Mercruiser Spark Plugs

Stevcool

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Dec 29, 2011
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10
I have a 95 5.0 chevy 305 merc motor. I found a sale on autolite spark plugs and decided to change mine. At time I had them match to a 95 pickup truck with same motor. It came out with Autolite Ap25 Platinum Plugs.
However, when I changed the plugs I had the Al Deco mr43t plugs in the boat. I used crossrefrence on Autolite site and it came out as a basic 145 plug. I wanted the upgrade to platinum however I am concerned that this plug is not a perfect match. I have already installed them and engine runs great. However, When looking on autolite specs on website there is only one diffrence between the autolite 145 and ap25. The only diffrence in specs is Ap25 has heat range of E13 and the Autolite 145 has heat range of B13. They are both 13 but I can find nothing on the site that explains the diffrence of E13 to B13. Does anyone know this. I emailed Autolite with no response from them. I just dont want to mess something up.
 

Bondo

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Apr 17, 2002
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70,470
Re: Mercruiser Spark Plugs

However, when I changed the plugs I had the Al Deco mr43t plugs in the boat.
I wanted the upgrade to platinum

Ayuh,.... Why,..??

The AC Delco's are an alloy bodied plug, that generally don't rust into the heads, 'n has worked Perfectly for 'bout 40 Years now....
 

cr2k

Captain
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Mar 19, 2009
Messages
3,730
Re: Mercruiser Spark Plugs

Without electronic ignition fancy plugs are not a lot of help, You should change every year with summerization and tune up anyway.
 

120_i/o

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Jan 21, 2012
Messages
76
Re: Mercruiser Spark Plugs

I disagree with changing them every year...plugs last A LONG TIME. Plugs are the most common item to be replaced, and people waist money on em all the time.
 

ktbarrentine

Lieutenant
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Dec 12, 2011
Messages
1,296
Re: Mercruiser Spark Plugs

I disagree with changing them every year...plugs last A LONG TIME. Plugs are the most common item to be replaced, and people waist money on em all the time.
+1 on lasting a long time
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Re: Mercruiser Spark Plugs

On my previous engine (1994 4.3LX) I was replacing plugs (NGK BR6FS) at about 200-250 hours. On this current engine (2006 4.3MPI) even though it's got iriduim 'long-life' plugs, I'm getting about 200-250 hours... :rolleyes: go figure....
 

oldjeep

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May 17, 2010
Messages
6,455
Re: Mercruiser Spark Plugs

I disagree with changing them every year...plugs last A LONG TIME. Plugs are the most common item to be replaced, and people waist money on em all the time.

x3 - I pull and check mine every year, only actually replaced them once since 2005 - this year will be #2
 

blhdiscgolf

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Joined
Apr 16, 2005
Messages
13
Re: Mercruiser Spark Plugs

Sorry, I don't mean to hijack this thread, but I can see no where that I can under a category post my own thread. Hope someone reads this and can advise.

Recently when starting my 2005 Tahoe Q4 4.3L Mercruiser, the boat when put in wakespeed exiting the marina runs a bit rough, almost sounds like a slight miss. However once out on the open water and ran for 3-5 minutes and returning to wakespeed it just purrs along as it normally does. I pulled the top cover off the Carb and everything looked clean as a whistle, so after much ado I managed to remove a cardboard side engine panel and got to my spark plugs. However instead of finding a AC MR43LTS, I found someone when tuning my boat up a cpl years back put in AC 41 932 plugs in their place. The Factory info on the Carb cover directly indicates to use the MR43LTS gapped .45 at all times. The plug I pulled was brown and the white core facing the spark had a brown streak running from top to bottom.
I suspect I should probably remove all 6 plugs, which is pure joy, you almost need to be a contorsionist to get to them and apply any strength to gently break them loose.
Anyone know why someone would put the AC 41 932 plugs as a replacement, I have not found anything online that indicates this plug co-exists as a cross ref to the 43MRLTS at all.

Brian
 

Don S

Honorary Moderator Emeritus
Joined
Aug 31, 2004
Messages
62,321
Re: Mercruiser Spark Plugs

Sorry, I don't mean to hijack this thread, but I can see no where that I can under a category post my own thread. Hope someone reads this and can advise.

Brian

Seems you haven't posted since 2005 and your permissions have changed. I will get the IT guys to fix it for you, then you will be able to start your own thread.
 
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