Upnorth here with my family and just ran around the lake in my parents 17 ft runabout. The engine made a funny sound and and acted like it was running on 3 cyclinders. We pulled the plugs and one had the tip melted and the ceramic was cracked. What is the problem? And if it is a plug issue is damage already done to the cyclinder?

More Then Likly Sounds Like A Lean Run Condition, You Need To Do A Compression Test Might Have A Hole In The Cylinder

Can you give a little more detail! Is there anything we can look or check ourselves. The motor is a 3 liter mercrusier.
We our up here on a weeks vacation with all the kids and of course they are chomping at the bit to go sking tubing etc.

Were the plugs loose when you took them out? That will cause that.

If its running lean, change the fuel filters and plugs.

Is the motor ticking, knocking, or popping? Throw a new set of plugs in it and change the gas filters. If it pops thru the intake or exhaust, you probably have internal damage such as bent valve, head gasket, etc.

once you put the new plugs in, fire it up and pull the oil filler cap. If smoke is coming out a lot, you might have a cracked piston or a hole in it. Keep it simple for now, get the plugs and gas filter.

My brother-in-law changed the plugs just before we came up north and yes he thinks that one was loose!

If a spark plug is loose, it will quickly overheat and burn the tip. It has to be torqued (tight) in the cylinder head to make compression AND to transfer (its) heat into the cylinder head.

If the engine wasn't run very long in this condition, you may be lucky with new plugs. Keep your fingers crossed.

The fuel filter was changed just before we came up north, should we still change it again.

Nah, no need to.....if the plug was loose. If none of the other plugs were burned and/or excessively white on the tip, install new plugs (torque correctly) and take it for an easy run. Check for normal power, RPM, etc. If no popping, knocking, ticking.......enjoy the rest of your vacation.

Thanks Guys! We are going to take it in for a compression test on Monday and go from there.