please help, head gasket?

[alaskanassassin]

I had a bad start to my boating season. My 2004 mercury 200hp carbed v6 blew an impeller and no overheat alarm. I heated it up enough to melt the insulation on a wire touching one of the heads. I replaced the impeller and housing and ran it. It runs great until it warms up, then the idle slowly drops until it quits. I restarted it and it runs fine for a minute but only with my idle lever up a ways, then rpms drop, etc. When I pulled it back on the trailer and dropped the motor down, lots of oil (mix, not gear oil) came out the center of the prop. I pulled each spark plug and looked at pistons, and they are all the same color, pretty dark. I will do a compression test tomorrow, but the engine seems to run good and quiet. Is this a sign of a bad head gasket? How bad could it be? I am pretty mechanically inclined, Is this a huge expensive p.i.t.a. job? I will order a service manual on Monday, does the dealer carry this? I would have to pull the engine and ship it to get it worked on, I live on an island with no Merc. dealer so I am trying to avoid this. If you have any ideas, please let me know. Thanks for the help-AA

 

[alaskanassassin]

Re: please help, head gasket?

Will a low compression reading show a bad cylinder, or will it read low due to a head gasket too? If I do get a low reading on a cylinder, would it be possible that the cylinder is still ok, but the gasket is bad? Thanks-AA

 

[j_martin]

Re: please help, head gasket?

Don't fret, it won't do any good.
Run the comression test. If it's good, likely you fried some electronics with the heat. If it's low on one or more, you'll have to pull the heads to figure it out. At that time you will be able to answer your own questions.

Being so remote, I'd think preventative maintenance would be high on your to-do list. Water pump should be an annual item. Controls checkout at least every other year, if not annual.

hope it helps
john

 

[alaskanassassin]

Re: please help, head gasket?

Thanks, John. You are right, maintenence is key around here, and I learned my lesson in a big way. I just bought the boat and motor last year. The outboard has about 25 hours on it now, and the previous owner had changed the impeller before the sale. I will be tearing into it as soon as my service manual gets here.