Mercruiser spark plug replacement question?

[lrdchaos]

Just picked up a new to me Mercruiser 350 mag. I’m looking to preform a tuneup and start fresh. I was looking at replacing spark plugs since the previous owner hasn’t changed them in a couple years. Look at the new iridium plugs, most current replacement part numbered plug, they are 18-20 a piece. I can find the original iridium plugs for 8 dollars a piece, these have the original(old) part numbers. My question is, is there that much difference between oe 41-993 plugs vs the new 33-8m2018369 plugs?

 

[Stinnett21]

Pretty sure that's just Mercury's number for the NGK 5599 plug at twice the price. I run the AC 41-993s in my 5.0 MPI. They run great.

 

[Rick Stephens]

Those plugs are easily good for 100,000 miles on the road, why change them?

 

[lrdchaos]

I was under the impression that plugs should be changed every couple of years if not annually.

 

[crazy charlie]

Plugs can be easily cleaned and regapped .After cleaning if they look completely intact then reuse them.Charlie

 

[alldodge]

Don't re-gap iridium plugs, this can break/crack the iridium coating

20 year champion plugs looked real nice when replaced, and new plugs didn't change any performance I could determine

 

[Bondo]

I was under the impression that plugs should be changed every couple of years if not annually.

Ayuh,..... Even the ole standby stock plugs, MR43T will last 5 or more years,.....

Boaters get pretty anal when it comes to parts that are reasonably easy to change,.....
Spark plugs, 'n coils come to mind,.....

 

[QBhoy]

The 5599 are what you’re after. Don’t need changed for years. My mpi didn’t perform well with the AC plugs you mention. They are platinum things I’m sure.

 

[Stinnett21]

Agree. When I changed from the MR43Ts to the iridium there was a noticeable performance increase. Of course Bondo wasn't attesting to performance only to longevity. So Manual 31 says every 300 hours. Maybe that was for the old style plugs. I'm there now so I've already bought 8 new iridiums to go in soon. Maybe I shot $90 for nothing.

 

[alldodge]

noticeable

 

[QBhoy]

I didn’t notice too much of a crazy performance increase, apart from a couple of extra rpm at the top. So a little... But most noticeable was the running a lot smoother and lasting longer for certain