed some factory plaws in the heads. Probably would not have been a big deal until I put a whipple on her...The added pressure, was all it took..Only had 10 hrs since whipple install. Only 38hrs total on new motor.

[twowheeledfish]

The impeller was soaped down pretty well at installation. The weird thing is it ran very well for two days and then decided to grenade...
That is odd, man. Is it possible that you pumped sand or pebbles into the system?

[Wizard29]

Very, very, very remotely possible. I don't beach it and never have it anywhere near sand or gravel. I reconstructed the impeller after I found all of the pieces, and it looks like there may have been something in there, but you just can't tell.
After I get it all back together, this thing is getting a sea strainer.

[twowheeledfish]

Good call, bro!

[Wizard29]

The heads were pulled off today. A combination of oil and water was found in the rear cylinder (#7), which was the cause of the locking up. Other than that, all looks good. Pistons are clean, no hung rings, cylinder sidewalls look good. The gasket shows no apparent signs of failure, although you can't always tell just by looking.
The heads are going out for magnafluxing and we'll see what the results are soon.
A combination of oil and water (not antifreeze from the closed cooling system, it's fresh water) in cylinder #7. What can cause that?

[DMOORE]

Fresh water in the #7, is really wierd. Since it is a closed water system I would be looking into some sort of leak in the exhaust system. Is there a possibility water was somehow forced back through the exhaust? It might be worth having the exhaust pressure checked. It's just really strange.
Darrell.

[Wizard29]

It is quite strange. My friend is going to pressure test the exhaust too while he has it off.
All I can figure is either my friend is mistaken and what's in #7 is actually a combination of oil and antifreeze (not fresh water) or this is a comedy of errors involving a blown head gasket or a cracked head combined with an exhaust feeding water back.
I'm crossing my fingers for a blown head gasket. If the exhaust happens to be bad as well, then that's okay. I'm thinking I want to put some EMI Thunder headers on anyway while this thing is apart...