Spark Plug Problem

[JWC]

I have a 2004 22V that I bought used with about 40 hours on it. Over the weekend I had a spark plug blow out. The threaded piece at the base of the plug actually stayed in the head but the whole center of the plug (porclean down through the electrode) seperated and blew out of the cylinder and actually started a small fire. Has anyone heard of this or have any idea what might have caused it? I replaced the plug and it seemed to work fine but I am concerned about what might have caused it.

[raythompson]

It was just a bad plug. I would doubt there was any damage as the cylinder was now just a free breather.

[TeamAllen]

Some of the plugs are very close to the exhaust manifold. Maybe when it was installed the angle of the socket cracked the porcelin section of the plug and it just hung in there for awhile till it blew. Glad everybody is ok and your new plug is working out.

[Andrew]

I do not think you hurt anything, however I would keep an eye on that plug and if you start burning oil. Check the plug in approximately 20 hrs and see how its burning. That will tell everything. If you still feel unsure then make an appointment with the dealer and have them check things out after you put the 20 hrs on the boat.

Andrew

[jsz]

while were on plugs, what plugs are you guys using and how often do you change them. My boat runs fine but I thought about changing them anyway until the lady @ my local merc supplier told me they were about $16 each. Does that sound high to anyone else?

[TeamAllen]

I use NGK. I change them every season. BPR6EFS, about $2-$3 a piece. Maybe you have a different plug. There are some iridium plugs out there that are the expense you mentioned. I have them in my Toyota Sequoia.

[jsz]

thanks teamallen. i guess i should have mentioned i have a 02 merc 350 MPI. i heard it takes platinum plugs but $16 seems outreegis.

[jsz]

Did that NGK come with the correct gap?
Is it a platinum plug?
Does merc call for platinum plugs? I'm only asking because thats what the lady said she had for my boat.

[jsz]

I just saw another thread where some guys were using bosch plugs. Does anyone else have any input for a "bang for the buck" plug?

[TeamAllen]

I always check the gap on the plugs anyway, so I'm not sure if they were gapped right out of the box. If they need any adjustment, it is minimal.

The only reason to use a special plug, like platinum or iridium is for longevity. If you change your plugs frequently, you are wasting your money on a longer lasting, more expensive plug.

[jsz]

Good tip, thanks. This is the 3rd season I've had the boat and I haven't changed the pugs yet. I've never had any problems and the motor seems to run great. I don't want to wait too long but I don't want to throw out good plugs either. When I gave the shop the # on the plug they said it was platinum. Maybe thats why it's lasting so long, like you said.

[drgibson]

I use AC/Delco Marine plugs. Oddly enough, O'Riellys Auto Parts stocks them for about $3 apiece. I change them every two or three years and it makes a lot of difference.

[teachercop]

I also use the AC/Delco Marine plugs,,,got them at the Carquest for approximately $2 each. MerCruiser 315 mpi. Also changed Dist cap and rotor at the same time,,,part of my 'summerization' program. Has anyone changed the plug wires? I have not (400 hours) as I felt it was unnecessary ,,I did not think the wires had lost their effectiveness....