It's amazing.....
 

How some people can be so lazy when purchasing spark plugs for a boat. Who in there right mind would by auto lite spark plugs for 454/420's? The port motor in my 1988 Formula 311 was running a little sluggish compared to the starboard motor so I decided to have it checked out. Pier 53 marina in Sandusky, OH told me it needed a tune up when they did the tranny work on it, so I was gonna do it in the spring but decided to have it checked out sooner so I wouldn't have to worry about it in the spring.

I'm having Kunkel's Marina near Mansfield OH do the work and the owner Jason calls me today and tells me that the motor has auto sparkplugs in it, I'm thinking WTF! turns out at one time there must have been a water leak somewhere near the #7 plug which caused it to rust and break apart so #7 wasn't firing at ALL. So that means the head has to come off and drill it out. Hopefully thats all that is wrong with it and he'll replace the AUTO plugs with Marine Plugs. Unbelievable.

There is nothing wrong with running automotive plugs in a marine engine as long as they are the correct plug. Marine spark plugs are pretty much the same except some brands of the marine plugs have an SS coating to prevent corrosion.

You stock plugs should be an AC MR43T. They are the same as an R43T except for the SS plating. Also the same an AC Rapid Fire #1 which has an SS coating.

There is a lot more selection for automotive plugs as well.

Good info. Thanks Griff

I run the racing autolite automotive plugs. But maybe your right im out of my mind. There is no issue with running the plugs. Ive never had a problem what so ever also I agree with griff on all points. Although there is a differance when you do your own work you get down in the bilge and always checking everything evertime the hatch opend just for piece of mind. I enjoy being a bilge rat ask any CT member on the board. Come down to making sure the the salt (if thats what you run in) is washed off completly and doing maintance when do and preventitive maintance.
-Mike

I replaced the plugs on a 7.4MPI once only to find they had been replaced by the previous owner with the wrong length plugs. I was amazed the motor ran as well as it did without the correct extended tip plugs. Heat range and length are the most important things to get right on a plug.

I am guessing that if you had pulled those plugs yourself you wouldn't have known any better. Sounds like a good ole mechanic trick telling you that they cannot believe what someone else did that they would never do; because "they know better."

Don't believe everything you are told unless you know for yourself. Otherwise, you will go on to a forum and tell a bunch of DIY'ers how you let your mech. blow smoke up your a$$.

I ran autolite's in by marine 572's. They were the only plug that they really "liked".

Sounds like you take of your stuff. So I'm sure there are exceptions for every boat. I quess if your going to keep a watchful eye on your equipment then you can get by without the SS coating. I just bought the boat and appears that these plugs were put in and forgotten about. Plus the mechanic seemed like using auto plugs was a no no.

+1 as long as heat and length are correct no issues especially inland.

I always ran AC rapid fire #1 in my 502's in Chicago

I found the same with my new to me boat. Plugs were short version, not extended length. Boat ran great, as far as I could tell. I put correct plugs in M43RT. ...hoping to get another MPH out of it now. ;-)

He may be able to get the plug out with an EZ-out instead of pulling the head off... A little heat on the plug and an EZ-out in place of the ceramic and he might be able to get it out.

I'd pay for an hour's worth of labor trying to do that before paying to R&R a head.